A 70-year-old hypertensive man presents with sudden severe occipital headache, nausea, and nuchal rigidity. CT shows blood in the subarachnoid space. The most common cause in the Circle of Willis is an aneurysm at which site?

• A Bifurcation of the middle cerebral artery in the Sylvian fissure
• B Junction of the basilar artery and the superior cerebellar artery
• C Origin of the posterior inferior cerebellar artery from the vertebral artery
• D Junction of the anterior communicating artery (AComA) with the anterior cerebral artery ✓

Explanation

The anterior communicating artery (AComA) complex is the most common site for saccular (berry) aneurysms, accounting for approximately 35-40% of all intracranial aneurysms. The high hemodynamic stress at this bifurcation point (where both anterior cerebral arteries communicate) favors aneurysm formation. The internal carotid artery bifurcation (posterior communicating artery junction) is the second most common site (~30%), followed by the MCA bifurcation (~20%). AComA aneurysms on rupture may cause frontal lobe dysfunction, visual field defects, and hypothalamic disturbances. Anterior circulation aneurysms account for 85-90% of all intracranial aneurysms.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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