Diagnostic Imaging of Cerebral Trauma

C.N.S.Cerebral Trauma

Mohamed Zaitoun

Assistant Lecturer-Diagnostic Radiology Department , Zagazig University Hospitals

EgyptFINR (Fellowship of Interventional

Neuroradiology)[email protected]

Knowing as much as possible about your enemy precedes successful battle

and learning about the disease process precedes successful management

Cerebral Trauma(i) Primary Effects(ii) Secondary Effects(iii) Delayed Effects

(i) Primary Effects :a) Fractureb) Extra-Axial Hemorrhagec) Intra-Axial Injury

a) Fracture :1-Linear fractures (common)2-Complex fractures (diastatic, stellate &

depressed) tends to occur with mechanisms involving greater degrees of force

3-Skull base fractures may be occult (2ry clues are fluid in the sphenoid sinus or mastoid air cells and pneumocephalus)

4-Facial nerve palsy or ossicular disruption in temporal fractures

CT scan of 35-year-old male with recent motor vehicle accident demonstrating longitudinal fracture of the right petrous bone (thin arrow) that extends into the skull base (thick arrow)

Axial non-contrast CT scan at the time of initial injury showed a diastatic left parietal fracture and an underlying hemorrhagic brain contusion

b) Extra-Axial Hemorrhage :1-Epidural Hematoma2-Subdural Hematoma3-Subarachnoid Hemorrhage4-Intraventricular Hemorrhage5-Subdural Hygroma

1-Epidural Hematoma : (See Stroke)a) Etiologyb) Radiographic Features

a) Etiology :-Usually arterial bleed (middle meningeal artery)-95% are associated with fractures (classically

caused by fracture of the squamous portion of the temporal bone)

b) Radiographic Features :-95% are unilateral , temporoparietal-Biconvex , lenticular shape-Does not cross suture lines (as the dura is tightly

adherent to the cranium)-May cross dural reflections (falx tentorium) , in

contradistinction to subdural hematoma-Commonly associated with skull fractures-Heterogeneity predicts rapid expansion of EDH , with

areas of low density representing active bleeding-Staging of hematoma (See Intracerebral Hematoma)

Left parietal epidural hematoma, (A) T1, (B) T2, hematoma shows high signal on both images, which is consistent with extracellular methemoglobin

2-Subdural Hematoma : (See Stroke)a) Etiologyb) Radiographic Featuresc) Differential Diagnosis

a) Etiology :-Caused by traumatic tear of bridging veins

(rarely arteries)-In contradistinction to EDH , there is no

consistent relationship to the presence of skull fractures

-Common in infants (child abuse , 80% are bilateral or interhemispheric) and elderly patients (20% are bilateral)

b) Radiographic Features :-95 % supratentorial-Crescentic shape along brain surface-Crosses suture lines (since it is underneath the dura , the

hematoma can extend across the cranial sutures)-Does not cross dural reflections (falx , tentorium)-Staging of hematoma (See Intracerebral Hematoma)-An isodense subdural hematoma is isoattenuating to gray

matter , this occurs in the subacute phase (1-3 weeks after the initial injury) , 3 important clues alerting to the presence of an isodense subdural are :

1-Increased mass effect2-White matter buckling3-Apparently thickened cortex

CT of an 87-year-old female status post fall showing a large subdural hematoma along the left cerebral convexity with significant midline shift and effacement of the left lateral ventricle

CT of an 80-year-old female status post fall showing a large left subdural hematoma in addition to substantial subarachnoid hemorrhage (arrows)

c) Differential Diagnosis :

EDH SDH

1-Incidence <5 % of TBIs 10-20%

2-Cause Fracture Tear of cortical veins

3-Location Between skull & dura Between dura & arachnoid

4-Shape Biconvex Cresentic

5-CT 70 % hyperintense , 30 % isointense

Variable depending on age

6-T1 Isointense Variable depending on age

3-Subarachnoid Hemorrhage : (See Subarachnoid hemorrhage)

-Post traumatic SAH usually low volume scattered bleeds ; peripheral distribution

-Trauma is the most common cause of SAH while aneurysm rupture is the most common cause of non-traumatic SAH

Traumatic SAH , high density blood (arrowheads) fills the sulci over the right cerebral convexity in this subarachnoid hemorrhage

4-Intraventricular Hemorrhage :-Can occur due to tearing of subependymal

veins or from direct extension of subarachnoid or intraparenchymal hematoma

-Patients with intraventricular hemorrhage are at increased risk of developing noncommunicating hydrocephalus due to ependymal scarring which may obstruct the cerebral aqueduct

5-Subdural Hygroma :1-Etiology2-Radiographic Features

1-Etiology :-Accumulation of CSF in subdural space after

traumatic arachnoid tear

2-Radiographic Features :-CSF density-Does not extend into sulci-Vessels cross through lesion-Main considerations in differential diagnosis :1-Chronic SDH2-Focal atrophy with widened subarachnoid

space

c) Intra-Axial Injury :1-Coritcal Contusion2-Intraparenchymal Hematoma3-Diffuse Axonal Injury

1-Contusions :a) Etiologyb) Locationc) Radiographic Features

a) Etiology :-Focal hemorrhage / edema in gyri secondary to

traumatic contact of the cortical surface of the brain against the rough inner table of the skull

b) Location :-Characteristic locations are :1-Anterior temporal lobes , 50 %2-Inferior frontal lobes , 30 % (impact against

bony anterior walls of anterior & middle cranial fossae)

3-Parasagittal hemisphere4-Brainstem

c) Radiographic Features :-Initial CT is often normal , later on , low density lesions with

or without blood in them develop-Lesions evolve with time , delayed hemorrhage in 20%-Larger mixed attenuation (CT) or signal (MRI) intra-axial

lesions-A subacute cortical contusion may show ring enhancement

and should be considered in the differential of a ring enhancing lesion if there is a history of trauma

-Chronic contusion appears an encephalomalacia on CT , MRI is more specific showing peripheral hemosiderin deposition as hypointense on T2 and blooming artifact on gradient echo sequences

Hemorrhagic progression of a contusion (HPC), (A and B) A 21-year-old female pedestrian struck by a motor vehicle had a computed tomography (CT) examination performed within 2 h of trauma, and a repeat CT examination 6 h later, note the expansion of the right frontal contusion

Acute brain contusion, axial CT obtained in a patient immediately after a high-speed motor vehicle accident demonstrates a large, right frontal contusion with hemorrhage and surrounding edema, a smaller, subtle, right temporal cortical contusion (short arrow) is noted, as well as a small, left frontal subdural hematoma (long arrow)

Left frontal fracture with pneumocephalus, brain swelling, and small hemorrhagic contusions in the basal frontal cortex

Axial CT obtained immediately after blunt trauma to the left convexity of the skull resulted in severe swelling of the entire left cerebral hemisphere with loss of the gyral pattern secondary to edema, a small collection of subarachnoid blood is present (up arrow), the right hemisphere shows contrecoup gliding contusions (down arrows)

CT scan shows bifrontal contusions following severe head trauma (arrows)

Evolution of an acute brain contusion, (A) Axial CT obtained immediately following severe blunt trauma to the head shows a small, left frontal epidural hematoma (arrow), extensive subgaleal bicranial hematomas are seen, (B) Companion CT obtained 6 days after trauma shows the small, left frontal epidural hematoma (long arrow) and smaller areas of subgaleal bicranial hematomas, note that the previously isoattenuating contusion in the right posterior temporal area is now evident (short arrows in B)

Resolution of a brain contusion, (A) Axial CT scan obtained on day 1 after a high-speed motor vehicle accident shows subtle evidence of bifrontal hemorrhagic contusions (arrows), (B) Axial CT scan obtained on day 2 shows increased hemorrhage within the inferior frontal cortex bilaterally (arrows), (C) Axial CT scan obtained on day 14 shows resolution of the bright blood (upper arrows) and residual areas of dark edema in both frontal lobes and a subtle area throughout the right temporal lobe (lower arrows)

Subacute contusion , (a) CT, (b) CT+C

T2 FLAIR SWI

2-Intraparenchymal Hematoma :-Traumatic intraparenchymal hematoma can

occur in various locations ranging from cortical contusions to basal ganglia hemorrhage (due to shearing of lenticulostriate vessels)

-Similar to cortical contusion, a subacute intraparenchymal hematoma may show ring enhancement

MRI of 66-year-old male after a motor vehicle accident showing a large right frontal intraparenchymal hemorrhage on the FLAIR (left image) and T2 (right image) sequences, the FLARE images shows diffuse, heterogeneous increased signal intensity consistent with evolving blood products with surrounding edema in the frontal lobe

3-Diffuse Axonal Injury (Traumatic Axonal Injury T.A.I., Axonal Shear Injury) :

a) Etiologyb) Locationc) Gradingd) Radiographic Features

a) Etiology :-DAI is due to axonal disruption from shearing

forces of acceleration / deceleration-It is most commonly seen in severe head injury-Loss of consciousness occurs at time of injury-The term traumatic axonal injury (TAI) has

recently been introduced as this injury pattern is thought to be multifocal rather than diffuse

b) Location :1-Grey-white junction2-Corpus callosum3-Dorsolateral midbrain

c) Grading :-The higher the grade , the worse the prognosis :1-Grade I DAI :-Involves only the gray-white junctions2-Grade II DAI :-Involves the corpus callosum3-Grade III DAI (most severe) :-Involves the dorsolateral midbrain

d) Radiographic Features :1-CT :-Initial CT is often normal-Scattered low attenuation lesions at grey-white

junction (high attenuation if hemorrhagic)2-MRI :-Gradient echo T2 is the most sensitive sequence to

detect hemorrhagic shear injuries also (however not all DAI is hemorrhagic)

-FALIR is most sensitive for nonhemorrhagic DAI (multifocal T2 bright lesions)

-Diffusion sequence show restricted diffusion in acute DAI due to cytotoxic edema and cell swelling

DAI , axial GRE shows several foci of susceptibility effect along the left high convexity representing punctate hemorrhagic foci of DAI (arrows)

Diffuse axonal injury, axial susceptibility weighted images show multiple small hypointense foci of hemorrhage within the right temporal lobe and midbrain (A), splenium of the corpus callosum (B) and right parietal lobe (C), which are usually hardly visible on other MR sequences

Axonal Shear Injury

Axonal Shear Injury

(ii) Secondary Effects :1-Cerebral Herniation2-Diffuse Cerebral Edema3-Arterial Dissection

1-Cerebral Herniation :a) Definitionb) Typesc) Radiographic Features

a) Definition :-Mechanical displacement of brain secondary to

mass effect-Herniation may be due to a mass lesion (such as

neoplasm or hematoma) or may be due to edema secondary to a large stroke , because the volume of the posterior fossa is especially limited , cerebellar infarcts are prone to herniation

b) Types :1-Subfalcine herniation2-Descending Transtentorial (uncal) herniation3-Ascending Transtentorial herniation4-Tonsillar herniation

c) Radiographic Features :(i) Subfalcine Herniation :-The most common intracranial herniation

pattern , characterized by displacement of the brain under the free edge of the falx cerebri due to raised intracranial pressure

-Cingulate gyrus slips under free margin of falx cerebri

-Compression of ipsilateral ventricle-Entrapment and enlargement of contralateral

ventricle (may result from foramen of Monro obstruction)

-May result in ACA ischemia (by compression of the ACA against the falx)

(ii) Descending Transtentorial (uncal) Herniation:-Second most common-A hemispheric mass initially produces subfalcine

herniation , as the mass effect increases , the uncus of the temporal lobe is pushed medially , begins to encroach on the suprasellar cistern , hippocampus follows , hippocampus effaces the ipsilateral quadrigeminal cistern >> both the uncus & hippocampus herniate inferiorly through the tentorial incisura

-Enlargement of ipsilateral CPA cistern

-Duret hemorrhage (anterior midbrain) , due to shearing of perforating vessels due to downward force on the brainstem

-Compression of the contralateral cerebral peduncle against Kernohan's notch causes a hemiparesis ipsilateral to the herniated side

-PCA ischemia : occipital lobe , thalami , midbrain-The ipsilateral cranial nerve (occulomotor nerve) may

be compressed leading to pupillary dilatation & CN III palsy (eye is down & out)

(iii) Ascending Transtentorial herniation :-Is the superior transtentorial herniation of the

cerebellar vermis due to posterior fossa mass effect

-The main complication of upward transtentorial herniation is obstructive hydrocephalus from aqueductal compression

-Loss of quadrigeminal cistern

(iv) Tonsillar herniation :-Cerebellar tonsils pushed inferiorly through the

foramen magnum causes compression of the medulla

-Compression of medullary respiratory centers is often fatal

2-Diffuse Cerebral Edema :a) Etiologyb) Radiographic Features

a) Etiology :-Massive brain swelling and intracranial hypertension

secondary to dysfunction of cerebrovascular autoregulation and alterations of the blood brain barrier

-Underlying causes include ischemia and severe trauma-Ischemia may be primary (e.g. anoxic , drowning) or

secondary to other brain injuries (e.g. large SDH) and may be followed by infarction

-More common in children (Hypoxic Ischemic Injury)-High morbidity / mortality rates

b) Radiographic Features :-Findings develop 24 to 48 hours after injury-Effacement of sulci and basilar cisterns-Loss of perimesencephalic cisterns (hallmark)-Loss of GM / WM interface (cerebral edema)-White cerebellum sign : diffuse decrease in density

of the supratentorial brain parenchyma with relatively increased attenuation of the thalami , brainstem and cerebellum

White cerebellum sign

CT without contrast shows the reversal sign with diffuse and extensive hypodensity of the cerebral cortices and relative sparing of the bas al ganglia and cerebellum

3-Arterial Dissection :a) Etiologyb) Locationc) Radiographic Featuresd) Complications

a) Etiology :-Blood splits the media , creating a false lumen that

dissects the arterial wall-Causes :1-Spontaneous or with minimal trauma (strain , sports)2-Trauma3-Hypertension4-Vasculopathy (FMD , Marfan syndrome)5-Migraine headache6-Drug abuse

b) Location :-carotid artery (starts 2 cm distal to bulb and

spares bulb) > ICA (petrous canal) > vertebral artery > others

c) Radiographic Features :1-CTA is preferred first study of choice, see

intimal flap and caliber change2-MRI / MRA :-T1 bright hematoma in vessel wall (sequence:

T1 with fat saturation ), must be interpreted in conjunction with MRA

-MRA string sign

Curved reformatted image from contrast-enhanced CT angiography shows the cervical ICA, cervical ICA dissection affects the ICA distal to the carotid bulb (white arrowhead) and tends not to extend beyond its entry into the petrous bone (black arrowhead)

Axial fat-saturated T1 shows slightly hyperintense wall thickening of the left ICA (arrowheads), a finding consistent with an early subacute intramural hematoma (methemoglobin phase)

Subacute dissection of the left ICA in a 55-year-old man with transient ischemia, (a, b) Axial T1 obtained with fat saturation (a obtained at a higher level than b) show a narrowed eccentric flow void (arrowhead) surrounded by a crescent-shaped circumferential subacute intramural hematoma that expands the vessel diameter, the hematoma spirals around the vessel lumen, (c) 3D MIP image from contrast-enhanced MR angiography shows narrowing and smooth irregularities of the ICA lumen distal to the carotid bulb, note the kinking of the ICA above the dissection

Axial T1 fat-suppressed demonstrates a crescent sign (arrow) around the right ICA

Long-segment high-grade stenosis (string sign) identified on CTA, which appeared occluded on MR imaging/MRA, (A and B), Curved planar reformatted images of the left ICA demonstrate flamelike tapering of the proximal vessel with wall thickening and long-segment high-grade stenosis (arrow), (C), Axial plane from CTA shows the tiny residual lumen of the vessel (arrow), (D), Contrast-enhanced MRA acquired on the same day demonstrates apparent occlusion just distal to the carotid bifurcation (arrow)

Right vertebral artery dissection with a pseudoaneurysm seen on CTA, which is not visualized on MR imaging/MRA, (A), Curved planar reformatted image from CTA of the distal right vertebral artery demonstrates irregularity (arrow) as well as a small distal pseudoaneurysm, (B), axial CTA source image shows contrast within the true lumen and the pseudoaneurysm anteriorly (arrow), (C), Contrast-enhanced MRA demonstrates the irregularity associated with the dissection, but not the pseudoaneurysm, (D), 2D time-of-flight MRA depicts the narrowed true lumen but does not show the pseudoaneurysm, presumably due to saturation of slow-flowing blood

Dissection of the left cervical ICA in a 46-year-old woman, (a) Axial image from CT angiography shows enlargement of the overall vessel diameter (arrows) and a narrowed eccentric lumen (arrowhead), (b) Volume-rendered image from CT angiography shows a long tapered stenosis that begins distal to the carotid bulb (the string sign)

3-Conventional Angiography :-May establish the diagnosis and fully elucidate

abnormal flow patterns -Long segment fusiform narrowing of affected

artery

Angiographic images of the right ICA (A) and right VA (B), curved planar reformat images from the CTA study of the right ICA (C) and right VA (D), both demonstrate vessel wall irregularity, mild luminal narrowing, and pseudoaneurysm of the right ICA (arrows), (E), Corresponding MIP image from contrast-enhanced MRA shows both dissections (arrows), but with less clear depiction than that on CTA, (F), Axial T1 fat-suppressed demonstrates a crescent sign consistent with intramural hematoma around both the right ICA and VA (arrows)

d) Complications :1-Thrombosis2-Emboli and infarction3-Intramural hemorrhage4-False aneurysm

(iii) Delayed Effects :1-Atrophy2-CSF Leak3-AVF4-Pseudoaneurysm5-Leptomeningeal Cyst

1-Atrophy :a) Focal (following contusion)b) Generalized (following DAI or large extra-axial

hematomas which required surgical evacuation)

2-CSF Leak :-Secondary to fractures of frontal sinus , anterior

cranial fossa , sphenoid sinus , temporal bone (secondary meningitis)

(A,B), Left frontal lobe contusion with local atrophy, the first (A) and second (B) MR images were obtained 390 days apart

(C,D), Left parietal lesion and increased sulcal prominence, the first (C) and second (D) MR images were 118 days apart

3-Arteriovenous Fistula (AVF) :-Direct Caroticocavernous fistula (See Vascular

malformations)

4-Pseudoaneurysm :-Following arterial wall tear

CTA shows a 10 mm pseudoaneurysm in the right common carotid artery (black arrow)

Digital subtraction angiography of left internal carotid artery showing the pseudoaneurysm medial to ICA filling up with contrast with narrowed and irregular lumen of ICA (arrow)

5-Leptomeningeal Cyst :-Dura trapped within the fracture line-CSF pulsation prevents fracture healing leading

to growing fracture

Axial CT head shows expanded intradiploic space (CSF density) of the right temporal bone with resultant gross thinning of the tables

Axial non-contrast CT scan 7 weeks after trauma, showed an enlarging fracture with a cystic mass advancing through the bone defect, characteristic of a leptomeningeal cyst

CT shows growing skull fracture with underlying parenchymal injury with subdural collection and leptomeningeal cyst