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.

Epidemiology

Typically extradural hematomas 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 haemorrhage usually are precipitated by a clearly defined blow. A typical presentation is of a young patient involved in a head strike (either during sport or as part 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 (due to the stripping of the dura away from the bone). Over then next few hours they gradually loose 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 middle meningeal artery. An associated skull fracture is present in ~ 80% of cases. As the dura is stripped from the bone, pain is caused. In about 5 - 10% of patients the EDH is posterior fossa. Occasionally an EDH can form due to venous blood, typically a torn sinus with associated fracture.

Young patients being affected is not only a product of the prevalent demographics of patients with head injury, but also relates to the changes which occur in the dura in older patients. Anyone who has performed or assisted in crainotomies on older patients will know how much more tenaciously the dura adheres to the skull. 

Radiographic features

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. They are hyperdense, somewhat heterogenous, and sharply demarkated. 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 hyper dense, and a swirl sign may be evident ¹.

An extradural haematoma is essentially a sub-periosteal haematoma located on the inside of the scalp, between bone and outer layer of the dura (which is actually the periosteum). As a result it is limited by the 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.

Treatment and prognosis

Prognosis, even with a relatively large haemotoma, is in general quite good, as long as the clot is evacuated in time. 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:

• pseudoaneurysm
• arteriovenous fistula

Differential diagnosis

In large hematomas, 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. 

• 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 fracture (e.g. parafalcine)