ULTRASONOGRAPHIC EVALUATION OF BRACHIAL PLEXUS

TUMORS IN FIVE DOGS

SCOTT ROSE, CRAIG LONG, MARGUERITE KNIPE, BILL HORNOF

Five dogs with unilateral thoracic limb lameness, neurologic deficits, muscle atrophy, and pain, or a combination

of these signs, were examined using ultrasonograghy. Large, hypoechoic tubular masses that displaced vessels

and destroyed the normal architecture were found in each dog. The affected axilla of each patient was then

imaged with computed tomography or magnetic resonance to fully assess the extent of the masses. We describe

the use of ultrasound in screening patients for brachial plexus tumors. Veterinary Radiology & Ultrasound,

Vol. 46, No. 6, 2005, pp 514–517.

Key words: brachial plexus, peripheral nerve sheath tumor, tumor, ultrasound.

Introduction

THE MOST COMMON tumors of the brachial plexi in dogs

are peripheral nerve sheath tumors. These primary

tumors most commonly involve the spinal nerve roots in

the caudal cervical and cranial thoracic spinal cord and the

nerves contributing to the brachial plexus.1–6 Most often

these tumors arise from the Schwann cells or fibroblasts

within nerve epineurium or endoneurium. A variety of no-

menclature has been assigned to these tumors including:

neurofibromas, neurofibrosarcomas, schwannomas, malig-

nant schwannomas, neurolemmomas, neuronomas, and

perineural fibroblastomas. These terms have been compiled

into a broader category of peripheral nerve sheath tumors.7

In addition to peripheral nerve sheath tumors, primary

tumors of other tissues within the brachial plexus (e.g.,

rhabdomysosarcoma, osteosarcoma, etc.) and secondary

tumors can affect the brachial plexus.

Survey radiography, myelography, electromyography

(EMG), computed tomography (CT), and magnetic reso-

nance (MR) imaging are commonly used to detect brachial

plexus tumors.4,6,8 Radiography is poorly sensitive and

poorly specific for detecting brachial plexus tumors. Al-

though myelography can improve tumor detection when

the tumor involves the vertebral canal, the potential for

false negative studies is still very high.4,8 Myelography is

ineffective for tumors outside the vertebral canal. EMG

electrical activity may be abnormal in affected muscles, but

this is not specific for a tumor.6,7 Contrast-enhanced CT

and MR imaging provide excellent detail of the brachial

plexus and associated masses.4,8,10 These modalities are ul-

timately the best tools in veterinary medicine to image

peripheral nerve sheath tumors.8

Ultrasound examination (US) of the canine axilla has

not been used routinely to detect brachial plexus tumors

despite the ability to image masses and differentiate them

from the surrounding vasculature. We began to routinely

image the axillae of dogs with unexplained thoracic limb

lameness to determine if peripheral nerve sheath tumors

can be detected. We describe five dogs with a brachial

plexus tumor detected with ultrasound.

Materials and Methods

We evaluated patients presenting or referred to the

Veterinary Medical Teaching Hospital (VMTH) with pro-

gressive lameness and neurologic deficits affecting one tho-

racic limb. These patients had no signs of osteopathy or

arthropathy and those dogs treated with medication for

arthritis did not respond to the treatment. Five patients

with recorded images of the brachial plexus tumors were

selected for description in this paper.

The brachial plexus region was imaged by placing a

5–8MHz curvilinear or linear transducer� in the shaved

axillary region, medial to the scapulohumeral joint and

cranial to the first rib. The patients were scanned in ventral

recumbency and the affected limb was fully extended and

abducted 30–451. The axilla was interrogated with the

probe sagittal to the patient but transverse to the long axis

of the limb.

In the normal patient the largest identifiable structure is

the axillary vein followed by the axillary artery (Fig. 1). If

the vessels are scanned more distally the axillobrachial vein

can be visualized alongside the axillary artery. Veins can be

distinguished from arteries by their flow on color Doppler

(towards the scan plane), their slower flow (also determined

Address correspondence and reprint requests to Craig Long, DVM, atthe above address.E-mail: cdlong@ucdavis.edu

Received September 15, 2004; accepted for publication May 11, 2005.doi: 10.1111/j.1740-8261.2005.00093.x

School of Veterinary Medicine, Surgical and Radiological Sciences,2112 Tupper Hall, Davis, CA 95616.

�HDI 5000, Philips Medical Systems, Bothell, WA.

514

with Doppler), their larger size, and their compressibility

with increased transducer pressure. Arteries are distin-

guished by high velocity flow on color Doppler and visible

pulsations.

The most caudal of the radices plexi, the ventral spinal

nerves that contribute to the brachial plexus,9 run along-

side and deep to the axillary artery and vein and can be

seen in the normal dog as a small (2–3mm) linear structure

(Fig. 1). Nerve sheath tumors in the brachial plexus were

visible as large tubular, hypoechoic structures, which

lacked flow, and caused the axillary artery to deviate from

the vein (Figs. 2 and 3).

Once the plexus was imaged in the transverse plane, the

probe was rotated 901 counterclockwise on its axis to vis-

ualize the vasculature and nerves in longitudinal section.

Again, the axillary vein was the largest vessel and the rad-

ices plexi travel alongside (Fig. 4). It was more difficult to

detect blood flow with color Doppler when the vasculature

was perpendicular to the transducer. Rotating the probe on

its axis so that the vessels obliquely crossed the scanning

field helped distinguish vessels from tumor. The tumors

looked very similar to vessels in this plane, appearing as

tubular, hypoechoic structures but they lacked the hyper-

echoic vessel wall and blood flow (Fig. 5). Tumors involv-

ing the brachial plexus can also form more spherical than

tubular masses.

After finding branched tubular masses in a brachial

plexus of these patients they were more extensively imaged

Fig. 1. Transverse ultrasound image of normal canine axilla. Vessels arehypoechoic (A, axillary artery; V, axillary vein). The nerve is found runningbetween the vessels (N, nerve) and is not always easily visualized.

Fig. 2. Transverse image of a brachial plexus tumor. The hypoechoictumor travels between the axillary artery and vein (A, axillary artery; V,axillary vein; N, peripheral nerve sheath tumor). The normal architecture isslightly distorted (compare to Fig. 1).

Fig. 3. Transverse image of brachial plexus tumor, with color Doppler.The axillary artery (A) and vein (V) have flow and are separated by thetubular, hypoechoic brachial plexus mass (outlined by arrows). The mass canbe differentiated from the vasculature by its lack of flow.

Fig. 4. Longitudinal ultrasound image of canine axilla. The hypoechoicvessels travel together (A, axillary artery; V, axillary vein). The axillary arteryis smaller and has more conspicuous walls. The same vessels can enter andleave the scan plane.

515Brachial PlexusTumorUltrasound EvaluationVol. 46, No. 6

with either CT or MR imaging. Selection between these

modalities was determined by the primary clinician.

Results

A 10-year-old male Labrador retriever had right fore-

limb lameness, especially noticeable during exercise. Treat-

ment for arthritis did not result in improvement and

lameness progressed. There was extensive muscle atrophy

of the affected limb, a lack of conscious proprioception in

the right forelimb and right-sided Horner’s syndrome. Ul-

trasonographically there was a large, tubular mass in the

region of the brachial plexus. The mass appeared to extend

into the foramen at C6–C7 and traveled along neurovas-

cular plexus. The findings were consistent with a brachial

plexus tumor. MR imagingw of the axillary region was

performed and there was a mass in the brachial plexus. A

definitive histopathological diagnosis was not made but the

mass was presumed to be a brachial plexus tumor based on

the MR images.

A 10-year-old female Golden Retriever had a right tho-

racic limb lameness that progressed for 2 months. There

were decreased triceps and withdrawal reflexes on physical

examination. Ultrasonographically there was a mass in the

right axilla between the axillary artery and vein. The mass

was hypoechoic and tubular and lacked flow. The neuro-

logic signs and axillary mass were consistent with a bra-

chial plexus tumor. The presence of a brachial plexus

tumor was confirmed in MR images of the axilla. The lo-

cation of the mass between the axillary artery and vein was

consistent with a brachial plexus tumor. An aspirate of the

mass taken with a 22-gauge hypodermic needle was inter-

preted as a benign peripheral nerve sheath tumor.

An 8-year-old male Australian Shepherd referred to the

VMTH had unilateral left forelimb lameness and no his-

tory of trauma. There was a lack of conscious propriocept-

ion and a triceps reflex in the affected limb. A mass within

the brachial plexus was suspected but could not be defin-

itively diagnosed on the initial ultrasound scan. MR

imaging was performed and several contrast-enhancing

masses were found involving the brachial plexus. The pa-

tient was immediately re-scanned with ultrasound follow-

ing MR imaging and several hypoechoic, tortuous

structures were found within the axillary region. These

structures resembled blood vessels but lacked flow. Histo-

logically the multiple tumors were malignant peripheral

nerve sheath tumors. Gross examination found almost all

nerves of the brachial plexus and the spinal nerves were

partially or completely replaced by malignant peripheral

nerve sheath tumors.

An 11-year-old mixed breed female dog had pain and

lameness after jumping into a car. There was unilateral left

foreleg lameness with associated muscle atrophy. There

were no deficits in reflexes or conscious proprioception,

but there was cervical pain on palpation. Ultrasonograph-

ically there was a 5 cm mass in the region of the left thorax

extending from the body wall. The mass also extended

to the first rib and the brachial plexus region and encircled

a portion of the third rib. In CT imagesz significant

bony involvement of the tumor was seen. The definitive

diagnosis of rhabdomyosarcoma was determined from a

biopsy acquired with a 16ga. biopsy-T needley under

ultrasound guidance. Although this tumor was not a

peripheral nerve sheath tumor, its presentation and patho-

genesis were similar.

A 5-year-old male Labrador retriever had left thoracic

limb lameness. There was muscle atrophy of the affected

limb but no pain on palpation. The only abnormality on

the neurologic examination was decreased conscious prop-

rioception in the affected limb. Ultrasonographically there

was a tubular branching infiltrative mass following the ne-

urovascular bundle. In MR images the mass could be

traced proximally to the C8 nerve root, but did not involve

the intervertebral foramen. During left thoracic limb am-

putation the C8 nerve root was found to be severely en-

larged and tumor involvement of C6, C7, and T1 nerve

roots was also suspected. A left-sided C6–T1 hemilaminec-

tomy was performed and all nerve roots proximal to the

vertebral foramina were removed. The histopathologic di-

agnosis was a malignant peripheral nerve sheath tumor.

Fig. 5. Brachial plexus tumor, longitudinal view. In a longitudinal viewbrachial plexus tumors (outlined by arrows) are tubular, hypoechoic massesthat appear similar to the vasculature. They can be distinguished from vesselswith color Doppler, slowly rotating the probe on it axis.

wSigna LX, General Electric, Milwaukee,WI.zHigh Speed FXI scanner, General Electric, Milwaukee, WI.yTemno II scalpel tip biopsy needle, Adven Medical, Lubbock, TX.

516 Rose et al. 2005

Discussion

Ultrasound was effective in detecting brachial plexus

tumors in the axillary region. All 5 patients described in

this paper had a lameness and neurologic deficits in the

affected limb. Ultrasonographically all dogs had hypo-

echoic, tubular axillary masses with no blood flow. The

patients were subsequently evaluated using CT or MR im-

aging to support the ultrasound and physical examination

findings as well as fully examine the extent of the tumors to

determine if surgical resection was possible.

Due to their complexity, it was not always possible to

image the entire tumor with ultrasound. Difficulty in gain-

ing access with the transducer makes evaluation of regions

of the spine from C6–T2 to detect extension of the tumor

into the intervertebral foramina challenging with ultra-

sound. Cross-sectional measurements can be made but this

may have no correlation to the size or extent of the tumor.

The branching nature of peripheral nerve sheath tumors

may lead to a false estimation in the number of tumors.

More advanced imaging modalities (i.e., CT and MR im-

aging) are needed to fully examine the size, number, and

extension of the tumor(s). The depth of the tumors is also

variable with differences in musculature and adipose tissue.

The best approach to examining the brachial plexus was to

use landmarks in the axilla already mentioned.

Ultrasonography cannot replace CT or MR imaging to

fully delineate the extent of brachial plexus tumors, but it

be used as a screening tool. If a mass is identified, an in-

formed decision can then be made regarding management

of the disease which may include ultrasound guided biopsy

or further imaging to explore surgical options.

Though ultrasound was used successfully, there is po-

tential for false negative studies. Detection of a mass de-

pends on a variety of factors: size of the tumor, location of

the tumor, number of nerves affected and experience of the

operator. For these reasons, failure to detect a mass using

ultrasound does not eliminate the possibility of a brachial

plexus tumor and additional imaging is indicated if clinical

suspicion of a tumor remains.

There are a couple factors that could lead to a false

positive diagnosis. First, axillary lymph nodes in the area

of the brachial plexus could be identified as a tumor. These

lymph nodes will have an oblong rather than tubular shape

and will have a definitive border, unlike a peripheral nerve

sheath tumor, which usually branches and intersects with

normal nerve tissue. As mentioned previously, color flow

Doppler is useful for the axillary exam to differentiate a

normal vessel from a tubular mass, but there will be a lack

of flow signal in the vessel if the ultrasound beam is per-

pendicular to the vessel. This artifact can be negated by

scanning from multiple angles and comparing the vascular

anatomy to the opposite, presumably normal leg.

This study is a preliminary investigation into the use of

ultrasound to detect tumors involving the brachial plexus.

Although brachial plexus tumors were found, the sensitiv-

ity and specificity of ultrasonography must be determined

with further studies. Each of the tumors in this paper had

grown to a size sufficient to affect function of specific

nerves leading to neurologic signs.

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