Transpetrosal Approach for a Giant Thrombosed P2 Segment Posterior Cerebral Artery Aneurysm

Abstract

Objective: Posterior cerebral artery (PCA) aneurysms are extremely rare and can be difficult to treat. We report successful trapping and thrombectomy of a giant thrombosed P2 segment aneurysm via a transpetrosal approach.

Case presentation: A 62-year-old woman was admitted to our hospital with a progressive left hemiparesis. Magnetic resonance imaging (MRI) showed a 30 mm mass lesion in the right ambient cistern. On vertebral angiography, the right P2 trunk was deviated medially and inferiorly, and the right posterior temporal artery (PTA) was not visualized. We diagnosed a giant thrombosed aneurysm of the right PTA. Surgery was performed via a right posterior transpetrosal approach. The proximal P2 was identified above the oculomotor nerve in the ambient cistern, and a giant PTA aneurysm was found. After coagulating the distal PCA, a temporary clip was applied to the proximal P2, the aneurysm wall was incised, thrombus was removed, and a permanent titanium clip was applied to complete trapping. Postoperative MRI showed disappearance of the aneurysm. The patient's left hemiparesis was resolved 2 months after the operation, and she was discharged home.

Conclusion: Although trans-sylvian and subtemporal approaches are often performed for P2 aneurysms, they have difficulty identifying the distal PCA and may require excessive brain retraction. The transpetrosal approach can also be effective for giant thrombosed P2 aneurysms.

Keywords: giant thrombosed aneurysm; posterior cerebral artery; transpetrosal approach.

Fig. 1. (A) Axial T2-weighted magnetic resonance imaging (MRI) on admission demonstrates an extra-axial mass in the right ambient cistern causing marked compression of the right cerebral peduncle. Coronal (B) and sagittal (C) T1-weighted enhanced MRI shows homogeneous peripheral enhancement. Magnetic resonance angiography (D) demonstrates the lesion as an avascular area, and the right posterior cerebral artery is occluded distally. On anteroposterior (E) and lateral (F) left vertebral angiography, the right P2 is shifted medially and inferiorly, elongated, and tenuous; no contrast is visualized in the posterior temporal artery.

Fig. 2. Intraoperative photograph showing the view after a right posterior transpetrosal approach (asterisk: aneurysm; black arrow: oculomotor nerve; white arrow: P2 main trunk; white arrowhead: proximal posterior temporal artery (PTA); black arrowhead: distal PTA). (A) The right oculomotor nerve and proximal P2 can be seen in the ambient cistern; the giant aneurysm is located distally along the right posterior temporal artery. (B) The distal P2 is coagulated. (C) Intra-aneurysmal thrombus is excised after temporary clip placement. Postoperative contrast-enhanced axial T1-weighted magnetic resonance imaging demonstrates a shrunken residual aneurysm (D) without evidence of cerebral infarction on diffusion-weighted sequences (E).

Fig. 3. Schematic drawing of the surgical approach in the right side. (A) subtemporal approach; (B) posterior transpetrosal approach (black arrow: approach route; asterisk: aneurysm; white arrow: oculomotor nerve; black arrowhead: proximal PCA; white arrowhead: distal PCA). B: brainstem, C: cerebellum, PCA: posterior cerebral artery, T: temporal lobe.