An unusual variant of the callosomarginal artery from the A1 segment of the anterior cerebral artery

BACKGROUND: Although the anatomy of the A1 segment of the anterior cerebral artery (ACA) is highly variable, a callosomarginal artery (CMA) arising from the A1 segment of the ACA is rare. CASE DESCRIPTION: A 27-year-old man presented with severe headache and was admitted to our hospital. Initial computed tomography (CT) showed subarachnoid hemorrhage in the basal cistern. Three-dimensional CT angiography revealed a saccular aneurysm arising from the left internal carotid bifurcation and showed an anomalous cortical branch originating from the left A1 segment of the ACA. The anomalous artery was interpreted as a CMA. CONCLUSIONS: Recognizing this variant preoperatively could be helpful in preventing complications of surgery. Careful follow-up studies are necessary in the present case to monitor the development of another aneurysm at the junction between the left CMA and the left A1 segment of the ACA.