Pterion fracture and extradural haematoma from middle meningeal artery tear
At the pterion, a thin junction of four skull bones, a fracture can tear the middle meningeal artery and let blood collect outside the dura, the skull's tough lining.
Remember
Thin bone at the pterion lies over the middle meningeal artery, so a side blow that fractures it can tear the vessel and cause an extradural haematoma. A lucid interval (a spell of looking well) before deterioration is a classic clue, but not every case has one.
Memory aid
thin bone, close artery, blood outside the dura
Use it to recall why a blow to the side of the skull can cause an extradural haematoma.
The pterion is a thin spot on the side of the skull, the junction of four skull bones: the frontal, parietal, temporal and sphenoid bones. Closely beneath it lies the middle meningeal artery, a main artery of the dura mater (the tough membrane that lines the inside of the skull).
When the side of the head takes a blow, the pterion can fracture and tear the artery beneath it. Arterial blood then collects between the skull and the dura, which is an extradural haematoma (extradural means outside the dura, and the bleed is also called epidural).
A brief loss of consciousness can be followed by a lucid interval: a spell when the person has apparently recovered and looks well while the clot is still small. With the clot growing in a rigid skull, the rising pressure compresses the brain, and worsening headache, drowsiness and falling consciousness follow.
The lucid interval is a classic clue, but not every extradural haematoma has one, so its absence does not rule the diagnosis out. Basal skull fractures (breaks in the floor of the skull) have other signs instead, such as blood in the middle ear, bruising around the eyes or clear fluid leaking from the nose.
Key facts
- Site
- the pterion is a thin spot on the side of the skull, the junction of four skull bones: frontal, parietal, temporal and sphenoid.
- Vessel
- the middle meningeal artery lies closely beneath the pterion, so a fracture there can tear it.
- Space
- the torn artery bleeds into the space between skull and dura, so the haematoma is extradural.
- Clue
- a brief loss of consciousness, then a lucid interval, then worsening headache, drowsiness and falling consciousness, though the lucid interval is not found in every extradural haematoma.
- Pressure
- the skull is a rigid box, so a growing clot raises the pressure inside and squeezes the brain.
- Contrast
- a basal skull fracture, a break in the floor of the skull, can give other signs, such as clear fluid leaking from the nose, blood in the middle ear or raccoon eyes (bruising around the eyes).
Exam traps
- A depressed fracture, where bone fragments are pushed inwards, is more likely to damage the brain directly, so it fits a visible dent and brain injury from the moment of impact. It does not identify the thin site over an artery that explains an apparent recovery followed by deterioration hours later.
- A fracture through the cribriform plate at the front of the skull floor can allow cerebrospinal fluid, the clear fluid around the brain, to leak into the nose. That signals a basal skull fracture, meaning a break at the skull base, and says nothing about a growing arterial bleed after a side blow.
- The superficial temporal artery on the side of the head lies outside the skull, so injuring it causes scalp bleeding, not a collection within the skull that raises the pressure. The artery inside the skull beneath the pterion is the middle meningeal artery.
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