Straight sinus stenosis as a proposed cause of perimesencephalic non-aneurysmal haemorrhage.

Perimesencephalic nonaneurysmal haemorrhage (PMNH), a term first coined in 1985, is a diagnosis of exclusion. It is considered a benign form of subarachnoid haemorrhage with a good prognosis and a low risk of rebleeding. Its precise aetiology has not yet been determined.