Bilateral mirror posterior inferior cerebellar artery aneurysms: diagnostic caveat on catheter angiography.

Only three definitive cases of bilateral mirror proximal posterior inferior cerebellar artery (PICA) aneurysms have ever been reported. A fourth example is presented where each PICA aneurysm remained angiographically occult on contralateral vertebral artery angiography despite retrograde filling of the parent vessel PICA. Implications for clinical practice are discussed.