PICA mirror aneurysms: Rarest of the rare

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, with an overview of the development of intracranial vessels and

possible embryological perturbations which may lead to formation of this exceedingly rare

anatomic abnormality.