Delayed Establishment of Collateral Circulation from Posterior Meningeal Artery After Proximal Occlusion of Posterior Inferior Cerebellar Artery: Case Report and Literature Review

BACKGROUND: A dissecting aneurysm on the posterior inferior cerebellar artery (PICA) is a rare entity, and endovascular embolization is often adopted. During the procedure, if the parent artery is occluded, the distal PICA is usually supplied by the ipsilateral anterior inferior artery or contralateral PICA. In extremely rare circumstances, the distal PICA can establish collateral circulation by transdural anastomosis with the posterior meningeal artery (PMA). CASE DESCRIPTION: A 29-year-old woman was admitted complaining of thunderclap headache, nausea, and vomiting for 3 hours. Head computed tomography and digital subtraction angiography revealed subarachnoid hemorrhage and a dissecting aneurysm located at the tonsillomedullary segment of PICA. The parent artery distal to the aneurysm had no collateral circulation from the adjacent arteries. Selective endovascular coiling of the aneurysm with preservation of the parent artery was adopted for treatment. The patient experienced an uneventful postprocedural recovery. To our surprise, follow-up digital subtraction angiography 6 months later revealed complete occlusion of the aneurysm and parent artery at the site of aneurysm formation. A rare anastomosis between the distal PICA and PMA was established. CONCLUSIONS: A report about this rare condition suggested that after occlusion of the PICA trunk, the distal PICA can form collateral circulation with the PMA. A potential collateral circulation may be present in advance between the PICA and PMA. When ischemia occurs in the distal PICA, this collateral circulation may open and could be reconstructed and enlarged to provide blood supply.