Subtonsillar Approach to a Polylobulated Posterior Inferior Cerebellar Artery Aneurysm: A Case Illustration

Dysplastic and polylobulated aneurysms of the posterior inferior cerebellar artery (PICA) present significant technical challenges because of their irregular geometry and proximity to the lower cranial nerves and brainstem perforators. When endovascular options carry elevated risks, microsurgical clip reconstruction remains a definitive treatment to restore the vascular architecture.

A 46-year-old woman presented for the elective surgical management of an unruptured, polylobulated left PICA aneurysm. She had a history of subarachnoid hemorrhage secondary to a ruptured anterior communicating artery aneurysm, which was successfully clipped alongside an unruptured right middle cerebral artery aneurysm in November 2024. Interdisciplinary case discussion considered endovascular treatment, including flow-diverting stents; however, the patient was unwilling to take dual antiplatelet therapy (aspirin and clopidogrel), and digital subtraction angiography demonstrated complex polylobulated morphology with multiple small perforators arising from the aneurysm base, making endovascular therapy high-risk. Microsurgical intervention was chosen because the surgical approach allowed for direct visualization and safe control of the aneurysm and surrounding neurovascular structures. A left medial suboccipital craniotomy with a subtonsillar approach was used. Stepwise reconstruction was performed using 2 straight mini clips (Aesculap No. 710 and 720) under continuous intraoperative neuromonitoring, including somatosensory evoked potentials, motor evoked potentials, and cranial nerve IX-XII electromyography. Multimodal verification, including microvascular Doppler, aneurysm puncture, and indocyanine green videoangiography, confirmed complete aneurysm obliteration and preservation of the parent vessel and perforators. The patient was discharged on postoperative day 4 without neurological deficits. Follow-up at 3 months confirmed favorable clinical and radiological outcome.

For complex PICA aneurysms, a systematic approach incorporating subtonsillar exposure and multimodal intraoperative verification helps ensure complete exclusion while protecting the local neurovascular circulation.