Background: Extra-cranial posterior inferior cerebellar artery (PICA) aneurysms are rare with only 22 cases been reported so far. Intra-dural type of extra-cranial PICA aneurysm is even rarer with few case reports available. We report a previously unreported type of proximal PICA aneurysm in which the PICA aneurysm had intra-dural location at the C2 vertebral level.
Case description: A 51 year old gentleman presented with sub-arachnoid haemorrhage and intra-ventricular haemorrhage, predominantly involving the fourth ventricle and had no focal neurological deficit. CT angiogram was negative however a dedicated four vessel angiogram demonstrated an abnormal extracranial origin of right PICA at C1-C2 level, with associated aneurysm in its proximal segment. A C1 posterior arch excision with partial C2 laminectomy and clipping of the aneurysm was done.
Conclusion: Aneurysm associated with extracranial intra-dural PICA origin is a rare cause of SAH, and may not be detected with CT angiography. Such cases often require dedicated four vessel angiography, with careful study for any possibility of extra-cranial aneurysm. This variant has important surgical implication and requires preservation of the Lateral spinal artery (LSA-PICA communication), and that such aneurysm approached only with posterior cervical exposure without the need of a craniotomy. Such cases remind us the need to have an in-depth understanding of the variations of the posterior circulation.
Keywords: Extra-cranial; Intra-dural extracranial aneurysm; LSA; PICA; SAH.