Cerebral arteriovenous malformations (CAVM's) are a common form of cerebral vascular malformation and are composed of a nidus of vessels through which arteriovenous shunting occurs. They tend to be solitary in the vast majority of cases (>95%). The origin of arteriovenous malformations remains uncertain, although they are thought to be congenital.

The Spetzler-Martin AVM grading system allocates points for various features of intracranial AVM's to give a score between 1 and 5.  This case represents the extreme end of the scale - a grade 5 AVM.

Catheter angiography was performed following this acute bleed - the nature of the AVM on MRI was confirmed:

1. huge left parieto-occipital AVM
2. smaller right cortical parietal vascular lesion – this appears separate adjacent to the VP shunt entry point. This subsequently bled.
3. distended cortical veins and periventricular appearances are suggestive of cerebral venous hypertension, and perhaps responsible for the patient's decline prior to the cortical hemorrhage.