True Posterior Communicating Artery Aneurysms with High Risk of Rupture despite Very Small Diameter

Objective: This retrospective study investigated the clinical and angiographic characteristics of ruptured true posterior communicating artery (PCoA) aneurysms in comparison with junctional PCoA aneurysms presenting with a subarachnoid hemorrhage. Methods: The medical records and radiological data of 93 consecutive patients who underwent three-dimensional rotational angiography and surgical or endovascular treatment for a ruptured junctional or true PCoA aneurysm over an 8-year period were examined. Results: The maximum diameter of the ruptured true PCoA aneurysm (n=13, 14.0%) was significantly smaller than that of the ruptured junctional PCoA aneurysms (n=80, 4.45±1.44 vs. 7.68±3.36 mm, p=0.001). In particular, the incidence of very small aneurysms <4 mm was 46.2% (six of 13 patients) in the ruptured true PCoA aneurysm group, yet only 2.5% (two of 80 patients) in the ruptured junctional PCoA aneurysm group. Meanwhile, the diameter of the PCoA was significantly larger in the true PCoA aneurysm group than that in the junctional PCoA aneurysm group (1.90±0.57 vs. 1.15±0.49 mm, p<0.001). In addition, the ipsilateral PCoA/P1 ratio was significantly larger in the true PCoA aneurysm group than that in the group of a junctional PCoA aneurysm (mean PCoA/P1 ratio±standard deviation, 2.67±1.22 vs. 1.14±0.88; p<0.001). No between-group difference was identified for the modified Fisher grade, clinical grade at admission, and 3-month modified Rankin Scale score. Conclusion: A true PCoA aneurysm was found to be associated with a larger PCoA and ruptured at a smaller diameter than a junctional PCoA aneurysm. In particular, the incidence of a ruptured aneurysm with a very small diameter <4 mm was significantly higher among the patients with a true PCoA aneurysm.