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Extradural haemorrhage

An extradural haematoma (EDH), also known as an epidural haematoma, is a collection of blood which forms between the inner surface of the skull and outer layer of dura. They are commonly associated with a history of trauma and associated skull fracture. The source of bleeding is usually a torn meningeal artery (most commonly, the middle meningeal artery). EDHs are typically biconvex in shape and can cause mass effect with herniation. They are limited by cranial sutures, but generally not by venous sinuses. Both CT and MRI are suitable to evaluate EDHs. When the blood clot is evacuated promptly (or treated conservatively when small), the prognosis of EDHs is generally good.

Epidemiology

Typically extradural haematomas are seen in young patients who have sustained head trauma, usually with an associated skull fracture.

Clinical presentation

Unlike subdural haemorrhages, in which a history of head trauma is often difficult to clearly identify, extradural haemorrhages usually are precipitated by clearly defined head trauma.

A typical presentation is of a young patient involved in a head strike (either during sport or a result of a motor vehicle accident) who may or may not lose consciousness transiently. Following the injury they regain a normal level of consciousness, but usually have an ongoing and often severe headache. Over the next few hours they gradually lose consciousness.

Due to the long cisternal course of the sixth cranial nerve (abducens nerve (CN VI)), it is often involved as downward herniation begins, usually on the side of the haemorrhage and can, in an emergency, guide exploratory burrholes.

Pathophysiology

The source of bleeding is typically from a torn meningeal artery, usually the middle meningeal artery. An associated skull fracture is present in ~80% of cases ref needed. Pain (usually severe headache) is caused by the stripping of dura from the bone by the expanding haemorrhage. In about 5-10% of patients, the EDH is in the posterior fossa ref needed. Occasionally, an EDH can form due to venous blood, typically a torn sinus with an associated fracture.

Young patients being affected is not only a result of the prevalent demographics of patients with head injury but also relates to the changes which occur in the dura in older patients, as the dura is much adherent to the skull.

Location

EDHs are usually unilateral in more than 95% of cases, however bilateral or multiple EDHs are reported.

  • 90-95% are supratentorial
    • temporoparietal: 60%
    • frontal: 20%
    • parieto-occipital: 20%
  • 5-10% are located infratentorially in posterior fossa

Radiographic features

CT

In almost all cases, extradural haematomas are seen on CT scans of the brain. They are typically bi-convex (or lentiform) in shape, and most frequently beneath the squamous part of the temporal bone. EDHs are hyperdense, somewhat heterogeneous, and sharply demarcated. Depending on their size, secondary features of mass effect (e.g. midline shift, subfalcine herniation, uncal herniation) may be present.

When acute bleeding is occurring at the time of CT scanning the non-clotted fresh blood is typically less hyperdense, and a swirl sign may be evident 1.

An extradural haematoma is essentially a subperiosteal haematoma located on the inside of the scalp, between bone and parietal layer of the dura mater (which is also the periosteum). As a result it is limited by the cranial sutures, which is helpful in distinguishing these from subdural haematomas (see below). Extradural haemorrhages can, however, cross and elevate venous sinuses as long as there is no suture there. It is only possible for extradural haematomas to cross sutures if there is a fracture with diastasis of an adjacent suture, in which case the dura is ruptured.

Postcontrast extravasation may be seen rarely in case of acute EDH and peripheral enhancement due to granulation and neovascularisation can be seen in chronic EDH.

MRI

MRI can clearly demonstrate the displaced dura which appears as a hypointense line on T1 and T2 sequences which is helpful in distinguishing it from subdural haematoma.

Acute EDH appears isointense on T1 and shows variable intensities from hypo- to hyperintense on a T2 sequence. Early subacute EDH appears hypointense on T2 while late subacute and chronic EDH are hyperintense on both T1 and T2 sequences.

Intravenous contrast may demonstrate displaced or occluded venous sinus in case of venous origin of EDH.

Angiography

It can be used to evaluate nontraumatic cause (i.e. AVM) of EDH. Rarely angiography can demonstrate middle meningeal artery laceration and contrast extravasation from middle meningeal artery into paired middle meningeal veins known as "tram track sign".

Treatment and prognosis

Prognosis, even with a relatively large haematoma, is in general quite good, as long as the clot is evacuated promptly. A smaller haematoma can be treated conservatively 2, sometimes resulting in calcification of the dura.

Occasionally delayed complications are encountered, usually relating to the injured meningeal vessel. They include:

Differential diagnosis

In large haematomas, there is rarely significant confusion as to the correct diagnosis. In smaller lesions, especially when there is associated parenchymal injury (e.g. cerebral contusions, traumatic subarachnoid blood, concurrent subdural haematoma) the diagnosis can be more challenging.

Differential considerations include:

  • subdural haemorrhage (SDH)
    • can cross sutures
    • usually sickle shaped
    • limited by dural reflections
    • usually in older patients or in young patients with significant other closed head injuries
  • meningioma
    • may be hyperdense
    • enhances with contrast
    • usually remote from fracture (e.g. parafalcine)

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