Coloured magnetic resonance imaging (MRI) axial section of the brain of a 30-year-old male patient with suspected subarachnoid hemorrhage (SAH). SAH is a rare, life-threatening type of stroke caused by bleeding into the space surrounding the brain (subarachnoid space). The scan shows the presence of a significant left fronto-parietal arteriovenous malformation (AVM, purple) with a nidus (abnormal tangle of blood vessels) fed by complex venous drainage.