Absent anterior communicating artery and varied distribution of anterior cerebral artery.

During the cerebral dissection of a 67-year-old male cadaver, a unique combination of variations at the circle of Willis and anterior cerebral artery (ACA) distribution were encountered. The A1 segment of both ACA were fused without an anterior communicating artery (ACoA), forming an X shape and giving rise to a common pericallosal artery (CPA), an incomplete distal ACA, and an incomplete distal anterior cerebral artery (IACA). The IACA had an unusual course, which may be important from the surgical point of view. The CPA continued as the A2 and A3 segments, and bifurcated into 2 pericallosal arteries. Branching patterns of the varied arteries to the interhemispheric region were evaluated, and results were discussed. Additionally, both posterior communicating arteries were hypoplastic. There was no aneurysm formation at the circle of Willis and its branches.