[An Unruptured Extracranial Saccular Aneurysm, Arising from the Fenestrated Posterior Inferior Cerebellar Artery Originated from Extracranial Vertebral Artery: Case Report].

We present an extremely rare case of an extracranial saccular aneurysm arising from the proximal end of a distal fenestration in the posterior inferior cerebellar artery (PICA), with the PICA originating extra-cranially from the vertebral artery (VA). [Case] A 71-year-old woman with hypertension, was referred to our hospital for hearing disturbance. After the incidental discovery of an unruptured aneurysm on magnetic resonance imaging, an angiography showed the aneurysm arising from the proximal end of the right distal fenestrated PICA. Both the aneurysm and the origin of the PICA were extracranial. The patient was treated conservatively because of the size and shape of the aneurysm. [Conclusion] A literature review revealed nine reported cases of fenestrated PICAs, two of which were aneurysms with fenestrated PICAs. This present case repot is the first to describe an extracranial aneurysm in a fenestrated PICA of extracranial origin. Embryologically, PICA fenestrations may represent remnants of a plexiform arterial channel between the primitive VA and a vertebrobasilar anastomosis.