Posterior communicating artery aneurysm presenting withhaemorrhage into an arachnoid cyst

A patient is reported on with a subarachnoid haemorrhage(SAH) from an aneurysm of the posterior communicating artery, who initially presented with a sentinel bleed into an arachnoid cyst andnormal magnetic resonance angiography (MRA) of the intracranial vasculature which led to a delay in diagnosis. Although this is a veryrare presentation of a relatively common condition, it is important torecognise the importance of intracystic haemorrhage in suchcircumstances as well as the limitations of MRA, as a delay indiagnosis may have serious clinical consequences.