Clinical and Anatomical Characteristics of Perforator Aneurysms of the Posterior Cerebral Artery: A Single-Center Experience

Abstract

Introduction: Posterior cerebral artery (PCA) aneurysms represent up to 1% of all cerebral aneurysms. P1-P2 perforator aneurysms are thought to be even less prevalent and often require complex treatment strategies due to their anatomical and morphological characteristics, with risk of a perforator infarct. We studied the treatment of P1-P2 perforator aneurysms in a single-center cohort from a high-volume tertiary center, reporting clinical and anatomical characteristics, treatment strategies, and outcomes.

Methods: A retrospective analysis of adult patients with a P1-P2 perforator aneurysm who presented at our institution between January 2000 and January 2023 was performed. The patients were analyzed for demographics, clinical presentation, imaging findings, treatment techniques, outcomes, and complications. Subgroup analyses between ruptured versus non-ruptured cases were included.

Results: Out of 2733 patients with a cerebral aneurysm, 14 patients (0.5%) presented with a P1-P2 perforator aneurysm. All six patients with a ruptured aneurysm were treated by endovascular coiling, of whom one patient (16.7%) required surgical clipping of a recurrence. One out of eight (12.5%) patients with unruptured aneurysms was treated by surgical clipping. P1-P2 perforator aneurysms predominantly affected middle-aged individuals (median 59.5 years), with 10/14 (71.4%) being female. Endovascular coiling was the primary treatment modality overall, yielding favorable technical outcomes, however, it was complicated by a perforator infarct in two patients (33.3%) without new permanent morbidity or mortality secondary to treatment.

Conclusions: P1-P2 perforator aneurysms are a rare subtype of intracranial aneurysm. Endovascular coiling could present an effective treatment modality; however, care should be taken for ischemic complications in the dependent perforator territory. Larger studies are required to provide more insights.

Keywords: cerebral aneurysm; endovascular coiling; perforator artery; posterior cerebral artery.

Figure 1

Axial schematic illustrations of the segments of PCA perforators at the level of the midbrain and optic chiasm (A–C) representing the 3 major thalamoperforating groups, i.e., Pcom, P1, and P2, supplying different thalamic territories. The tuberothalamic arteries originate from the middle third of the PcomA (A), supplying the ventral thalamus. The paramedian P1 perforators originate from the P1 or precommunicating segment (B) and supply the medial thalamus and/or rostral midbrain. The inferolateral perforators, also known as geniculate perforators or direct perforators, originate from the P2 or postcommunicating segment (C) and can be divided into the P2A and P2B segments, or crural cistern and ambient cistern segments. The P2A segment supplies the lateral thalamus, whereas the P2B classically supplies the inferolateral pulvinar. An anatomical variant and replacement of the paramedian P1 perforators is the artery of Percheron, representing a single dominant trunk with bilateral supply to the thalamus and/or midbrain ((E,F); green dotted lines) and originating of the P1 segment. An anatomical variant replacing the inferolateral P2 perforators is the collicular artery (also known as the quadrigeminal or circumcollicular artery), coursing medially to the main P2 segment around the cerebral peduncle towards the collicular plate ((D–F); red dotted lines) and originating from the P1 or P2A segment. Its name is derived from the area of supply. An identical origin of the collicular artery and the artery of Percheron is possible (E,F), in which the nomenclature is defined by the territory of supply. The example case demonstrates the presence of a right P1 perforator aneurysm at the origin of the collicular artery and the artery of Percheron.

Figure 2

Case no 13 involves a 64-year-old female patient with a subarachnoid hemorrhage (GCS 15, WFNS 1) with the epicenter in the right interpeduncular cistern (A), with suspicion of a small superiorly and posteriorly pointing right P1 aneurysm ((B,C); yellow arrow). AP (D) and lateral left vertebral artery injections (E,F) confirm a right P1 aneurysm, with stases of contrast in the dome in the late arterial phase ((F); black arrow). Axial Xpert CT angiography reconstructions demonstrate the course of the right collicular artery in the crural and ambient cisterns along the posterior cerebral artery ((G–I); yellow arrows) originating medially from the dome of the aneurysm ((I); yellow arrow). An unassisted coiling with balloon presence was performed with two coils (J) resulting in direct (K) and one-year follow-up closure of the aneurysm on MRA time-of-flight (L). There is subtle indentation of the coil mass in the parent artery ((L); white arrow).