The initial CT demonstrated deep midline edema; the differential is long but includes deep cerebral vein thrombus, artery of percheron infract and top of basilar syndrome.

MRI did not demonstrate any acute ischemia but did identify tortuous veins overlying the cerebellar hemisphere, suggesting venous hypertension as a cause for the edema. Venous occlusion and retrograde arterial flow into the venous system are two possible causes of venous hypertension.

A CT angiogram was arranged to assess patency of the deep cerebral veins but was inconclusive, DSA was then recommended.

High frame rate DSA demonstrated arterial shunting into the superior/inferior vermin veins and cerebellar cortical veins. The artery supplying the shunt was a vessel which normally supplies the posterior fossa dura, hence dural artery-venous fistula. The vermian veins and cerebellar cortical veins were tortuous and dilated. There was no shunting/arterial flow into the dural venous sinuses. The fistula was therefore graded as a Cognard type IV (direct drainage into cortical veins, venous ecstasies, high annual risk of intracranial hemorrhage).

The fistula was treated via a trans-arterial approach using a liquid embolic agent. On repeat angiography the fistula was completely occluded.