INTRODUCTION: Posterior Inferior Cerebellar Artery aneurysms are rare and constitute 0.5 to 2% of total aneurysms in the brain. The majority of cases involve aneurysms in the proximal area of the vertebral artery from which the PICA arise (1). Distal PICA aneurysms are even rarer and account for approximately 0.3% of all PICA aneurysms. In a study done by Park et al, only five cases of distal PICA aneurysms were reported among 386 brain aneurysms making it a rare entity. They present typical computed tomography (CT) scan findings, but it can easily be overlooked on initial diagnosis.

CASE PRESENTATION: A 56-year-old female presented with a subarachnoid hemorrhage in the basal cisterns and CP angles associated with compression of the pons and intraventricular extension of the hemorrhage. CT angiography showed saccular, lobulated aneurysm measuring 5.9 x 4.7 x 4.6 cm with a narrow 2mm neck along the right PICA medullary-cranial loop junction accompanied by minimal focal vasospasm of the proximal medullary segment. Patient underwent coiling of the aneurysm. achieving subtotal filing of the aneurysm and there was complete preservation of parent arteries. The patient recovered without neurological sequelae.

DISCUSSION: PICA aneurysms commonly occur in patients in their 5th and 6th decades without gender predilection. The age and sex distribution of PICA aneurysms are similar to those of general aneurysms (1). Our case was in the 5th decade. Symptoms of PICA aneurysms are similar to those of subarachnoid hemorrhage. These symptoms include sudden onset of severe headache, sensorial changes, syncope and meningeal irritation. As in our case, the patient presented with severe headache followed by unresponsiveness. Non-invasive vascular imaging techniques are useful in detecting presence of aneurysm like 3D CT angiography and Magnetic Resonance Angiography. As in our case, a CT angiography became very useful in finding out the exact cause of the subarachnoid hemorrhage and in discovering the exact location of the aneurysm. Outcome of patients with ruptured distal PICA aneurysms is generally favorable; the incidence of rebleeding after rupture of a distal PICA aneurysm is higher than the rebleeding rate of Il intracranial aneurysms (78% vs 34%) (7).

CONCLUSION: When we are confronted with a case of subarachnoid hemorrhage in the fourth ventricle of unknown origin, particular attention should also be made to the distal PICA due to the rare occurrence of aneurysm in the said location.