A rare case of ruptured intracranial aneurysm arising from the retro-mastoid branch of the occipital artery.

Background Aneurysms of the occipital artery (OA) are rare, with few cases published in the literature. The pathophysiology is unknown, and the presentation is variable. We present a case of a ruptured intracranial aneurysm arising from a branch of the OA. Case Description A 36-year-old male with a history of ankylosing spondylitis presented with altered mental status after an assaulted. On examination, he was intubated, with a Glasgow coma scale of 9, and imaging of the head and neck revealed a subdural hematoma of the posterior fossa and the cervical spine. The patient underwent suboccipital craniectomy and C1-5 laminectomy with the evacuation of the subdural hematoma. Postoperative cerebral angiography showed an intracranial aneurysm arising from the retromastoid branch of the OA on the left side. Furthermore, the parent vessel of the aneurysm supplied the left lower half of the cerebellar hemisphere. The aneurysm and the parent vessel were embolized using platinum coils. The patient tolerated the procedure well, and magnetic resonance imaging of the brain showed a minor left-sided cerebellar infarct, which was asymptomatic. The patient was discharged home with a modified Rankin scale of 2. There were no outpatient follow-up data available because the patient lost to follow-up. Conclusion Intracranial OA aneurysms are extremely rare with no clear consensus concerning the management of these aneurysms. They can be treated using endovascular and or open surgical techniques depending on the aneurysm characteristics, patient condition, rupture status, and others.