Anterior Communicating Artery Aneurysm with Agenesis of Unilateral Internal Carotid Artery and Transcavernous Anastomosis

Abstract Internal carotid artery (ICA) agenesis is rare and clinically silent due to well-developed collateral circulation. We present an unusual case of ICA agenesis (Type D) with ruptured anterior communicating artery aneurysm. A 65-year-old female presented with a history of sudden onset severe headache and vomiting 1 day before admission, suggestive of subarachnoid hemorrhage (SAH). At presentation, the Glasgow Coma Scale was E3M5VT with WFNS Grade 4 and Hunt and Hess Scale-4. Noncontrast Computed tomography (CT) brain was suggestive of gyrus rectus bleed and SAH with intraventricular hemorrhage with hydrocephalus (Modified Fischer grade 4). A bone window in the CT brain showed the absence of the right carotid canal. Digital subtraction angiogram was performed, which showed agenesis of the right ICA with transcavernous anastomosis from the left cavernous ICA and anterior communicating artery aneurysm. An External ventricular drain was placed at 5 h of admission, followed by pterional craniotomy and clipping of the aneurysm. Postoperatively, the patient had vasospasm, which improved with intra-arterial nimodipine. At discharge, the Glasgow Outcome score was 3. Unilateral ICA agenesis with Transcavernous anastomosis presenting with subarachnoid hemorrhage due to ruptured anterior communicating artery aneurysm is an unusual presentation. Knowledge of such variants is important for planning the management of these aneurysms.