A 42-year-old woman presents with sudden severe headache, vomiting, and neck stiffness. Non-contrast CT shows diffuse subarachnoid blood. Cerebral angiography reveals a saccular outpouching at the junction of the anterior cerebral and anterior communicating arteries. The wall of such an aneurysm characteristically lacks which layer?

• A Endothelium
• B Media ✓
• C Internal elastic lamina
• D Adventitia

Explanation

Saccular (berry) aneurysms arise at bifurcation points of the circle of Willis where a congenital focal absence or attenuation of the medial layer allows progressive bulging under hemodynamic stress. Endothelium and adventitia are present; the internal elastic lamina is typically fragmented rather than absent. Rupture causes subarachnoid hemorrhage, the presentation described here.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.