Soft Tissue Pathology

Rakesh C A

Introduction

• The imaging evaluation of the soft tissues has undergone a rapid evolution with the application of computed tomography (CT), magnetic resonance imaging (MRI), and recently high resolution ultrasound (US).

• Consideration must be given to the financial costs and invasiveness of each technique balanced against the diagnostic reward.

• No examination should be reported in isolation without knowledge of relevant clinical details and results of previous investigations.

What is Soft Tissue???

• Soft tissue – derived primarily from mesenchyme and – consists of • skeletal muscle, • fat, • fibrous tissue, • the vascular structures• the peripheral nervous system.

IMAGING TECHNIQUES

Radiography

• The relative lack of soft tissue contrast resolution is a well-recognized limitation of radiography.

Only those structures exhibiting a radiodensity sufficiently different to that of water can be

distinguished from other soft tissues.

Less than muscle - fat and gas Increased radiodensity - haemosiderin deposition,

mineralization, be it calcification or ossification, and certain foreign bodies

• A low kilovoltage technique will accentuate the density differences between fat and muscle.

• Density differences can also be maximized with digital radiography where the broad exposure range means that it is difficult to make an inadequate exposure. A free choice of data processing allows control of the grey scales, contrast, etc., which can be optimized to highlight soft tissue disease.

Radiograph - Caution!!!

• When evaluating a radiograph it is important to remember that numerous extraneous factors may mimic soft tissue abnormalities. These include skin folds, clothing, hair artefacts and companion shadows.

• Also, iatrogenic conditions may pose diagnostic problems to the unwary such as the sites of old bismuth injections in the buttocks and tantalum gauze previously used in hernia repairs.

Ultrasound• Diagnostic ultrasound has been applied to the musculoskeletal system since B-mode techniques

became available. There have been rapid developments in ultrasound technology over recent years and these, along with the have resulted in a vast expansion in the evaluation of the soft tissues.

• Advantages of ultrasound include – widespread availability of ultrasound and – relatively low cost,– solid from cystic – abnormal tissue from normal variants such as accessory muscles– its real-time ability to assess structures dynamically, – its capability, using Doppler technology, to assess vascular flow and – to guide interventional procedures such as joint aspirations and soft tissue biopsies.

Solid vs cystic

• The advent of high frequency (>10 MHz) transducers with their improved spatial resolution, along with other developments such as multifrequency transducers, compound imaging and beam steering, has meant that further applications for musculoskeletal ultrasound continue to be introduced.

• Tendons, ligaments, nerves and muscle are now readily shown with ultrasound.

Ultrasound - Trade off!!!• The physics of ultrasound means there will always be a trade-off

between image resolution and depth of penetration. • Nevertheless the majority of musculoskeletal soft tissue structures lie

superficially and are readily amenable to high resolution ultrasound assessment.

• Disadvantages:– some deeper structures, such as the deep musculature about the adult hip,

remain difficult to assess– larger patients. – unable to see behind or into bone. – relatively limited field of view (extended field of view imaging has gone some

way to resolve this issue)– marked operator dependency – poor demonstration of findings on hard copy images;

Computed tomography • The introduction of computed

tomography (CT) proved a revolution in the detection of soft tissue masses and the preoperative staging of soft tissue tumours.

• CT, by virtue of its ability to assign a numerical value (Hounsfield number) to X-ray attenuation, produces good qualitative and quantitative assessment of soft tissues, offering an opportunity to distinguish the nature of a mass whether it is muscle, fat, fluid or tumour, and not solely on morphology.

• The high spatial resolution of CT, of the order of 1 mm, allows for masses as small as 1 cm to be detected, depending on differential attenuation between the lesion and the surrounding soft tissues.

• The contrast sensitivity and cross-sectional ability of CT will reveal soft tissue masses and calcifications that are not visible on conventional radiography.

• Lesion conspicuity can be increased with intravenous (IV) iodinated contrast medium.

• Narrow window settings are required for small density differences.

• The full extent of a lesion can be displayed by performing multiplanar reconstructions.

Magnetic resonance imaging

• advantage – not using ionizing radiation.– superior soft tissue contrast resolution and – multiplanar capability

• Soft tissue lesions can be categorized by MRI according to– site, – morphological changes and – signal characteristics – helped by multitude of

sequences.

• Contrast enhancement following the IV injection of a gadolinium chelate will result in a decrease in the T1 relaxation time and show up soft tissue lesions due to their different vascularization and perfusion. Enhancement can be most clearly identified on fat-suppressed T1-weighted images but enhancement is rarely necessary in the detection of soft tissue abnormalities where fat-suppressed T2-weighted or STIR sequences will suffice without the additional expense of the contrast medium.

• Similarly, many soft tissue abnormalities can be adequately categorized on MRI without contrast medium, e.g. ganglion, lipoma, haemangioma, etc. In equivocal cases, contrast agents can be of value in helping to distinguish cystic from solid lesions and thereby identifying the most appropriate portion of a lesion to biopsy.

• MRI is the best technique for staging soft tissue tumours and for follow-up. With the increasing use of adjuvant chemotherapy for soft tissue sarcomas, dynamic contrast-enhanced techniques will be increasingly used to assess angiogenesis and response.

Radionuclide imaging • Numerous soft tissue lesions concentrate bone-seeking radiopharmaceuticals. Any soft tissue

abnormality with the propensity to develop mineralization can show ectopic activity on skeletal scintigraphy. These include congenital abnormalities such as fibrodysplasia ossificans progressiva , collagen vascular disorders such as dermatomyositis, trauma as in myositis ossificans and neoplasia as in extraskeletal osteosarcoma and synovial sarcoma.

• Skeletal scintigraphy may be helpful in assessing the maturity of ectopic ossification as can be seen with spinal cord injuries. In this situation surgical resection is best deferred until the ossification becomes stable to minimize the risk of recurrence.

• Scintigraphy is not routinely indicated in the surgical staging of soft tissue sarcomas. Local osseous extension is uncommon and is best demonstrated by MRI. Bone metastases from soft tissue sarcomas are rare in the absence of disseminated disease elsewhere, notably the lungs, but can be seen in alveolar soft part sarcoma and rhabdomyosarcoma.

• Positron emission tomography (PET) with [F-18] fluorodeoxyglucose has not yet been widely studied for soft tissue lesions; it can be used to assess soft tissue tumour metabolism in order to grade tumours and to assess relapse. It may also be helpful in assessing malignant transformation of peripheral nerve sheath tumours in neurofibromatosis

RADIOGRAPHIC OBSERVATIONS

Calcification And Ossification

• The deposition of amorphous calcium salts within the soft tissues is variously called mineralization or calcification.

• Two forms of calcium salts may be found in the soft tissues: calcium pyrophosphate dihydrate and calcium hydroxyapatite.

• If bony trabeculae are discernible within the mineralized focus the term ‘ossification’ is used, sometimes prefixed with the terms ectopic or heterotopic.

• There is a wide differential diagnosis, which can be divided into – generalized calcification, – localized calcification and – ossification

Generalized Conditions

Generalized Conditions

Metabolic disorders • Prolonged elevation of the serum calcium or, more importantly, the

serum phosphate. • In primary hyperparathyroidism

– typically seen in arteries, cartilage (chondrocalcinosis) and the periarticular tissues.

– uncommon today as primary hyperparathyroidism is usually detected by identification of serum biochemical abnormalities before the more florid radiographic abnormalities have the opportunity to develop.

• In secondary hyperparathyroidism, typically associated with renal failure, – arterial and soft tissue calcification are frequent findings. – Periarticular calcification is a prominent feature, particularly in those on long-

term renal dialysis. – Conversely, chondrocalcinosis is an infrequent finding in secondary

hyperparathyroidism

Chronic renal failure (two different cases). (A) PA hand radiograph showing the florid features of secondary

hyperparathyroidism including terminal phalangeal resorption, soft tissue calcification, subperiosteal resorption, vascular calcification and osteopenia.

(B) Tumoral calcinosis with heavy periarticular calcification

• In hypoparathyroidism there is a deficiency in parathormone (PTH), usually secondary to excision or surgical trauma but rarely idiopathic. Subcutaneous calcification, basal ganglia calcification, osteosclerosis and premature closure of epiphyses are typical of the primary disease. Occasionally, band-like paraspinal calcification may be seen mimicking diffuse idiopathic skeletal hyperostosis.

• Pseudohypoparathyroidism, a rare inherited X-linked dominant disease in which there is end-organ resistance to PTH, exhibits similar features to hypoparathyroidism. Features that distinguish it from hypoparathyroidism are growth deformities, with broad bones and cone epiphyses, brachydactyly with short metacarpals and metatarsals, especially the first, fourth and fifth, and small exostoses projected at right angles from the bone.

• In pseudopseudohypoparathyroidism, in which the serum calcium and phosphate levels are normal, the radiographic abnormalities are identical to those of pseudohypoparathyroidism.

• Hypervitaminosis D usually occurs due to the administration of excessive levels of the vitamin in the treatment of rickets and osteomalacia but can also be found in granulomatous diseases, Paget's disease and rheumatological conditions such as rheumatoid arthritis and gout. Smooth, lobulated amorphous masses of calcium, usually calcium hydroxyapatite, occur in the periarticular regions, bursae, tendons sheaths, and both within the capsule and cavity of joints. The bony manifestations of vitamin D intoxication depend on the age of the patient, with dense metaphyseal bands and cortical thickening with or without generalized osteosclerosis seen in infants and children. Adults merely show varying degrees of osteoporosis.

• A generalized increase in bone density is a feature of idiopathic infantile hypercalcaemia where there are associated clinical manifestations of hypotonia and mental and physical retardation. The condition is thought to be due to inappropriate sensitivity to vitamin D.

• Milk-alkali syndrome is reported in patients with chronic peptic ulcer disease and renal impairment in whom the excessive ingestion of alkali, usually calcium carbonate, and milk leads to diffuse calcifications in the soft tissues, kidneys and eyes. Reversibility depends on the chronicity of the disorder. The soft tissue calcifications are typically periarticular, amorphous and vary in size from small nodules to large masses. Similar deposits may be seen in renal osteodystrophy, collagen vascular disorders, hypervitaminosis D and idiopathic tumoral calcinosis.

• Deposits of monosodium urate in gout, so-called ‘tophi’, are not radio-opaque. However, calcification within the tophi can occur as a secondary phenomenon. The incidence of chronic tophaceous gout has decreased considerably with the introduction of effective anti-uricaemic drugs.

Generalized Conditions

Arterial calcification• Some degree of arterial disease is an almost

inevitable part of the ageing process in the developed world so that atheromatous calcification is considered a normal variant on most radiographs in middle-aged and elderly patients. The spectrum of calcification ranges from irregular plaques to extensive tramline calcification predominantly affecting the aorta and pelvic and lower limb arteries.

• Finer ‘pipe-stem’ calcification is seen in medial degeneration (Mönckeberg's arteriosclerosis) which also shows a similar propensity for the lower limbs, as does the calcification associated with diabetes mellitus.

• A finer more generalized pattern of arterial calcification is seen in renal failure and hyperparathyroidism.

• Rounded, curvilinear or crescentic calcification is a typical feature of aneurysms on radiographs irrespective of site.

Venous calcification • Venous mural calcification is rare• Small circular calcified densities,

phleboliths, are common, especially in the pelvic veins. – also seen in chronic varicosities and

haemangiomas, most frequently cavernous ( Fig.A ).

• Phleboliths may be the only radiographic soft tissue abnormality indicative of haemangiomas in patients with Maffucci's syndrome, which is the combination of multiple enchondromas (Ollier's disease) and haemangiomas ( Fig.B ).

• Subcutaneous calcification and organized periosteal new bone formation may occur in chronic oedema associated with venous incompetence.

Generalized Conditions

Bacterial• Diffuse calcification is extremely

rare in bacterial infection. Dystrophic calcification may occur in resolving abscesses, particularly in tuberculosis of the spine.

• Extensive calcified lymphadenitis is highly suggestive of an old tuberculous infection and, in endemic areas, the fungal infections histoplasmosis and coccidioidomycosis.

• Leprosy is a rare cause of nerve calcification.

Parasitic

Cysticercosis Guinea worm

Generalized Conditions

Congenital • Fibrodysplasia ossificans

progressiva – Previously known by the synonym

myositis ossificans progressiva – inherited autosomal disorder.– progressive swelling and

ossification of the fascia, aponeuroses, ligaments, tendons and connective tissue of skeletal muscle,

– entirely unrelated to myositis ossificans.

– The initial manifestation is swelling of the muscular fascial planes, usually affecting the neck and shoulder girdle first, before the onset of multifocal calcification progressing to ossification.

Fibrodysplasia ossificans progressiva. (A) Posterior 3-h skeletal scintigram of the trunk showing linear foci of increased activity corresponding to the soft tissue ossification. (B) Chest radiograph showing bilateral chest wall ossification.

Congenital • Fibrodysplasia ossificans

progressiva – Early changes can be detected by

CT, MRI and skeletal scintigraphy– The progressive ossification

produces large masses that can bridge between bones, which in the thorax can result in respiratory compromise.

– The disorder can be suspected before the development of soft tissue swellings by identification of associated skeletal abnormalities.• short first metacarpals and

metatarsals • small cervical vertebral bodies

with relative prominence of the pedicles.

Fibrodysplasia ossificans progressiva. (A) Posterior 3-h skeletal scintigram of the trunk showing linear foci of increased activity corresponding to the soft tissue ossification. (B) Chest radiograph showing bilateral chest wall ossification.

Acquired

Crystal deposition diseases Crystal deposition in a joint will stimulate a synovitis due to one of the following crystalline arthropathies:

1. gout

2. calcium pyrophosphate dihydrate deposition disease (CPPD)

3. calcium hydroxyapatite deposition disease (HADD)

4. mixed crystal deposition disease.

CPPD

• CPPD is the general term for the deposition of calcium pyrophosphate dihydrate crystals in and around joints, and in the annulus of the intervertebral disc.

The latter is a useful distinguishing feature from ochronosis which involves the nucleus pulposus.

• There are three manifestations of CPPD, – acute intermittent synovitis (pseudogout), – chronic pyrophosphate arthropathy and – chondrocalcinosis

• Pyrophosphate arthropathy has many similar radiographic appearances to osteoarthritis.

• It is for this reason that many cases will pass through orthopaedic clinics simply labelled as osteoarthritis.

• Features suggestive of pyrophosphate arthropathy include – unusual distribution (e.g. patellofemoral, radiocarpal and

elbow joints), – prominent subchondral cyst formation and – relative paucity of osteophytes.

• Chondrocalcinosis affects both fibrocartilage (menisci, triangular fibrocartilage, symphysis pubis and annulus fibrosus) and hyaline cartilage of the knee, wrist, elbow and hip.

• CPPD is associated with many conditions, such as hyperparathyroidism, haemochromatosis, gout, Wilson's disease and diabetes mellitus. Chondrocalcinosis of the menisci.

Ossification adjacent to the medial femoral condyle indicates old medial collateral ligament injury (Pellegrini–Stieda lesion).

Calcium hydroxyapatite deposition disease (HADD)

• HADD typically has a monoarticular presentation in the middle-aged and elderly.

• It is characterized by homogeneous cloud-like periarticular calcification, most commonly affecting the shoulder in and around the supraspinatus tendon.

• Aetiology is thought to be related to repetitive minor trauma with a cycle of necrosis and inflammation leading to dystrophic calcification.

• Over time, dependent on the clinical course, the calcifications may increase in size, remain unchanged or regress.

Calcium hydroxyapatite deposition disease (HADD). Heavy calcification in the distal supraspinatus tendon.

Dermatomyositis • This is a condition of unknown aetiology that

produces inflammation and muscle degeneration.

• It is frequently associated with nonspecific subcutaneous calcification with less common, albeit characteristic, sheet-like calcification along fascial and muscle planes, particularly involving the proximal large muscles.

• The major differential diagnoses– idiopathic calcinosis universalis – hyperparathyroidism.

• The childhood form may be associated with hypogammaglobulinaemia or leukaemia.

• In older patients it may be associated with malignancy; the most common associations are with carcinoma of the bronchus, breast, stomach and ovary.

Progressive systemic sclerosis (scleroderma)

• This condition, with unknown aetiology, causes small vessel disease and fibrosis in several organs.

• Scleroderma is the cutaneous manifestation of the disease.

• It often presents with Raynaud's phenomenon and skin changes.

• Typical features in the hands are terminal phalangeal resorption (acro-osteolysis) due to pressure atrophy, discrete dense plaques of calcification (calcinosis circumscripta) and occasional intra-articular calcification.

• Erosive changes can occur which may be due to concurrent rheumatoid arthritis or some form of overlapping condition.

• The related CREST syndrome is due to the combination of calcinosis, Raynaud's phenomenon, oesophageal dysmotility, scleroderma and telangiectasia.

• The only radiographic difference from that described above is that the calcification may also involve the tendon sheaths.

Scleroderma. Widespread digital calcification (calcinosis circumscripta).

Generalized Conditions

Tumoral calcinosis• Autosomal dominant condition, • biochemical defect of phosphorus metabolism. • normal serum calcium level • renal, metabolic and collagen vascular

disorders have been excluded. • It leads to large multilocular juxta-articular

cystic lesions filled with calcific fluid (calcium hydroxyapatite) with or without fluid–fluid levels.

• By virtue of their site and size, these masses can lead to restricted joint motion, bone erosion and superficial ulceration and secondary infection.

• Treatment relies on phosphate depletion. • Surgery is frequently associated with

recurrence of the mass.

Tumoral calcinosis with heavy periarticular calcification.

Localized Conditions

CALCIFICATION—LOCALIZED

• The first radiographic sign of soft tissue mineralization will be faint calcification.

• In time this may become more extensive and therefore more conspicuous.

• Alternatively, in certain conditions the mineralization can develop into woven bone. Therefore, localized calcification may be the precursor of conditions typically associated with ossification.

Trauma

• Any condition that results in focal soft tissue necrosis may predispose to calcification. – These include injection sites, radiation damage to the soft tissues

and thermal injuries, both burns and frost-bite. • Blunt trauma may cause fat necrosis within the subcutaneous

tissues with areas of dystrophic calcification. • Calcification of atrophic muscles may be seen 1–2 months

after severe crush injury (calcific myonecrosis). • Any haematoma, particularly if in a subperiosteal location,

may calcify. – This includes the subperiosteal (pericranial) haematoma seen in the

skull of babies, usually as a result of birth trauma.

Tumours • Widespread soft tissue calcification is a rare

manifestation of disseminated malignancies (e.g. metastases, leukaemia and myeloma) where there is hypercalcaemia associated with extensive bone destruction.

• Localized intratumoral calcification may occur within any soft tissue tumour due to haemorrhage and/or necrosis.

• Benign soft tissue tumours with the propensity to mineralize include soft tissue chondromas (punctate or ‘ring-and-arc’ calcification), lipomas, particularly if in a parosteal location (ossification), haemangiomas (phleboliths) and soft tissue aneurysmal bone cyst.

• The typical malignant soft tissue tumours that calcify are extraskeletal osteosarcoma, extraskeletal chondrosarcoma and synovial sarcoma . In the latter entity calcification occurs in approximately 30% of patients with a central rather than a peripheral distribution.

• A rare benign tumour that can mimic myositis ossificans with peripheral calcification is the ossifying fibromyxoid tumour of soft parts.

Synovial sarcoma. Axial CT demonstrating a soft tissue mass lateral and posterior to the femur containing calcifications.

OSSIFICATION • Many calcifying lesions may proceed to

ossification with the production of woven bone. • The deposits of calcium salts tend to be more

densely sclerotic than comparable amounts of bone. If there is doubt, CT can readily distinguish the amorphous quality of calcium salts from the trabecular pattern of ossification.

• Heterotopic ossification is a common complication of many conditions and is thought to be due to inappropriate differentiation of fibroblasts into osteoblasts in response to a local inflammatory process.

• Developmental causes include fibrodysplasia ossificans progressiva, melorheostosis and progressive osseous heteroplasia.

• The majority of other causes of heterotopic ossification are traumatic in origin.

• Soft tissue ossification as a result of surgery is well recognized, particularly after total hip arthroplasty. – In most cases the ossification is of

little clinical significance.

• Post-traumatic or post-surgical ossification is common in tendons and ligaments.– Examples include the Achilles tendon

and the medial collateral ligament of the knee (Pellegrini–Stieda lesion).

• Ossification may occur in patients with severe thermal and electrical burns.

• Acute detachment or repeated trauma to a tendino-osseous junction can lead to soft tissue ossification with underlying cortical irregularity.

• In the skeletally immature, an avulsed ossification centre may continue to grow, presenting at a later stage with a large ossified mass in the soft tissues.

• These types of avulsion injury classically affect the pelvis, particularly the origin of the hamstrings.

Ischial avulsion. (A) Radiograph at presentation shows

the avulsed ischial apophysis lying in the soft tissues.

(B) Three years later the apophysis has continued to grow to form a large ossified mass

• Trauma can also be an indirect cause of soft tissue ossification when associated with injuries to the central nervous system, be it prolonged unconsciousness or spinal trauma.

• In this situation it is known as neurogenic heterotopic ossification.

• It typically exhibits a periarticular distribution with the hips most commonly affected.

• The shoulders and elbows are usually only involved with head or higher spinal injuries.

• Surgical excision is frequently associated with recurrence.

• Heterotopic bone formation in muscles, tendons and fascia following trauma is known as myositis ossificans.

• A very similar condition (radiographically and pathologically) occurring in the absence of trauma is the pseudomalignant osseous tumour of soft tissues; this is also known as pseudomalignant myositis ossificans.

Myositis ossificans. (A) Axial CT at presentation showing early

peripheral mineralization. (B) Six weeks later there has been

maturation with well-organized peripheral ossification

• Initially there is interstitial haemorrhage with subsequent mineralization.

• The mineralization is seen first in the periphery; there is a gradual reduction in size of the mass .

• Both are helpful distinguishing features from a mineralizing soft tissue sarcoma.

• The lesions will appear hypervascular on angiography and show increased activity on bone scintigraphy.

• Where possible, early biopsy should be avoided as the immature lesion can pathologically resemble a soft tissue osteosarcoma.

• The MRI features of the early lesion can also be confusing showing florid perilesional oedema involving the whole affected muscle compartment on T2-weighted or STIR images

Myositis ossificans. (A) Axial CT at presentation showing early

peripheral mineralization. (B) Six weeks later there has been

maturation with well-organized peripheral ossification

GAS IN SOFT TISSUES

• Gas/air may be introduced into the soft tissues from within and without the body.

• It may also be formed directly within the soft tissues. Gas in the soft tissue can be recognized radiographically by increased radiolucency outlining the soft tissue planes.

• Care should be taken not to confuse ectopic viscera with soft tissue gas. A prime example would be bowel gas within an inguinal hernia which can overlie the soft tissues of the groin or scrotum.

Gas introduced from within • Air may enter the soft tissues

whenever there is a breach in the integrity of the lining of either the respiratory or gastrointestinal tract.

• In the chest and retroperitoneum this is known as surgical emphysema.

• Common causes in the chest include – blunt trauma with a fractured rib

puncturing the lung, – penetrating lung trauma and – following chest surgery. – complication of interventional

procedures such as the insertion of central lines and biopsy and drainage procedures.

Gas introduced from without • Air may be introduced into the

soft tissues as a result of penetrating injuries or compound fractures.

• This can be distinguished from infection in that it is present on the initial radiograph, whereas the gas associated with infection usually takes several days to develop.

• Frequently, air can be identified within joints and soft tissues following therapeutic injections and surgical procedures.

Gas arising within the body • Gas formed within the soft tissues is a

manifestation of infection. • The classic example is gas gangrene

which is a bacterial infection caused by several clostridial species. The infection usually follows open, contaminated wounds with concomitant vascular compromise.

• Another form of clostridial infection is anaerobic cellulitis where the gas is confined to the subcutaneous and superficial fascial layers.

• Other anaerobic infections producing gas include coliforms, anaerobic Streptococcus, Bacteroides and Aerobacter aerogenes. – less severe – more localized collections of gas.

Clostridial osteomyelitis. The axial CT shows the relatively hypodense abscess collection surrounding the abnormal femur containing multiple loculi of gas.

Soft Tissue Infection

SOFT TISSUE INFECTION

• Infections in the soft tissues are common and may require percutaneous or surgical intervention.

• Gas may be seen in the soft tissues in association with infection

• The appearance of soft tissue calcification seen with parasitic infections, healing abscesses and tuberculosis.

• With the exception of soft tissue swelling and blurring of normal fat planes, most soft tissue infections do not give rise to radiographic changes and cross-sectional imaging techniques are required.

Abscess• Abscesses may develop in the soft tissues

either from extrinsic sources, for instance following a puncture wound, or from an intrinsic source either via haematogenous spread or direct spread from a nearby source such as a bowel fistula or infected joint.

• US - appear as predominantly cystic structures, often of a complex multiloculated nature with posterior acoustic enhancement. The cyst contents can vary considerably in echogenicity depending on the nature of the collection and on the amount of soft tissue debris present, and may be shown to swirl around with gentle probe pressure.

• Although the collection itself will not show any Doppler signal, the tissues surrounding the collection may appear markedly hypervascular

Abscess collection. Transverse US with power Doppler. A largely anechoic collection lying in the thigh of this diabetic patient was found to contain pus. Note the marked vascularity of the soft tissues surrounding the collection shown

• In cases where the infection has resulted from the introduction of a foreign body, this may be still present.

• Although radio-opaque matter may be seen on conventional radiographs, ultrasound is excellent for looking for non-radio-opaque foreign bodies Wooden foreign body.

Transverse US. A piece of bamboo cane seen here in transverse section (arrow) is located in an abscess collection in the subcutaneous tissues of the upper arm. Note the acoustic shadowing behind the foreign body.

• MRI and CT will also both show abscess collections and may be required for deep-seated abscesses such as those in the psoas muscle or deep gluteal region.

• US or CT is ideally suited for guiding aspiration and drainage of soft tissue abscess collections.

• CT will usually show abscesses as– a nonenhancing area of

lower attenuation than the surrounding tissues, although the presence of haemorrhage or very proteinaceous fluid may result in increased attenuation.

– The surrounding tissues may enhance following intravenous contrast medium.

• On MRI the collection will be of – low to intermediate signal

on T1 weighting and – high signal on T2

weighting and – peripheral enhancement

with gadolinium. – Oedematous change in

the surrounding tissues often with a rather feathery appearance.

Pyomyositis

• In the western world pyomyositis is most frequently seen in immunocompromised individuals.

• MRI best shows – generalized change seen throughout the affected muscle– heterogeneous increased signal on T2-weighted imaging,

• Ultrasound will also show – generalized alteration in echogenicity.

• As the disease progresses, small pockets of fluid form within the muscle with similar imaging characteristics to abscesses.

• MRI is the most sensitive investigation in pyomyositis.

Cellulitis • Cellulitis represents a superficial infection involving the subcutaneous tissues. • Clinically the tissues appear erythematous and swollen. • Imaging reveals thickening of the skin and subcutaneous tissues. Fluid is seen

tracking between the lobules of subcutaneous fat. • On Ultrasound

– low reflective septa, • On T2-weighted MRI

– these thickened septa yield increased signal. – Increased signal is also seen in the skin itself and underlying fascia.

• Since these changes are nonspecific and will be seen with noninfective causes of soft tissue oedema, clinical correlation is essential.

• Imaging remains useful to demonstrate any associated abscess formation and may be required to exclude involvement of other local structures such as bone or joint.

NEUROMUSCULAR DISORDERS

NEUROMUSCULAR DISORDERS• A wide-ranging and diverse group of conditions can be considered under the

broad heading of neuromuscular disorders. These include the congenital and acquired myopathies and neuropathies, all of which bring about muscle changes as their end point.

• Conditions include – those affecting the nerve supply to muscles, such as the congenital and acquired

spinal muscle atrophies and peripheral neuropathies, and – those affecting the muscles themselves such as the congenital, inflammatory and

metabolic dystrophies and myopathies. • The key changes seen in muscle pathology (seen on imaging) are

– hypertrophy and atrophy, – oedema-like change– fat infiltration and – calcification.

The term ‘oedema-like’ change is preferred to oedematous, as muscles showing this change on MRI are not actually oedematous when examined histologically.

Conventional radiographs

• Limited role to play in the diagnosis of these conditions. – Fat atrophy may be apparent on plain radiography – Calcification within skeletal muscle can be seen

both following trauma (as in myositis ossificans) and in inflammatory conditions such as dermatomyositis.

Ultrasound

• Hypertrophy and atrophy may be detected – difficult to appreciate when generalized.

• Fat infiltration is easier to recognize on US – normal striated architecture of the muscle is lost and the affected

muscles show an increase in reflectivity. • Advantages:

– when nerve compression is suspected as many of the peripheral nerves can be easily followed and causes of nerve entrapment may be identified.

– role in guiding muscle biopsies. • The main disadvantage of US

– small field of view, which makes it a difficult tool for examining generalized muscle conditions.

CT

• Atrophy, hypertrophy and fat infiltration are easier to identify on CT

• larger areas of muscle can be screened effectively.

MRI

• Normal muscle shows intermediate signal on both T1- and T2-weighted imaging.

• Indeed, when MRI changes are reported as showing high or low signal, this is usually assessed relative to skeletal muscle.

• Fat appears bright on T1-weighted imaging and its signal can be suppressed using standard techniques such as inversion recovery and spectral fat suppression.

• Consequently fat infiltration of muscle is easy to recognize on MRI.

• Oedema-like change in muscle will appear as increased signal on T2-weighted imaging, and this is most clearly shown on fat-suppressed T2 and STIR imaging.

MRI - technique

• T1 and fat-suppressed T2 (or STIR) sequences are fundamental to the diagnosis of neuromuscular disorders.

• coronal and sagittal imaging– useful in assessing the longitudinal extent of muscle

involvement, • axial imaging

– demonstration of the muscle compartments for identifying patterns of muscle involvement and the individual muscles or muscle groups involved.

– making comparisons with contralateral side in asymmetrical disease.

MRI in neuromuscular pathology

• The signal changes seen on MRI in neuromuscular pathology are nonspecific

• Generally not helpful in distinguishing between different types of disease.

• The pattern of signal intensity does give some useful information about the chronicity of a muscle disorder. – Fat infiltration represents a long-standing irreversible

process, – while oedema-like signal change represents acute or

subacute and potentially reversible muscle damage.

Muscle denervation

• MRI is not very sensitive to early changes in muscle following denervation.

• The earliest reliable changes are seen after around 1 month – the affected muscle or muscles yielding increased

signal on T2-weighted and STIR imaging. • About a year after denervation – fatty infiltration becomes apparent

Soft Tissue Injury

SOFT TISSUE INJURY

• The advent of MRI and high resolution US has revolutionized our ability to image soft tissue injury.

• Soft tissue injuries can be grouped into acute injuries or more chronic injuries which generally occur as a result of sustained or repetitive trauma.

• A brief overview of the role of imaging in tendon and muscle injury is given here.

Normal Tendon• On US, tendons are visualized

as linear structures comprising multiple parallel echogenic bands representing the interfaces between collagen bundles. Vascular flow is not shown in the normal tendon.

• Using MRI the normal tendon is visualized as a nonenhancing low signal structure on all conventional sequences.

Long head of biceps tendon shown on ultrasound. .

A word of caution!!!• Tendons are comprised of highly organized linear bundles of collagen microfibrils with an

extremely regular and ordered structure.• The regular structure results in an alteration in the imaging characteristics of tendons on US

depending on the tendon alignment relative to the ultrasound beam.

• This property is known as ANISOTROPY. • To see the normal echogenic fibrillar pattern in tendons on US the tendon must be aligned

perpendicular to the ultrasound beam. • Any significant angulation of the incident ultrasound beam to the tendon will result in echoes

generated by the tendon being reflected back at an angle and not returned to the transducer. This leads to the tendon appearing hypo- or even anechoic.

A word of caution!!!• The anisotropy of tendons on MRI is the result of the so-called ‘magic angle phenomenon’. • This can result in artefactual increased signal from tendons on short TE imaging sequences. • Normally tendons have an extremely short T2 relaxation time, giving them the signal void seen with conventional

MRI techniques. However, when the alignment of the tendon (and therefore the collagen bundles within it) approaches 55 degrees to the static magnetic field (B0), known as the magic angle, the T2 relaxation lengthens and signal is seen from within the tendon. This effect is only seen on short TE imaging sequences (T1 and proton density) and is important because tendon abnormalities usually yield increased signal from within the tendon on short TE imaging. Lesions can be distinguished from the magic angle effect by the persistence of abnormal signal on long TE sequences. The magic angle effect is not exclusive to tendons and may also be seen in ligaments, menisci and articular cartilage

Chronic tendon injury

• Chronic or repetitive trauma to a tendon results in degenerative change within the tendon which has become known as tendinopathy or tendinosis.

• Changes seen within the tendon include degeneration and disorganization of the collagen bundles along with vascular ingrowth.

Tendinopathic Tendons • Ultrasound

– thickening of the affected tendon.

– areas of low reflectivity will be seen within the tendon

– loss of the normal fibrillar architecture.

– Neovascularization may also be seen with Doppler techniques demonstrating blood flow within the normally avascular tendon

Patellar tendinopathy. (A) Longitudinal US shows the thickened patellar tendon

(between the arrowheads) at its insertion into the patella (P). Note the low reflective change within its substance.

(B) A similar section, this time with power Doppler, shows the intense neovascularization seen within the tendinopathic tendon. Normal tendon is avascular.

Tendinopathic Tendons

• MRI – thickening of the

affected tendon. – increased signal will be

seen within the tendon on both short and long TE sequences.

Patellar tendinopathy. Sagittal proton density MR image of the patellar tendon shows thickening and increased intrasubstance signal at its proximal insertion (arrow).

• Some tendons, such as the extensors and flexors of the hand and foot, have a synovial tendon sheath; where this becomes involved in the process the condition is known as tenosynovitis.

• Tenosynovitis will be seen on US and MRI as – synovial thickening and – fluid surrounding the

tendon.

• Many tendons do not have a tendon sheath (for instance the Achilles and patellar tendons) and are instead surrounded by loose connective tissue known as the paratenon. This may also become involved, a condition known as paratenonitis.

• Paratenonitis is seen – on US as a low reflective

‘halo’ surrounding the tendon and

– on MRI as a thin high signal rim on T2 imaging which enhances with gadolinium on T1 imaging.

• Calcific deposits may form within the tendon – demonstrated on conventional radiographs. – shown on US as bright reflective foci.– low signal on MRI although there may be increased

signal in the surrounding tissues due to inflammatory response.

– Tendon calcification can cause susceptibility artefact. – In acute calcium deposition the calcific material is

liquid or semiliquid and may show fluid–fluid levels on MRI.

Tendon tears

• Tendon tears are unusual in an otherwise normal tendon.

• When a tendon undergoes tendinopathic change it becomes weaker and at this point tears may occur.

Tendon tears - Full or partial thickness.

• Full thickness tears are generally easily recognized at US and MRI. – Retraction of the torn ends

will be seen– haematoma or fluid will be

seen filling the gap (depending on how acute the tear is).

• Assessment of the tendon dynamically with US helps confirm the full thickness nature of the tear.

• Disruption of a tendon without tendinopathic change is usually the result of avulsion of the tendon from the bone.

• In this case the avulsed bone fragment may be seen on conventional radiographs, but its tendon attachment can be confirmed at US or MRI.

Partial thickness tears

• The distinction between a partial thickness tear and tendinopathy may be difficult at US and MRI.

• US – well-defined low reflective areas or clefts

extending into the substance of the tendon, – Doppler will help distinguish a tear from vessels

formed in an area of tendinopathy.

Partial thickness tears

MRI presence of high signal on T2-weighted MRI extending to a tendon surface is also indicative of a partial thickness tear.

In general, studies would suggest that in many cases there is little to choose between MRI and

US when diagnosing tendon abnormalities

vs

Muscle injury • Muscle injuries are common,

especially in those undertaking athletic activities.

• Movement in muscle is transmitted to the skeleton through the kinetic chain comprising muscle connecting to tendon connecting to bone.

• The majority of ‘muscle’ tears in fact represent tears at the myotendinous junction where the tendon arises from the muscle, a relatively weak point in the kinetic chain.

myotendinous junction, a relatively weak point in the

kinetic chain.

Muscle Tears

• The diagnosis of muscle tears is normally a clinical one.

• Imaging can be helpful– indication of the degree of severity of the muscle

injury– Helpful in predicting the likely time before the

athlete can return to competition.

Acute muscle injury – Grade 1 • A grade 1 tear or strain

– microscopic tearing of muscle fibres, usually without loss of muscle strength.

– No macroscopic tear in the muscle fibres is seen

– oedema and haemorrhage may occur within the muscle.

• USG – – usually normal – occasionally a mild increase in reflectivity can

be seen.

• MRI – depend on the relative amount and age of

haemorrhage and oedema. – Majority appear as intermediate signal on T1

and increased signal on T2-weighted imaging. – poor relationship between the severity of the

patient's symptoms and the MRI findings

• Partial tears where there is macroscopic but incomplete separation of muscle or muscle and tendon.

• The muscle belly will be retracted at the site of the tear, opening a gap which will be filled with haematoma or fluid.

• USG / MRI – – Depending on the age of the tear the haematoma may appear anechoic or more

complex. – The demonstration of muscle retraction may be helped by examining the area

dynamically. – fluid tracking around the muscle adjacent to the covering fascia.

Acute muscle injury – Grade 2

Longitudinal extended field of view US demonstrates a grade 2 muscle tear of the medial head of gastrocnemius in a different patient. The retracted medial head of gastrocnemius muscle (G) is seen separated from the underlying tendon aponeurosis (arrow) and soleus muscle (S) by haematoma (H).

Grade 3 tears represent a full thickness tear of the muscle with complete separation of the torn ends of the muscle, or more commonly the muscle from the tendon.

Biceps brachii tendon tear. Longitudinal scan of the bicipital groove shows proximal retraction of the biceps muscle (long arrow). A fluid-filled gap with echogenic clots (small arrow) at the myotendinous junction.

Tendoachilles tear at the myotendinous junction.

Blunt trauma to a muscle

• Haemorrhage into the muscle (often with some swelling).

• Where muscles overlie each other, two or more muscles (or even muscle groups) may be involved.

• The diagnosis is normally clear from the history, but imaging will show haemorrhage and oedema within the muscle.

• This is often subtle on US and the characteristic finding is increased reflectivity and some focal swelling of the muscle.

Chronic muscle injuries

• Disuse atrophy of muscle may be seen from a variety of causes including chronic muscle or tendon injury and denervation.

• The loss of muscle bulk may be obvious on cross-sectional imaging. In addition the muscle undergoes a process of fatty infiltration seen as increased signal on T1-weighted MRI, as increased echogenicity on US, and as areas of fat attenuation on CT.

Delayed onset muscle soreness (DOMS)

• DOMS is a well-recognized phenomenon where muscular pain develops hours or days after muscle activity.

• It remains poorly understood but is manifest on MRI as oedematous change (increased signal on T2 weighting and STIR imaging) in the affected muscles.

• The appearances are therefore similar to those of a muscle strain, but the clinical picture differs in that the symptoms come on some time after the exercise.

• As with muscle strains, the MRI findings take longer to resolve than the muscular pain.

Myositis ossificans • Myositis ossificans may develop following

muscle trauma. • In this condition ossification occurs in the

muscle and may be visible on plain radiography and CT .

• Ultrasound will show the area of ossification as a dense reflection from within the muscle with posterior acoustic shadowing.

• MRI initially shows oedema-type change in the muscle. This gradually organizes, becoming better defined. Cortical bone developing around the edges of the lesion is of low signal intensity on all sequences. In the mature lesions the centre of the area becomes filled with bone trabeculae surrounded by fatty bone marrow. The latter will show signal characteristics of fat.

Early peripheral mineralization.

Six weeks later there has been maturation with well-organized peripheral ossification

Muscle hernias • Muscle hernias usually present as a

lump which the patient may notice becomes more prominent when the muscle is tensed. They represent muscle fibres herniating out through a tear or weakness in the muscular fascia. Such weaknesses are often associated with perforating veins in the lower limb.

• Ultrasound during muscle contraction is readily able to show muscle hernias and provide reassurance that the palpable mass is composed of normal muscle tissue. Tibialis Anterior – muscle hernia

Soft Tissue Tumors

Soft Tissue???

• Soft tissue – derived primarily from mesenchyme and – consists of • skeletal muscle, • fat, • fibrous tissue, • the vascular structures• the peripheral nervous system.

General Concepts

• Soft-tissue tumors are classified histologically on the basis of the adult tissue they resemble.– Eg: liposarcoma does not indicate a lesion arose from fat, but

rather that it is a malignant mesenchymal tumor that has differentiated into tissue that microscopically resembles normal adult fat.

• Many sarcomas are poorly differentiated and, consequently, lack the microscopic features required to make a specific diagnosis.

• In such cases, immuno-histochemical stains have aided pathologists in identifying their pattern of differentiation, allowing accurate classification.

General Concepts

• Soft-tissue sarcomas– relatively uncommon and are estimated to

represent about 1% of all malignant tumors.– two to three times as common as primary

malignant bone tumors.• The annual clinical incidence of benign soft-

tissue tumors is estimated at 300 per 100,000, and these tumors are about 100 times more common than malignant soft-tissue tumors.

The World Health Organization (WHO)

classification system for soft-tissue tumors

Additional soft-tissue lesions are not included in the WHO classification

A SYSTEMATIC APPROACH FOR CHARACTERIZATION OF SOFT-TISSUE MASSES

• Given the wide variety of masses and the overlap that exists between the imaging characteristics of benign and malignant masses, it is impossible to arrive at a single diagnosis for many of the lesions encountered.

• By applying a systematic approach, one – can arrive at a diagnosis for the subset of lesions that have

characteristic appearances and – can narrow the differential diagnosis for lesions that

demonstrate indeterminate characteristics. • In the appropriate clinical setting, excluding a benign

diagnosis (eg, lipoma or ganglion) can aid in clinical decision making.

• Ultimately, if a lesion cannot be characterized as a benign entity, the lesion should be reported as indeterminate and the patient should undergo biopsy to exclude malignancy.

Then what is the role of imaging?

Clinical History and Physical Examination

• Evaluation of a soft-tissue mass begins with the clinical history and physical examination.

• Clinical history regarding – age, – recent trauma, – fluctuating mass size, – history of malignant cancer

and familial syndromes, – single or multiple lesions

Clinical History and Physical Examination

At physical examination, determining whether the• mobile or fixed.

– In general, masses that are mobile are more suggestive of a benign diagnosis, while masses that are fixed to surrounding tissues are more suggestive of malignancy.

• skin changes – such as ecchymosis related to

trauma or inflammatory changes from cellulitis and soft-tissue abscess, can aid in establishing an appropriate differential diagnosis.

Location

• Certain masses occur in specific locations in the body, aiding in lesion characterization.

Origin of the lesion

• Recognizing that a lesion arises from a specific structure (eg, nerves, vessels, or tendons) can help in lesion characterization.

• Tumors arising from nerves are typically benign PNSTs, which include schwannomas and neurofibromas. If there is a history of type 1 neurofibromatosis, a malignant PNST should be considered. Occasionally, fat-containing tumors can also arise from nerve. This type of lesion, previously known as a fibrolipomatous hamartoma, has been designated as lipomatosis of the nerve by the WHO in the 2002 classification.

• Vascular neoplasms typically have dilated tortuous vessels entering and/or exiting the lesion and include hemangiomas, lymphangiomas, and angiosarcomas . Hemangiomas are the most common of the vascular lesions and contain serpentine vessels, areas of fat, and phleboliths. Besides true vascular tumors, several additional vascular lesions should be included in the differential diagnosis of a soft-tissue mass arising from vessels. Pseudoaneurysms can occur in the setting of trauma, such as femoral vessel injury from cardiac catheterization. In these cases, it is important to make the diagnosis prospectively and to avoid biopsy. Another group of masses characteristically arise from tendon sheaths.

• Lesions arising from tendons are most commonly GCTs of the tendon sheath; however, ganglia, lipomas, and fibromas are all masses that may arise from a tendon sheath.

IMAGING

Radiography

• The radiologic evaluation of a suspected soft-tissue mass must begin with the radiograph.

• Radiographs may be diagnostic of a palpable lesion caused by an underlying skeletal deformity (such as exuberant callus related to prior trauma) or exostosis, which may masquerade as a soft-tissue mass.

• Radiographs may also reveal soft-tissue calcifications, which can be suggestive and, at times, very characteristic of a specific diagnosis. – phleboliths within a hemangioma , – juxtaarticular osteocartilaginous

masses of synovial chondromatosis,

– peripherally more mature ossification of myositis ossificans, or

– characteristic bone changes of other processes with associated soft-tissue involvement.

• When not characteristic of a specific process, soft-tissue calcification can suggest certain diagnoses. – nonspecific dystrophic

calcifications in a slowly growing lower extremity mass in a young adult should suggest a synovial sarcoma as the diagnosis of exclusion.

17-year-old girl with synovial sarcoma of footwho presented with slowly growing painless mass.

• In addition, radiographs are the best initial method of assessing coexistent osseous involvement, such as remodeling, periosteal reaction, or overt osseous invasion and destruction.

• However, unlike bone tumors, the biologic activity of a soft-tissue mass cannot be reliably assessed by its growth rate. A slowly growing soft-tissue mass that may remodel adjacent bone (causing a scalloped area with well-defined sclerotic margins) may still be highly malignant on histologic examination.

• A soft-tissue mass may also be the initial presentation of a primary bone tumor or inflammatory process. – In such cases, the radiograph may be useful in identifying the

osseous origin of the lesion. The diagnosis of a malignant bone tumor such as Ewing's sarcoma or primary lymphoma of the bone should be considered when there is a large circumferential soft-tissue mass in association with an underlying destructive permeative bone lesion.

• A subtle radiologic feature, which may help to separate inflammatory and neoplastic processes, is that an inflammatory process typically obliterates fascial planes rather than displaces them.

Role of CT• CT may be a useful adjunct in

specific circumstances. • We generally reserve CT for

patients in whom radiographs do not adequately depict the lesion, its pattern of mineralization, or its relationship to the host.

• This inadequacy typically occurs in areas in which the osseous anatomy is complex, such as the pelvis, shoulder, and paraspinal regions.

MR Imaging• MR imaging has emerged as the preferred modality for evaluating

soft-tissue lesions.• It provides

– superior soft-tissue contrast, – allows multiplanar image acquisition, – its capability in imaging superficial and deep soft tissues over both large

and small fields of view– obviates iodinated contrast agents and ionizing radiation, and – is devoid of streak artifacts commonly encountered with CT.

• Although initial investigations maintained that CT was superior to MR imaging in detecting destruction of cortical bone, later studies suggest that these two modalities are comparable in this regard.

• Evaluation with MR images allows – tumor staging, – detection of neurovascular involvement, – identification of tumor necrosis, and – preoperative planning.

Newer Techniques

• The use of techniques such as MR spectroscopy and diffusion imaging has been reported for the evaluation of soft-tissue masses and, in particular, for assessing response to therapy.

• These techniques offer intriguing potential for interrogation of soft-tissue masses but are not yet in routine clinical use.

• The utility of MR imaging in the assessment of soft-tissue masses is predicated on the generation of diagnostic images of good quality.

• A brief discussion of technical considerations as they relate to MR imaging of soft-tissue masses is therefore presented.

TECHNICAL CONSIDERATIONS FOR MR IMAGING OF SOFT-TISSUE MASSES

General Considerations

• Given the variety of sizes and locations of soft-tissue masses, it is difficult to prescribe a single imaging protocol.

• The lesion should be demarcated prior to imaging, but care should be taken not to compress or distort the mass, either with the skin markers or by imaging the mass dependently against the table.

• Images should be of sufficiently high spatial resolution to demonstrate relevant morphologic features and local anatomic detail.

Imaging Plane

• Lesions should be imaged in at least two orthogonal planes, using conventional T1-weighted and T2-weighted spin-echo MR pulse sequences in at least one of these planes.

• Axial images – For demonstrating relevant anatomy and – helping to determine whether the mass is confined to a single

compartment and – whether it is invading or encasing surrounding structures.

• Longitudinal plane—coronal, sagittal, or oblique– help demonstrate the extent of the mass and – its relationship to anatomic landmarks.

Imaging Strategy

• Field of view is dictated by the size and location of the lesion.

• large field of view– where the goal is to establish the presence of a mass.– sacrificing spatial resolution.

• smaller field of view– where detailed assessment of the mass is needed– delineate its features and – assess its proximity to surrounding structures.

Imaging Sequences

• Standard spin-echo MR images are most useful in establishing a specific diagnosis.– the most reproducible technique – the most often referenced in the tumor imaging literature. – the imaging technique with which we are most familiar for

tumor evaluation, – established as the standard by which other imaging

techniques must be judged. • The main disadvantage of spin-echo MR imaging remains

– the relatively long acquisition times, especially for double-echo T2-weighted MR imaging sequences .

• Fast scanning techniques may be useful in the evaluation of soft-tissue masses. – shorter imaging times, – decreased motion artifacts, and – increased patient tolerance, as well as patient throughput.

• Gradient-echo imaging may be a – useful supplement in revealing hemosiderin because of

the greater magnetic susceptibility of hemosiderin. – showing the lesion—fat interfaces and – depicting small surrounding vessels.

27-year-old woman with foreign body and associated abscess.

A, Oblique radiograph of foot shows irregular opacity (arrow ), initially

interpreted as calcification.B, Coronal T1-weighted spin-echo MR

image (600/15, TR/TE) shows prominent signal void (asterisk ), with “parenthetic”

artifact, compatible with foreign body.C, Corresponding conventional T2-

weighted spin-echo MR image (2500/80) shows foreign body (asterisk ) with associated inflammatory change.

D, Gradient-echo MR image (15/12, 15° flip angle) shows “blooming” (asterisk )

caused by greater magnetic susceptibility.

• STIR imaging can be an adjunct in selective cases. – produces fat suppression and – enhances the identification of abnormal tissue with

increased water content and, – as a result, is useful to confirm subtle areas of soft-

tissue abnormality– increases lesion conspicuity

• but – lower signal-to-noise ratio – more susceptible to degradation by motion.

• Fat suppression on T2-weighted MR images– increase lesion-to-background signal intensity differences for

high-signal-intensity lesions within the marrow or fatty soft tissue.

– decreasing or eliminating the MR signal from fat, – allowing increased conspicuity of lesions containing

paramagnetic substances (such as methemoglobin) on T1-weighted MR images, and

– revealing contrast enhancement. • However

– decreases variations in tumor signal intensities, and hence not used in place of conventional T2-weighted MR imaging.

Describing Masses

• The SI of masses should be described in relation to an internal standard.

• Most often, a mass is described as being hypo-, iso-, or hyperintense to muscle on both T1- and T2-weighted images.

• Some authors describe the SI of a mass on T2-weighted images in relation to subcutaneous fat; however, the relative SI of fat differs between SE and fast SE techniques.

MR Imaging Contrast Enhancement

• controversial. – enhance the signal intensity of many tumors on T1-weighted spin-echo MR

images, – enhancing the demarcation between tumor and muscle and tumor and edema – providing information on tumor vascularity.

• In actuality, differentiation between tumor and muscle is usually quite well delineated without contrast-enhanced imaging on T2-weighted MR images, and

• the accurate distinction between tumor and edema is probably of little practical value. Edema, which is infrequent without superimposed trauma or hemorrhage, is considered to be part of the reactive zone around the neoplasm and, as a result, is removed en bloc with the tumor.

• Disadvantages:– increases the length and cost of the examination. – not been shown to increase lesion conspicuity or

to replace conventional T2-weighted MR imaging . – contrast reaction (even though small)

• Consequently, gadolinium-enhanced imaging should be reserved for cases in which the results would influence patient care.

Contrast: Useful situations

• evaluation of hematomas. – may reveal a small tumor nodule that may have

been inapparent within the hemorrhage on conventional MR imaging.

Caution is required, however, because the fibrovascular tissue in organizing hematomas may show enhancement.

Contrast: Useful situations….

• differentiate solid from cystic (or necrotic) lesions or • identify cystic or necrotic areas within solid tumors, – these necrotic or cystic areas showing no enhancement. In general, sonography is fast and inexpensive and is an

ideal method for differentiating solid and cystic lesions when the lesion is in an anatomic location accessible to sonographic evaluation.

• guide biopsy

Contrast: Useful situations….

• Evaluation of tumor recurrence

Enhancing tumor nodule in a post operative desmoid tumor, suggestive of recurrence

Technical considerations in contrast imaging

• Intravenous gadolinium-based contrast agent is generally administered in a nondynamic fashion.

• Contrast-enhanced images are often obtained with fat suppression to suppress fat and highlight the presence of the gadolinium-based contrast agent.

Technical considerations…..In choosing to use fat-suppressed T1-weighted MR sequences for this purpose, several considerations apply:1. Images obtained before and after contrast agent administration must be

obtained with identical imaging parameters to allow adequate assessment of enhancement.

2. For similar reasons, transmit gain cannot be allowed to change between nonenhanced and contrast-enhanced images. To maintain the same transmit gain, no preliminary imaging should take place between nonenhanced and contrast-enhanced imaging.

3. If, on nonenhanced images, fat suppression proves to be inhomogeneous, consideration should be given to acquiring the nonenhanced and contrast-enhanced images without fat suppression.

4. Image subtraction can help to address the problem of inhomogeneous fat suppression, but this technique depends on the absence of patient motion between the nonenhanced and contrast-enhanced sequences.

LESION CHARACTERIZATION ON THE BASIS OF MR IMAGES

T1 Hypo- or Isointense Lesions

• Most soft-tissue masses are iso- or hypointense to muscle on T1-weighted images; – limited ability to distinguish or characterize lesions on the

basis of low T1 SI alone. • The differential diagnosis for these masses is extensive

and includes both benign and malignant lesions. – For example, ganglia, fibrosarcomas, and pleomorphic

sarcomas can all demonstrate T1 hypo- or isointensity. • Lesions that are iso- or hypointense to muscle on T1-

weighted MR images should be further evaluated with T2-weighted MR images.

T1 Hyperintense Lesions

• Higher in SI than skeletal muscle on T1-weighted images.

• SI should be determined on images that are obtained without fat suppression because some masses may be isointense to muscle on T1-weighted images without fat suppression but relatively hyperintense to muscle on fat-suppressed T1-weighted images.

T1 Hyperintense…..• Substances that are associated with T1 shortening include

– fat, – methemoglobin, – proteinaceous fluid, and – melanin

• Fat has intrinsically short T1 relaxation times due to its molecular structure. • Methemoglobin causes shortening of T1 relaxation times due to a

paramagnetic effect. • Proteinaceous fluid is characterized by relative T1 shortening due to

accelerated relaxation of water molecules bound to proteins . • Although one report of T1 shortening in melanomas ascribed the effect

directly to paramagnetic radicals associated with melanin itself, a later report theorized that it was owing to other sources, such as biological paramagnetic metals that become bound by the melanin.

• If the mass has areas of hyperintense T1 signal, the next step is to evaluate suppression on fat-suppressed T1-weighted images. – It is important to perform the sequence with

frequency-selective (also known as chemically specific) fat suppression.

– Inversion-recovery fat suppression is nonspecific and can cause loss of signal of not only fat but also of other short-T1 substances.

Fat suppression +

• If the hyperintense area is suppressed, then the lesion contains fat, and the most likely diagnoses include – lipoma, – lipoma variant, – well-differentiated liposarcoma, – hemangioma, and – mature ossification.

Fat suppression +

• If the mass is composed entirely of fat, with only minimal thin septations and without nonfatty nodular components, then a diagnosis of lipoma can be made.

If the lesion is greater than 10 cm in diameter, contains septa greater than 2 mm thick and/or globular or nodular nonfatty

components, or is comprised of less than 75% fat, then a diagnosis of well-differentiated liposarcoma is likely.

59-year-old woman with well-differentiated liposarcoma.

Fat suppression +

• Some lipomatous masses, including some lipomas and lipoma variants, have a complex appearance because they contain benign soft-tissue constituents; thus, it may be difficult to distinguish these entities from well-differentiated liposarcomas.

28-year-old woman with chondroid lipoma. Sagittal T1-weighted image (TR/TE, 600/10) obtained through left chest shows mass posteriorly, which is predominantly high in signal but contains nodular foci of low signal (arrow).

Fat suppression +

• Hemangiomas with fatty components will have suppressed SI on fat-suppressed MR images but should have a distinct appearance from lipomas.– lobulated – have high-SI vascular channels on T2-weighted MR

images (due to slow intravascular flow), – may contain rounded low-SI phleboliths on T1- and T2-

weighted MR images, (more apparent on radiographs) – may cause fatty atrophy in surrounding muscles or

reactive sclerosis in abutting bones.

10-year-old boy with hemangioma of lower extremity. • Axial T1-weighted MR image (TR/TE, 500/16) shows low signal

intensity of tumor (arrows) with interspersed areas of high signal intensity representing fat.

• Axial T2-weighted MR image (4000/85) shows lobulated high-signal-intensity lesion. Note several central low-signal-intensity dots (arrows).

• Gadolinium-enhanced T1-weighted MR image (500/16) shows marked enhancement of lesion. Central low-intensity dots seen on B are not seen after contrast administration, suggesting vascular nature.

Fat suppression + • Ossification, seen with mature

myositis ossificans or heterotopic ossification, can appear to be T1 hyperintense owing to fatty marrow.

• Again, reviewing the radiographs for evidence of mature ossification is helpful; however, ossification may not be apparent on radiographs, especially in the early stage of myositis ossificans.

• In these cases, CT images may be helpful for identifying early mineralization.

Mature (late) myositis ossificans in popliteal fossa of a man 35 years of

age. A: Radiograph shows a densely mineralized mass in the popliteal fossa. B: Axial CT scan displayed at bone window shows irregular diffuse mineralization throughout the mass. The attenuation coefficient of the nonmineralized area is difficult to assess, but areas imaging similar to fat can be seen. C,D: Axial T1-weighted (C) and T2-weighted (D) spin-echo MR images show a well-defined mass (arrows) in the popliteal fossa. Areas of increased signal within mass (asterisk) have a signal intensity similar to that of subcutaneous fat.

Fat suppression (-)

• If the lesion does not lose SI on the fat-suppressed T1-weighted MR images, then it is composed of another substance that causes T1 shortening, such as – methemoglobin, – proteinaceous fluid, or – melanin.

Fat suppression (-)

• A history of trauma may account for a hematoma with methemoglobin.

• However, a hematoma might also occur secondary to bleeding from a tumor.

• So a hematoma should be followed up with imaging to resolution to exclude an underlying sarcoma or other malignant lesion as the source of the hematoma.

8-year-old woman with subacute hematoma adjacent to lipoma.

T1-weighted axial image shows subacute hematoma (white arrow) with relatively increased signal intensity due to extracellular hemoglobin. Compare hematoma with higher signal intensity mass (black arrow), which is lipoma.

T1-weighted fat-suppressed MR image shows that signal intensity of subacute hematoma (white arrow) remains bright, whereas that of lipoma (black arrow) “drops out.”

Fat suppression (-)

• Any mass containing sufficient fluid with an appropriate concentration of protein can have high T1 SI.

• These masses include ganglia, abscesses, and epidermoid inclusion cysts with high protein content.

Fat suppression (-)

• If the patient has a history of melanoma and a mass with high T1 SI, the possibility of a melanoma metastasis should be considered

• It should be noted, however, that not all melanotic lesions are characterized by substantial T1 shortening .

T2 Hypointense Lesions

• A mass that is lower in SI than skeletal muscle on T2-weighted MR images is considered to be hypointense .

• Substances that appear hypointense on T2-weighted images include – fibrosis, – hemosiderin, and – calcification (distinct from ossification).

T2 Hypointense….• Lesions with fibrotic components tend to have low T2 SI because of a relative

lack of mobile protons associated with their hypocellular densely collagenous matrix.

• Hemosiderin, a nonspecific end-product from the breakdown of hemorrhage, is T2 hypointense due to magnetic susceptibility. When present in sufficient quantities, hemosiderin can appear more prominent (blooming) on T2*-weighted MR images than on T2-weighted MR images .

• Calcifications are typically T2 hypointense because the protons are immobilized within a crystalline structure and cannot contribute to the signal. Paradoxically, calcifications may appear as higher SI when calcium crystals are

surrounded by a hydration shell, which provides a source of mobile protons .

• Substances that have intrinsic low proton density, such as air and some foreign bodies, also can appear to be T2 hypointense. Foreign bodies can be deceptive, as small foreign bodies may be surrounded by a

hyperintense area from reactive fluid or inflammatory tissue, which can obscure the underlying foreign body and mimic a neoplasm.

• Masses that are composed of fibrotic material represent – broad spectrum of benign and malignant lesions, – ranging from fibrotic scars to fibromas and some fibrosarcomas.

• T2 hypointensity in lesions such as GCT of the tendon sheath, amyloid deposits, long-standing rheumatoid pannus, soft-tissue callus, leiomyoma, and lymphoma has been ascribed to the presence of hypocellular fibrosis.

However, not all fibrous masses have low T2 SI; hypercellular fibrous masses, such as desmoids and leiomyomas, may demonstrate higher T2 SI.

Masses that contain large amounts of hemosiderin include pigmented villonodular synovitis, GCT of the tendon sheath, and a variety of hemorrhagic masses.

• Masses that are diffusely calcified may also appear to have low T2 SI.

• However, the SI will depend on – the extent and distribution of calcification, – whether the calcification is hydrated, and – whether there is associated edema or

inflammatory reaction

mass with low T2 SI

• first step is to review the radiographs for the presence of calcifications, which are often difficult to identify on MR images alone.

• On radiographs, calcifications may have a characteristic pattern, such as the – cloudlike paraarticular calcifications seen in gout

or – the flocculent calcifications seen in tumoral

calcinosis.

• If there are no calcifications on the radiographs, then a mass with low T2 SI will most likely either be focal fibrosis or a tumor with substantial fibrous content.

• In these cases, lesion location can be helpful for further characterization. – Single or multiple masses within a joint may reflect the presence of pigmented

villonodular synovitis. – Similarly, if a well-circumscribed noncalcified mass abuts a tendon, it may be a

GCT of the tendon sheath. – A history of prior surgery at the lesion site could suggest the presence of fibrous

scar tissue. – A nodular mass that is adjacent to the plantar fascia of the foot most likely is a

plantar fibroma. – Similarly, a mass along the superficial palmar fascia of the hand can suggest

Dupuytren disease.

T2 Hyperintense (Cystlike) Lesions

• Many T2 hyperintense lesions are heterogeneously hyperintense.– difficult to specifically characterize.

• A subset of lesions that are relatively homogeneously hyperintense – can be further characterized.

T2 hyperintense…..

• Thus, the differential diagnosis for lesions that are predominantly T2 hyperintense includes – fluid-filled lesions (eg, ganglia, synovial cysts, and

seromas) – solid lesions (eg, myxomas, myxoid sarcomas, some

PNSTs, and small synovial sarcomas). • Some are relatively homogeneous hyperintense, • mistaken for fluid-filled structures • have been termed cystlike lesions by some authors.

– hyperemic synovium and – hyaline cartilage.

True Cysts vs Cyst like lesions• Administering an intravenous gadolinium-based contrast agent is an

important step to distinguish between true cysts and solid lesions. • Cysts and fluid-filled components of masses

– will NOT demonstrate internal enhancement whereas • solid (Cyst like) structures

– will usually demonstrate internal enhancement.

• Note!!! – given sufficient time, gadolinium-based contrast agents can diffuse into the center

of a cyst from the periphery. – Thus, internal enhancement can be seen in a true cyst if it is imaged late after

contrast agent administration . – Although there are no well-formulated rules for this phenomenon, we typically

evaluate enhancement on MR images obtained within 6 minutes after contrast agent administration.

Peripheral enhancement

• If a T2 hyperintense mass has a thin even rim of enhancement and no internal enhancement, then it is a cyst of some kind. – Ganglia are very common and should be considered whenever a

periarticular hyperintense mass is identified on T2-weighted MR images.

– Postoperative seromas, posttraumatic cysts, epidermoid inclusion cysts, lymphoceles, and lymphangiomas are other lesions that may demonstrate a thin rim of peripheral enhancement .

• When the peripheral rim of enhancement is thick and/or irregular, – other diagnoses must be considered, including inflamed or

infected ganglia, abscesses, hematomas, and necrotic tumor masses.

Internal enhancement

• If a mass that is T2 hyperintense demonstrates internal enhancement, either homogeneous or heterogeneous, then soft-tissue masses (eg, intramuscular myxomas, myxoid sarcomas, PNSTs, and synovial sarcomas) should be considered.

• Myxoid material because of its high water content appears hyperintense on T2-weighted MR images.

Lesions showing internal enhancement…..

• Intramuscular myxomas – benign masses – typically have uniform hyperintensity on nonenhanced T2-weighted MR images – demonstrate internal enhancement on contrast-enhanced MR images.

• Myxoid sarcomas – can be homogeneously T2 hyperintense but also – demonstrate internal contrast enhancement.

• Synovial sarcoma should be considered– an enhancing hyperintense lesion is paraarticular. – Irregular calcifications, erosion of the bone, and cystic components may be

associated. • PNST is suggested

– lesion is fusiform and – is associated with a nerve

Axial fat-suppressed MR images in 56-year-old woman show palpable lesion in groin. (a) T2-weighted MR image shows a hyperintense cystlike lesion (arrow) in the left upper thigh.(b) Nonenhanced T1-weighted SPGRMRimage at level of lesion (arrow). (c) Contrast-enhanced T1-weighted SPGRMR image shows wispy internal enhancement

(arrow). Intramuscular myxoma was identified at biopsy.

Benign Versus Malignant

• Diagnostic value of MR imaging – general agreement

• Reliably distinguish benign from malignant???– less clear.

• When not sufficiently characteristic to suggest a specific diagnosis, – a conservative approach is warranted.

• Malignancies are generally – larger and – more likely to outgrow their vascular supply with subsequent

infarction, necrosis, and heterogeneous signal intensity on T2-weighted spin-echo MR imaging.

• Consequently, the larger a mass is, the greater its heterogeneity, the greater is the concern for malignancy. – Only 5% of benign soft-tissue tumors exceed 5 cm in diameter. – Only about 1% of all benign soft-tissue tumors are deep.

• Superficial sarcomas have less aggressive biologic behavior than do deep lesions.

• As a rule, most malignancies grow as – deep space-occupying lesions, – enlarging in a centripetal fashion, – pushing rather than infiltrating adjacent structures (although clearly

there are exceptions to this general rule). – as sarcomas enlarge, a pseudocapsule of fibrous connective tissue is

formed around them by compression and layering of normal tissue, associated inflammatory reaction, and vascularization.

– generally, they respect fascial borders and – remain within anatomic compartments until late in their course.

• It is this pattern of growth that gives most sarcomas relatively well-defined margins, in distinction to the general concepts of margins used in the evaluation of osseous tumors.

• Metastatic carcinoma to soft tissue – appear more infiltrative with ill-defined margins – often violating fascial planes and anatomic

compartments. • This pattern of growth is quite different from

that seen in most primary soft-tissue tumors.

• Increased signal intensity in the skeletal muscle surrounding a musculoskeletal mass on T2-weighted spin-echo MR images or other fluid-sensitive sequences (i.e., STIR) – suggested as a reliable indicator of malignancy. – quite nonspecific. – more commonly suggests an inflammatory process,

abscess, myositis ossificans, local trauma, hemorrhage, biopsy, or the effect of radiation therapy rather than a primary soft-tissue neoplasm.

14-year-old boy with myositis ossificans in forearm.

A, Axial fast spin-echo T2-weighted spin-echo MR image (2600/80, TR/TE) shows poorly defined mass in extensor compartment of forearm and adjacent to ulna. Lesion predominantly involves extensor carpi ulnaris, although there is abnormal signal in and between adjacent muscles.B, Corresponding axial T1-weighted spin-echo MR image (650/20) shows only minimal signal alteration witheffacement of subcutaneous adipose tissue (arrow )

Benign vs Malignant - Role of Gadolinium

• Malignant lesions show – greater enhancement as well as – greater rate of enhancement.

• Enhancement reflects tissue vascularity and tissue perfusion.

• Considerable overlap – little practical value.

• When a lesion has a nonspecific MR imaging appearance, one is ill-advised to suggest a lesion is benign or malignant solely on the basis of its MR imaging characteristics and rate or degree of enhancement.

• DeSchepper et al. performed a multivariate statistical analysis of 10 imaging parameters, individually and in combination.

• Highest sensitivity for malignancy – high signal intensity on T2-weighted MR images, – larger than 33 mm in diameter, – heterogeneous signal intensity on T1-weighted MR images.

• Greatest specificity for malignancy – tumor necrosis, – bone or neurovascular involvement, and – mean diameter of more than 66 mm

15-year-old girl with rhabdomyosarcoma of leg.A, Sagittal T1-weighted spin-echo MR image shows large mass with bone invasion.B, Corresponding contrast-enhanced MR image shows nonenhancing area compatible with necrosis. Bone invasion and necrosis are both specific for malignancy. Note nodal involvement (arrows ).

57-year-old woman with liposarcoma of thigh.A, Axial fast spin-echo T2-weighted MR image (3200/102, TR/TE) shows large mass with mixed intermediate signal intensity.B and C, Corresponding coronal unenhanced (B) and contrast-enhanced (C) T1-weighted spin-echo MR images (600/16) show adipose tissue within lesion, compatible with fat differentiation. Enhancement in portions of tumor is extensive. Large size and deep location with adipose differentiation suggest diagnosis of liposarcoma.

Staging

• Purpose of a staging system – the state of a malignancy, – defining the extent of the local and distant tumor – critical for optimum patient care and – planning of percutaneous biopsy.

• Local staging is best accomplished using MR imaging, which can accurately depict the anatomic spaces (compartments) involved by the tumor.

The Indeterminate Lesion

• Identify the lesion as a benign determinate lesion. • Provide a succinct differential diagnosis on the basis

of the available characteristics. • However, if the lesion cannot be confidently

characterized as a benign entity, then it is an indeterminate lesion and requires further evaluation.

• This concern should be discussed with the ordering clinician, and a biopsy should be strongly considered.

The Indeterminate Lesion

• The WHO recommends that • “soft tissue masses that do not demonstrate

tumor-specific features on MR images should be considered indeterminate and biopsy should always be obtained to exclude malignancy”.

• In some instances, especially in patients with comorbidities or relative contraindications to biopsy, short-term imaging follow-up may be an alternative.

Conclusion• MR imaging is the preferred modality for the evaluation of a soft-tissue

mass after radiography. • The radiologic appearance of certain soft-tissue tumors or tumorlike

processes, such as myositis ossificans, fatty tumors, hemangiomas, peripheral nerve sheath tumors, pigmented villonodular synovitis, and certain hematomas may be sufficiently unique to allow a strong presumptive radiologic diagnosis.

• It must be emphasized that MR imaging cannot reliably distinguish between benign and malignant lesions

• When radiologic evaluation is nonspecific, one is ill-advised to suggest that a lesion is benign or malignant solely on its MR imaging appearance.

• When a specific diagnosis is not possible, knowledge of tumor prevalence by location and age, with appropriate clinical history and radiologic features, can be used to establish a suitably ordered differential diagnosis.