Aneurysm of the azygos pericallosal artery: diagnosis by MR imaging and MR angiography.

The azygos pericallosal artery represents a rare anatomic variant where only a single enlarged pericallosal artery is present instead of the usual two. The azygos pericallosal artery divides in the region of the genu of the corpus callosum, sending out branches to supply the mesial surfaces of both cerebral hemispheres. Although rare, with a reported incidence of between 0.2% and 4% (13), its greatest significance rests in the high frequency of berry aneurysms noted to occur at its bifurcation.