The Effect of Epidural (Extradural) Hemorrhage

What is the typical cause of an extradural hematoma

Rupture of the middle mingeal artery, usually due to trauma at the pterion

Why can an extradural hematoma present w/ a lucid interval

Hematoma expands relatively slowly, and initial compensation occurs via CSF redistribution and venous blood displacement.
The skull is non-expansible, so compensatory mechanisms are quickly exhausted.

What are the early effects of rising intracranial pressure

Drowsiness progressing to coma

What type of herniation is classically caused by an extradural hematoma

Uncal herniation.

What happens to the pupil in CN III compression and why

Dilated and non-reactive due to loss of parasympathetic input to sphincter pupillae.

What eye position is seen in CN III palsy

Down and out due to unoppsoed action of lateral rectus and superior oblique. There is also pstosis due to paralysis of levator palpebrae superioris.

Why is the pterion clinically signifcant in extradural hematoma

It is thin and overlies the middle meningeal artery, making it prone to fracture and arterial rupture.

What is uncal herniation

Displacement of the medial temporal lobe (uncus) through the tentorial notch due to raised ICP.

What is the tentorial notch

An opening in the tentorium cerebelli that allows passage of the midbrain.

Why is CN III vulnerable during uncal herniation

It runs along the edge of the tentorium and is compressed against it.