imaging of head trauma part 2

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Imaging of Head Trauma Part 2: Pathology

Rathachai Kaewlai, MD

www.RadiologyInThai.com

Created: December 2006

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Checklist for Trauma Brain CT

Have 3 different windows to look for different pathology (brain, subdural and bone windows)

First image includes foramen magnum

Look first for the pathology that needs emergent Rx

Hydrocephalus

Look for primary pathology (hemorrhage in different compartments)

Look for secondary pathology (brain herniation, midline shift)

Look at the mastoid and sphenoid sinuses for hemorrhage which implies skull base fractures

Look at temporomandibular joints for fracture and/or dislocation (this pathology causes significant long term complications)

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Skull Fracture

Etiology-Pathogenesis Direct blow to the skull

Skull vault has 3 layers (outer table, diploe, and inner table) but diploe does not form where skull is covered by muscles (thin area, prone to fracture)

Areas prone to fracture: Squamous temporal/parietal bones (most common)

Foramen magnum, skull bases, cribiform plates, orbital roofs

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Skull Fracture

Epidemiology Fracture (fx) present in majority of severe head injury cases

Skull fx absent in 1/4 of fatal injuries at autopsy. Absence of skull fracture not excludes brain injury

1/3 of severely injured patients do not have skull fx

Concomitant cervical spine injury is 15% (cervical spine radiograph or CT may be needed)

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Skull Fracture

Fracture Suture

• Smooth or jagged edge • Serrated edge

• Straight line • Curvilinear

• Angular turn • Curvilinear

• Darker on X-ray • Lighter

• Greater in width • Lesser width

• Any locations • Specific anatomic location

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Skull Fracture

Imaging recommendation When suspects skull fracture

Head CT (in bone window, and edge enhancement algorithm*)

AND Scout CT (to look for fracture ‘in plane’ with axial scan)

Coronal and sagittal reformation is proven to be useful only when the scans were performed in helical mode (most hospitals scan the brain in conventional mode)

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* Consult your radiologist about the different CT algorithm. Edge enhancement algorithm is useful to detect bony lesions (in bone window).

Skull Fracture Linear, non-depressed

Run through the entire thickness of bone

Look if the fx line runs through a vascular channel, venous sinus. (This can cause epidural hematoma, venous sinus thrombosis and occlusion)

Almost always overlying soft tissue edema

Associated with extra-axial hematoma

Axial images of CT may miss fx that is ‘in plane’. Always check scout CT for obvious fx

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34-year-old man, fell from 10ft height

Retrospective review of the skull x-ray shows faint fracture line.

Axial CT: linear non-depressed fracture (red arrows) of left parietal bone. Note soft tissue hematoma overlying the fracture.

Skull Fracture - Depressed

Fragment (s) depressed inward

Consider open when Skin laceration over the fracture Through paranasal sinuses, middle ear structures

Potential surgical elevation in

Depressed > 5 mm and overlies motor or speech areas Depressed > skull thickness

Causes laceration of dura, arachnoid and possible brain parenchyma

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Middle age man, MVA, severe head injury

Axial CT (bone window) shows open depressed fractures (red arrows) of the right frontoparietal bone and presence of pneumocephalus (blue arrow). Severe soft tissue edema or hematoma.

3D CT, although not needed for diagnosis, helps radiologists and clinicians ‘see’ the complexity of fractures and plan for treatment.

Skull Fracture - Diastatic

Spreading of suture, 1-2 mm more than normal contralateral side

Coexisting linear fracture possible

May tear dural venous sinus, causing venous epidural hematoma (venous EDH), venous sinus thrombosis or occlusion

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Axial CT image shows diastasis fractures (red arrows) through left coronal suture and posterior portion of the sagittal suture. Normal suture is shown (blue arrow). Severe soft tissue swelling or hematomas overly the fractures.

35-year-old man, pedestrian hit by a car

Skull Fracture - Basilar

Clue: opacified sphenoid or mastoid

Problem associated:

Dural tear (patients come with CSF otorrhea or rhinorrhea)

Ear ossicles, labyrinth, cranial nerve (V, VI, VII) involvement Vascular injury- laceration, dissection, occlusion, infarction, carotid-cavernous

fistula

Presentations:

Temporal bone fx- CSF otorrhea, bruising over mastoid (Battle sign)

Anterior cranial fossa fx- CSF rhinorrhea, bruising around the eyes (raccoon eyes)

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Axial CT image shows the most common type of skull base fx; longitudinal fx (blue arrows) through the right temporal bone. Note disruption of the right ear ossicles (red arrow). Blood in bilateral sphenoid sinuses imply fractures through the sinuses. There is no fracture through the right carotid canal (C). If there is a suspicion of fracture through the carotid canal, CT angiography should be performed to rule out vascular injury.

Young man in high velocity MVA with bleeding from the right ear.

Skull Fracture - Pneumocephalus

Presence of air or gas in the cranial cavity

Principal cause = trauma

Indicates communication between intracranial and extracranial spaces, e.g. paranasal sinuses or ambient air

Significant complications: meningitis, CSF otorrhea or rhinorrhea

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Small pneumocephalus (red arrows) is seen in the subarachnoid space of the right frontal convexity. This patient had right frontal sinus fracture as a source of pneumocephalus. Presence of pneumocephalus should raise the suspicion of sinus fracture or open fracture to

the ambient air.

Epidural Hematoma (EDH)

Etiology-pathogenesis Source of bleeding most commonly middle meningeal artery

(85-90%) > others (dural sinus - venous EDH) Hematoma between inner table of the skull and dura

Underlying brain usually minimally injured. Good prognosis if treated aggressively

May cross midline and dural attachment Not cross sutures (exception: diastatic fx, large EDH)

Most common location = squamous part of temporal bone

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Epidemiology: Young men (20-40’s) - older people dura strongly adheres to

inner table of the skull Majority has skull fx

Clinical features:

Significant trauma

Loss of consciousness; Lucid interval found in 40% of patients

Delayed development 10-25%, within the first 36 hours

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CT findings Hyperdense biconvex extra-axial mass Low density area inside hematoma represents active bleeding (swirl

sign) Common to have herniation

Potential indications for surgery Size > 2 cm Active bleeding Pending herniation Corresponding neurological deficit

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Venous EDH Usually in posterior fossa

Depressed skull fx causes strip of the dura, giving potential space for blood accumulation

Tear of venous sinus (lhigh flow, low pressure)

More benign course, subacute presentation, usually not required surgery

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Young patient in MVA

Axial CT image shows a large lentiform-shaped homogeneous hyperdense mass in the right temporal convexity, consistent with epidural hematoma (red arrows). Nonvisualized temporal horn of the right lateral ventricle implies mass effect from the hematoma and degree of brain edema. Fracture is identified at the right squamous temporal bone (not shown).

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35-year-old man, fall from 12ft

Axial CT image shows a small lentiform-shaped homogeneous hyperdense mass in the left parieto-occipital convexity, consistent with epidural hematoma (red arrows). The proximity of the hematoma to the transverse sinus raises the possibility of dural venous sinus injury. Subsequent MRV and CTV show no evidence of venous sinus injury. The patient was discharged home.

Subdural Hematoma (SDH)

Etiology-pathogenesis: Blood collects between dura and arachnoid

Source of blood - torn cortical bridging veins, artery may also be torn

Epidemiology: Extremes of age - infant or elderly

Usually coexists with other brain injuries, i.e. subarachnoid hemorrhage

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Subdural Hematoma (SDH)

CT findings:

Acute SDH - crescent blood collection over hemisphere, displacing the cerebral cortex medially

Usually hyperdense (can be mixed due to unclottted blood or torn arachnoid)

Can be isodense if patients are anemic or blood mixes with CSF

Can cross suture

Can extend into interhemispheric fissure (thick falx), along tentorium

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35-year-old man, fall from height

Axial CT image shows a thin concave hematoma along the left temporal convexity, representing subdural hematoma (red arrows).

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Axial CT image (subdural window) shows thin bilateral hyperdense blood along the right parietal and left temporal convexities, representing acute subdural hematoma (red arrows). Small subarachnoid hemorrhage is also noted in the sulci of the right parietal lobe (blue arrow). Bilateral subdural hematoma can be subtle and easily missed on ‘brain window’.

Traumatic Subarachnoid Hemorrhage (tSAH)

Etiology-pathogenesis: Tear of veins in subarachnoid space

Epidemiology:

Most common cause of subarachnoid hemorrhage is trauma

tSAH usually associated with cerebral contusion, SDH, or other lesions. Nearly all cases of tSAH have other lesions to suggest traumatic cause

Isolated SAH in trauma patients; there is a possibility of ruptured aneurysm causing sudden loss of consciousness and then later trauma (ruptured aneurysm while driving, or having activities)

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Traumatic Subarachnoid Hemorrhage (tSAH)

CT findings: High density blood in sulci/cisterns

Location - next to contusion or under SDH/skull fx/scalp laceration (otherwise, look similar to aneurysmal SAH)

Traumatic intraventricular hemorrhage (tIVH) can coexist Seen as blood-CSF level in the ventricles

Subtle tSAH Blood in the interpeduncular fossa may be the manifestation of

subtle SAH

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58-year-old man, found down at home

Coronal reformatted CT image shows subarachnoid hemorrhage insinuated in the cerebral sulci of left parietal and right temporal lobes. Ruptured cerebral aneurysm is the main differential diagnosis in the patients presenting with pure subarachnoid hemorrhage with equivocal history of trauma.

Cerebral Contusion

Etiology-pathogenesis: Initial injury causes the contusion due to cerebral gyri impact

inner table of the skull (rough edges and ridges)

Evolve from petechial hemorrhage -> small hemorrhage -> large hematoma (imaging worsened with time)

More evident after 24h

Epidemiology: Most common parenchymal lesion in head trauma

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Cerebral Contusion

CT findings

Low density cortex (edema) mixed with high density blood (petechial hemorrhage)

Classic location: anterior base of frontal and temporal lobes

Multiple, bilateral

Can be normal early

Can be non-hemorrhagic

MRI is better for detection, delineating extents of contusions

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Axial CT image shows an ill-defined area of hypodensity and loss of grey-white matter differentiation in the tip of the left temporal lobe (red arrows); a typical location of this non-hemorrhagic contusion. Contusion without hematoma is difficult to appreciate on CT scan. MRI is more sensitive.

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Middle age man, fall from height

Hemorrhagic contusion (red arrows) at the frontal bases, right more than left, is noted as an ill-defined area of hypodensity in CT and high signal intensity zone in MRI T2-WI. MRI is more sensitive to depict the extent of this injury.

Diffuse Axonal Injury (DAI)

Frequent cause of persistent vegetative state and morbidity in traumatic brain injury patients

Etiology-pathogenesis

Traumatic deceleration injury: shearing/rotational forces in areas of greater density differential in the brain (= grey-white matter interface)

Can be an isolated finding in traumatic brain injury No (or little) association with presence of subarachnoid, subdural

hemorrhage, or skull fracture

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Clinical features Usually results in instantaneous loss of consciousness. Clinical

symptoms worse than CT findings Most patients (90%) remains in vegetative state (rarely causes

death because brainstem function typically unaffected)

General imaging features Can be either hemorrhagic or non-hemorrhagic (the latter is more

common) Grey-white matter interface, brain stem, corpus callosum Number and location of lesions predict prognosis (worst when

multiple, and in supratentorial location)

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CT findings May be normal (microscopic, nonhemorrhagic lesions can be

missed by CT)

Small hemorrhagic foci in typical locations

MR findings

MRI is the imaging of choice to detect DAI

Susceptibility sequence needed for detection of hemorrhagic DAI (called T2 GRE, or T2*). Hemorrhagic lesions will be dark.

Non-hemorrhagic lesions are bright on T2-WI and FLAIR

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Imaging recommendation for suspected DAI When initial brain CT is normal but the patient is in vegetative

state MRI with susceptibility sequence

OR

Follow up brain CT in 24 hours (1/6 of DAI will evolve, may be seen in subsequent CT)

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24-year-old woman, MVA, severe head injury, GCS 4T

Axial CT image shows mild diffuse brain swelling without intracranial hemorrhage. Small subgaleal hematoma is present (red arrow).

Same day MRI (Susceptibility sequence) shows multiple tiny areas of blood products (red arrows) in the grey-white matter junctions and deep grey nuclei consistent with DAI. Blue arrow represents a vascular flow void. Blue star is an artifact.

Vascular Effects of Trauma

Hemodynamic alterations common with traumatic brain injury

Spectrum of vascular abnormalities due to trauma Vasospasm, ischemia, infarction Pseudoaneurysm, arterio-venous fistula Laceration, dissection

Ischemia/infarction due to… Vasospasm Embolism from vascular injury Secondary to brain herniation

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Axial CT image done at day 2 after the injury shows a large right middle cerebral artery territory infarction (red arrows), in conjunction with acute subdural (blue star) and intraparenchymal hemorrhage in the right frontal base. The high density structure in the left parasagittal region is a part of an intracranial pressure monitoring device.

Cerebral Edema

Increased brain water (astroglial swelling)

Two types (vasogenic and cytotoxic edema) often coexists

In trauma: Vasogenic edema occurs immediately then cytotoxic edema

within hours

Usually adjacent or mixed with brain contusion

Generally resolves within 2 weeks

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23-year-old woman, MVA

Axial CT image shows edematous brain with loss of grey/white matter interface (red stars), compressed ventricle (arrow) and effacement of the sulci (not seeing any cerebral sulci) in this patient who had DAI confirmed by MRI.

Herniations

Usually more deteriorating than primary injury

Etiology-pathogenesis Hemorrhage accumulates within closed space, CSF spaces

compressed then mechanical displacement of brain occurs

May cause secondary ischemia or infarction

If not correct, brain death

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Axial CT image shows a midline shift to the left due to large right extra-axial hemorrhage (red stars) and intraparenchymal hemorrhage. The degree of midline shift (red line) is usually measured at the level of maximal deviation of the midline structure (septum pellucidum is a useful anatomy).

Subfalcine herniation is defined as herniation of cingular gyrus (blue star) underneath the falx cerebri. Presence of midline shift usually signify subfalcine herniation, and vice versa. ACA occlusion may become occluded.

Midline Shift & Subfalcine Herniation

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Obstructive Hydrocephalus & Descending (central) transtentorial herniation

Hydrocephalus is one of the most emergent finding to look for, because it is treatable. This patient had dilated left lateral ventricle from asymmetric brain edema (right more than left). Central herniation is defined as both temporal lobes descend through the tentorial incisura, which can be seen as effacement of the cistern around the midbrain (star).

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Make sure the lowest cut of CT image includes foramen magnum! Presence of space-occupying lesion in the brain, cerebellar tonsils (red stars) in the same cut as foramen magnum, obliteration of CSF space and displaced portions of cervicomedullary junction (M) are signs of tonsillar herniation. Tonsils can be low lying as a normal variation or a Chiari malformation.

Tonsillar Herniation

Brain Death

Etiology-pathogenesis: Severe increased ICP decreases cerebral blood flow, then

irreversible loss of brain function

Clinical criteria: coma + absent brainstem reflexes + apnea test

Imaging may confirm but does not substitute for clinical criteria

CT findings: No flow in intracranial arteries/venous sinuses Diffuse cerebral edema Hyperdense cerebellum (much denser than cerebrum)

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Contrast-enhanced axial CT (Left) shows diffuse SAH (blue stars) in the cerebral cisterns, diffuse cerebral edema. There is no intracranial blood flow either in arteries or venous sinuses. Both images show normal enhancement of extracranial vessels (red arrows). The patient had bilateral ventricular shunt placement.

49-year-old woman, ruptured cerebral aneurysm

The information provided in this presentation… Is intended to be used as educational purposes only.

Is designed to assist emergency practitioners in providing appropriate radiologic care for patients.

Is flexible and not intended, nor should they be used to establish a legal standard of care.

Thanks, MGH Radiology, for cases I’ve seen and things I’ve learned.

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