Extradural haematoma (EDH), also known as an epidural haematoma, is a collection of blood that forms between the inner surface of the skull and outer layer of the dura, which is called the endosteal layer. They are usually associated with a history of head trauma and frequently associated skull fracture. The source of bleeding is usually arterial, most commonly from a torn middle meningeal artery.

Extradural haematomas are typically biconvex in shape and can cause a mass effect with herniation. They are usually limited by cranial sutures, but not by venous sinuses. Both CT and MRI are suitable to evaluate extradural haematomas. When the blood clot is evacuated promptly (or sufficiently small to be treated conservatively), the prognosis of extradural haematomas is generally good.

Intracranial venous extradural haemorrhages and spinal epidural haemorrhages are discussed separately. 

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 who has sustained a head injury (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 (lucid interval), 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 burr holes.

See the article: extradural haemorrhage vs subdural haemorrhage.

Pathology

The source of bleeding is typically from a torn meningeal artery, usually the middle meningeal artery (75% ⁷). An associated skull fracture is present in ~75% of cases ³. Pain (often severe headache) is caused by the stripping of dura from the bone by the expanding haemorrhage. The posterior fossa is a rare location for traumatic injury, in general, including extradural haematomas ^3,4.

Occasionally, an extradural haematoma can form due to venous blood, typically a torn sinus with an associated fracture: see venous extradural haemorrhage.

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

It is important to realise that in the setting of sutural diastasis, extradural haematomas can cross sutures, as the continuation of the parietal (periosteal) component of the dura through the suture - which usually limits spread - is likely also to be disrupted. 

Location

Extradural haematomas are generally unilateral in more than 95% of cases, however, bilateral or multiple extradural haematomas are reported.

• >95% are supratentorial

  • temporoparietal: 60%

  • frontal: 20%

  • parieto-occipital: 20%

• <5% are located infratentorially in posterior fossa ⁴

Special locations to consider, particularly those related to venous extradural bleeding, include: 

• vertex extradural haematoma (which displaces the superior sagittal sinus) ⁶

• anterior middle cranial fossa (anterior temporal) ⁷

  • likely venous bleeding (from the sphenoparietal sinus)

  • do not cause midline shift or herniation

  • rarely enlarge

  • can often be managed conservatively 

Radiographic features

The morphology of extradural haematomas is best understood by reviewing their relationship to the bone and dura. An extradural haematoma is actually a subperiosteal haematoma located on the inside of the skull, between the inner table of the skull and parietal layer of the dura mater (which is the periosteum). As a result, extradural haematomas are usually limited in their extent by the cranial sutures, as the periosteum crosses through the suture continuous with the outer periosteal layer. This is therefore helpful in distinguishing extradural haematomas from subdural haematomas, which are not limited by sutures.

Extradural haemorrhages can, however, cross and elevate venous sinuses as long as there is no suture there; after all a venous sinus is located between the parietal and visceral layer of the dura.

Unfortunately, these rules are not foolproof and not infrequently extradural haematomas do cross sutures. One series found up to 11% of extradural haematomas in children cross sutures ⁵. This occurs in many scenarios: 

• skull fracture across the suture ⁵

• sutural diastasis ⁵

• vertex extradural haematomas, usually due to venous extradural haemorrhage, often cross the midline elevating the superior sagittal sinus ⁶

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.

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

MRI

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

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

Intravenous contrast may demonstrate displaced or occluded venous sinus in case of the venous origin of extradural haematomas.

Angiography

It can be used to evaluate nontraumatic cause (i.e. AVM) of extradural haematomas. Rarely angiography can demonstrate middle meningeal artery laceration and contrast extravasation from the 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 without mass effect or swirl sign can be treated conservatively ², sometimes resulting in calcification of the dura.

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

• pseudoaneurysm

• arteriovenous fistula

Differential diagnosis

With 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

  • maybe hyperdense

  • enhances with contrast

  • usually remote from the fracture (e.g. parafalcine)