Introduction: Fenestrations of the posterior communicating artery (PCoA) are extremely rare. Fenestrations are a true developmental malformation and arise from the incomplete fusion of the primitive vessels present during embryonic development. Fenestration-associated aneurysms most commonly occur at the proximal bifurcation, secondary to a weakening of the medial or muscularis layer. More rarely, aneurysms have also been reported at the distal confluence of the two limbs of the fenestration. The combination of such a proximal defect with local hemodynamic forces places this region at risk for aneurysmal formation (4).

Methods: We describe a 52-year-old female who presented with a subarachnoid hemorrhage secondary to a ruptured saccular aneurysm at the proximal limb of a fenestrated right PCoA. A literature search was performed for PCoA fenestrations and associated proximal aneurysms. We then analyzed Padget's embryological sections during intracerebral vascular development to better understand the mechanism for such fenestration formation (2).

Results: Fenestrations of the PCoA are uncommon and have only been documented three other times in the literature (1,3,5). PCoA fenestrations are rare among the fenestrations of the anterior circulation, and of the three cases documented only two were associated with an aneurysm and none of them actually ruptured. In this particular case, it was the PCoA aneurysm that ruptured, and securing of the aneurysm was required.

Conclusions: The association between fenestrations and aneurysmal formation is not uncommon, but deciding whether such aneurysms are more prone to rupture than their counterparts lacking a fenestration remains controversial. By stage 4 (12-14mm embryo size) of Padget’s embryological study of the intracerebral vasculature, the anterior and posterior choroidal arteries, as well the basilar and vertebral arteries and associated branches are clearly delineated. It appears that it may be the persistence of the trigeminal artery in the form of a prominent caroticobasilar anastomosis that results in a small PCoA near the junction with the basilar artery that leads to such a fenestration.

Patient Care: Aggressive treatment of these vascular anomalies are as important as aneurysms without associated fenestrations because they can rupture and cause significant morbidity and mortality.

Learning Objectives: It is unknown whether the incidence of rupture is higher for aneurysms without associated fenestrations, but management of these vascular anomalies must be equally as aggressive.

References: 1. Baba S, Fukuda Y, Mizota S, Hayashi K, Suyama K, Nagata I: Fusiform Aneurysm Associated with Fenestration of the Posterior Communicating Artery. Neurol Med Chir (Tokyo) 50:568-570, 2010 2. Padget DH: The development of the cranial arteries in the human embryo. Contri Embryol 32: 205-262,1948 3. Tripathi M, Goel V, Padma MV, Jain S, Maheshwari MC, Gaikwad S et al: Fenestration of the posterior communicating artery. Neurol India 51:75-76, 2003 4. Vucetic RR: Segmental duplication of the fetal anterior cerebral artery. J Anat 192:431-434, 1998 5. Yasargil MG: Microneurosurgery I. Stuttgart, Georg Thieme Verlag, 1984, pp 60-66