Posterior inferior cerebellar artery aneurysms: Anatomical variations and surgical strategies

Abstract

Context:Posterior inferior cerebellar artery (PICA) aneurysms are associated with multiple anatomical variations of the parent vessel. Complexities in their surgical clipping relate to narrow corridors limited by brain-stem, petrous-occipital bones, and multiple neurovascular structures occupying the cerebellomedullary and cerebellopontine cisterns.Aims:The present study focuses on surgical considerations during clipping of saccular PICA aneurysms.Setting and Design:Tertiary care, retrospective study.Materials and Methods:In 20 patients with PICA aneurysms, CT angiogram/digital substraction angiogram was used to correlate the site and anatomical variations of aneurysms located on different segments of PICA with the approach selected, the difficulties encountered and the final outcome.Statistical Analysis:Comparison of means and percentages.Results:Aneurysms were located on PICA at: vertebral artery/basilar artery (VA/BA)-PICA (n=5); anterior medullary (n=4); lateral medullary (n=3); tonsillomedullary (n=4); and, telovelotonsillar (n=4) segments. The Hunt and Hess grade distribution was I in 15; II in 2; and, III in 3 patients (mean ictus-surgery interval: 23.5 days; range: 3-150 days). Eight patients had hydrocephalus. Anatomical variations included giant, thrombosed aneurysms; 2 PICA aneurysms proximal to an arteriovenous malformation; bilobed or multiple aneurysms; low PICA situated at the foramen magnum with a hypoplastic VA; and fenestrated PICA. The approaches included a retromastoid suboccipital craniectomy (n=9); midline suboccipital craniectomy (n=6); and far-lateral approach (n=5). At a follow-up (range 6 months-2.5 years), 13 patients had no deficits (modified Rankin score (mRS) 0); 2 were symptomatic with no significant disability (mRS1); 1 had mild disability (mRS2); 1 had moderately severe disability (mRS4); and 3 died (mRS6). Three mortalities were caused by vasospasm (2) and, rupture of unclipped second VA-BA junctional aneurysm (1).Conclusions:PICA aneurysms may present with only IVth ventricular blood without subarachnoid hemorrhage. PICA may have multiple anomalies and its aneurysms may be missed on CT angiograms. Surgical approach is influenced by VA-BA tortuosity and variations in anatomy, location of the VA-BA junction and the PICA aneurysm relative to the brain-stem, and the pattern of collateral supply. The special category of VA-PICA junctional aneurysms and its management; and, the multiple anatomical variations of PICA aneurysms, merit special surgical considerations and have been highlighted in this study.

Treatment strategies of ruptured posterior inferior cerebellar artery aneurysm according to its segment

“…[ 1 ] Fortunately, most LCNP resolve and the overall results are favorable in up to 76% of cases approximately 3 to 6 months after the procedure. [ 1 12 ] In our study, two of six patients (33.3%) that received microsurgical treatment at the proximal PICA aneurysm showed LCNP, and all patients progressed to develop permanent moderate neurologic deficits. However, there were no complications with unfavorable outcomes in the distal PICA aneurysm after microsurgical treatment.…”

“…And the incidence of LCNP while manipulating the PICA is high in patients with a proximal PICA aneurysm through lateral and far-lateral suboccipital approaches. [ 1 4 12 ] LCNP is also associated with the use of a temporary clip. [ 1 ] Incidence of LCNP after microsurgical clip is about 10–45%.…”

“…[ 4 ] The incidence of lower cranial nerve palsy (LCNP) while manipulating the PICA is high in patients with a proximal PICA aneurysm through lateral and far-lateral suboccipital approaches. [ 1 4 12 ] And the narrow and tortuous characteristics of the PICA during endovascular treatment (EVT) can cause vessel dissection, perforation, vasospasm, or aneurysmal rupture. Additionally, asymptomatic or symptomatic embolic infarct and unexpected parent artery occlusion can occur during EVT.…”

Distal posterior inferior cerebellar artery aneurysm with cerebellar arteriovenous malformation treated by open surgery: a case report

“…Surgical approaches for the PICA aneurysms can vary based on the aneurysmal location of the PICA segment, ruptured status, and necessity of posterior fossa decompression. The PICA is anatomically divided into five segments: anterior medullary, lateral medullary, tonsillomedullary, telovelotonsillar, and cortical branches [15]. An aneurysm located in the telovelotonsillar segment, like our case, is categorized as the distal aneurysm [16].…”

Application of Multimodal Neuromonitoring in Posterior Inferior Cerebellar Artery Aneurysm Clippings: Review of Two Cases

“…PICA aneurysms propose a higher risk of rupture than other aneurysms originating from the Circle of Willis with a mortality rate as high as 40% [3][4]. Due to their tortuous anatomic course and relationship with the brainstem, cerebellum, and cranial nerves, PICA aneurysms are technically difficult to access and postoperative neurological morbidity rates are high [4][5][6][7][8].…”