Nonsaccular aneurysms of the azygos anterior cerebral artery.
OBJECT
The azygos or undivided anterior cerebral artery (ACA) is a rare variant, and aneurysms associated with this variant are particularly rare. Most reported azygos ACA aneurysms are saccular, but the authors encountered four patients with this variant who had nonsaccular aneurysms. A review of the management of these lesions and this morphological distinction is presented.


METHODS
A retrospective review of patients with aneurysms treated over a 6-year period identified five Type I (according to the Baptista classification) azygos ACA lesions, of which four were nonsaccular. Aneurysms associated with other ACA variants (Baptista Types II and III) were excluded. Azygos ACA aneurysms accounted for 0.5% of all treated lesions and 1.7% of all ACA and anterior communicating artery aneurysms. One lesion in this series was located proximally at the azygos ACA origin, and three were located distally. All four aneurysms were large (>10 mm in diameter), and two were thrombotic. All aneurysms were treated with microsurgical clip occlusion.


CONCLUSIONS
Azygos ACA aneurysms are rare, and may have unusual nonsaccular anatomy (for example, fusiform shape, broad base, complex branching, and/or thrombus in the lumen). The nonsaccular morphology of these aneurysms may render them unsuitable for endovascular coil placement, and may complicate their microsurgical management.