PICA mirror aneurysms: Rarest of the rare

Abstract

Mirror aneurysms, a subset of bilateral, symmetrically situated aneurysms occurring in corresponding intracranial vessels, are an intriguing radiological finding. They probably represent phylogenetic aberrations in the embryonic development of intracranial vasculature. The posterior circulation, particularly the posterior inferior cerebellar artery (PICA), is an infrequent site for mirror aneurysms, with only four cases being reported so far. Here we describe the fifth such case of an incidentally detected PICA aneurysm on digital subtraction angiography (DSA), with an overview of the development of intracranial vessels and possible embryological perturbations which may lead to formation of an exceedingly rare anatomic abnormality.