Objective and importance: We present a very unusual case in which a proximal posterior inferior cerebellar artery (PICA) aneurysm was located extracranially. We reviewed the PICA origin anatomy and pathology of aneurysms at this site. Clinical presentation: A Caucasian woman, 52 years of age, presented with a lesion at the craniocervical junction. She complained only of headache off and on without other symptoms. Her physical examination was unremarkable. A CT angiography clearly visualized an approximately 9-mm wide aneurysm of the right PICA which lay intradurally in the spinal canal at the C-1-level. Surgery was planned. However, six weeks after her initial referral and just before her surgical date. the patient suffered a subarachnoid haemorrhage. Physical examination at that time showed a lethargic but conscious patient, with slight disorientation (Glasgow Coma Score 14; Hunt and Hess grade III). Intervention: The aneurysm was successfully treated by microneurosurgical techniques via a suboccipital craniotomy with laminectomy of C, as well. Temporary clipping of the PICA was feasible and the aneurysm could be dissected and clipped appropriately. Conclusion: The present report underscores the anatomical variants of the PICA. Although uncommon, PICA aneurysms do occur and caretakers should be aware of this when treating patients with clinical signs or CT evidence of subarachnoid haemorrhage. Even extracranial PICA aneurysms can be encountered, either through a caudal loop or an early extracranial lateral medullary segment. We stress the use of four vessel angiography or CT angiography with thin cuts to rule out such aneurysms. (C) 2009 Elsevier B.V. All rights reserved.