LARGE ANEURYSM OF BASILAR ARTERY TIP MIMICKING MIDBRAIN TUMOR AND CAUSING UNILATERAL OBSTRUCTIVE HYDROCEPHALUS: A CASE REPORT AND TECHNICAL NOTE.

Cerebral ventricular system is a sporadic location of intracranial aneurysms including those of basilar artery tip. Treatment of such aneurysms remains challenging regardless of endovascular or microsurgical techniques applied. Basilar tip aneurysm presenting as third ventricular mass is rarely associated with obstructive hydrocephalus, mimicking midbrain expansive process and urging precise diagnostics and prompt treatment. Hence, the management of such patients may be delicate, having an uncertain outcome. We report on a case of a patient with unilateral hydrocephalus caused by large basilar tip aneurysm mimicking a midbrain tumor. We also discuss different operative strategies influencing the outcome, including our own endovascular treatment technical modification. A 62-year-old female patient presented with slightly decreased cognition, minor gait disturbances and urinary incontinence. Computed brain tomography revealed a third ventricle mass with unilateral ventricular dilatation, indicating hypertensive obstructive hydrocephalus. Magnetic resonance and digital subtraction angiography identified the third ventricular mass as a large saccular basilar tip aneurysm. The patient was selected for endovascular treatment followed by cerebrospinal fluid derivation. After aneurysm endovascular occlusion and temporary external ventricular drainage, the symptoms diminished and ventricular dilatation decreased. On post-procedure day 10, the hydrocephalus was relieved and external drainage removed. The patient recovered fully and was discharged without neurological deficit. In conclusion, large basilar tip aneurysms associated with obstructive hydrocephalus are rare and best treated by a combination of endovascular obliteration and cerebrospinal fluid ventricular diversion. The possibility of such an aneurysm should always be considered on the differential diagnosis of cerebral ventricular growths.