Mistaken identity: a case of false positive on CT angiography.

We describe the case of a 42-year-old female presenting with subarachnoid haemorrhage from a posterior inferior cerebellar artery (PICA) aneurysm rupture on intracranial digital subtraction angiography (DSA). One year postoperatively, the patient was followed with CT angiography and was reported to show a de novo aneurysm at the bifurcation of the left inferior cerebellar artery (ICA). Subsequent DSA revealed an aberrant vein crossing over the ICA bifurcation on mask phase images. This is the first reported case of a such a reason for a 'false positive' on CT angiography (CTA). The case demonstrates that although CTA has a reported high specificity, careful interpretation of multiple views is required to diagnose intracranial aneurysms when compared to the 'gold' standard of CTA. Copyright 2002 Elsevier Science Ltd.