= EXTRADURAL HEMATOMA

= hematoma within potential space between naked inner table of skull + calvarial periosteum (inner dura layer), which is bound down firmly to cranium at sutural margins (= subperiosteal hematoma of inner table)

Incidence: 2% of all serious head injuries; in <1% of all children with cranial trauma; uncommon in infants

Cause: impact on skull causes linear fracture + laceration of periosteal layer of outer table; temporary inward displacement of fragments lacerates meningeal vessels and strips both dural layers from inner table while the inner layer (meningeal dura) remains intact; blood accumulates between naked inner table and dura

Age: more common in younger patients 20–40 years ← dura more easily stripped away from skull

Associated with:

1. Skull fracture in 75–85–95%
   • best demonstrated on skull radiographs
   • Skull fractures frequently not visible in children (“ping-pong fracture”)!
2. Subdural hemorrhage
3. Contusion

Source of bleeding:

1. laceration of (middle) meningeal artery (high pressure) / meningeal vein (low pressure) adjacent to inner table from calvarial fracture (91%)
2. disruption of dural venous sinuses (transverse / superior sagittal sinus) with low pressure + high flow ← diastatic fracture of lambdoid / coronal suture (major cause in younger children)
3. avulsion of diploic veins / marrow sinusoids at points of calvarial perforations

Time of presentation: within first few days of injury (80%), 4–21 days (20%)

• transient loss of consciousness(= brief period of unconsciousness from concussion of brainstem)
• “lucid interval” (in <33%)
• delayed somnolence (24–96 hours after accident) due to accumulation of epidural hematoma:
  • DANGEROUS because of focal mass effect + rapid onset (NEUROSURGICAL EMERGENCY unless small)!
• progressive deterioration of consciousness → coma
• focal neurologic signs: 3^rd nerve palsy (as a sign of cerebral herniation), hemiparesis
  ◊ Only a minority of skull fractures across the middle meningeal artery groove result in an epidural hematoma!

Types:

1. acute epidural hematoma (58%) from arterial bleeding
2. subacute hematoma (31%)
3. chronic hematoma (11%) from venous bleeding

Factors determining the rate of epidural expansion:

• injury to artery or vein, spasm of artery, containment of bleed through pseudoaneurysm or tamponade, decompression of hematoma into meningeal + diploic veins or through fracture into scalp

Location:

• Most commonly clinically significant if located in temporoparietal region!
  1. in 66% temporoparietal (most often from laceration of middle meningeal artery)
  2. in 29% at frontal pole, parietooccipital region, between occipital lobes, posterior fossa (most often from laceration of dural sinuses by fracture)
• NO crossing of sutures unless diastatic fracture of suture present!

CT:

• fracture line in area of epidural hematoma
• expanding biconvex (lenticular = elliptical) extra-axial fluid collection (most frequent) = under high pressure:
  • usually does not cross suture lines
  • separation of venous sinuses / falx from inner table
    • The ONLY intracranial hemorrhage displacing falx / venous sinuses away from inner table!
• hematoma usually homogeneous:
  • fresh extravasated blood (30–50 HU) / coagulated blood (50–80 HU) in acute stage
  • rarely with hypoattenuated “swirl” ← admixture of fresh blood into clotted blood during active bleeding
• mass effect (“compression cone effect”) with effacement of gyri + sulci from:
  • epidural hematoma (57%)
  • hemorrhagic contusion (29%)
  • cerebral edematous swelling (14%)
• marked stretching of vessels
• signs of arterial injury (rare): contrast extravasation, arteriovenous fistula, middle meningeal artery occlusion, formation of pseudoaneurysm

MR:

• low intensity of fibrous dura mater allows differentiation of epidural from subdural blood in the late subacute phase (= extracellular methemoglobin) with hyperintensity on T1WI + T2WI

Angio:

• meningeal arteries displaced away from inner table of skull
• pseudoaneurysm = extravasation of contrast material
• arteriovenous fistula at fracture line

Cx: herniation, coma, death (15–30%)

Rx: after surgical evacuation return of ventricular system to midline

• Epidural hematoma at another site may be unmasked following surgical decompression!

DDx: Chronic subdural hematoma (may have similar biconvex shape, crosses suture lines, stops at falx, no associated skull fracture, no displaced dura on MR)