Anterior cerebral artery trifurcation with infraoptic origin and contralateral A1 segment absence

To describe an uncommon anatomical variant of the anterior cerebral artery and the imaging findings.

A 2-month-old infant with known history of atrial and ventricular septal defects was admitted to our institution for evaluation and management of growth failure. Given the clinical presentation and medical history, magnetic resonance imaging (MRI) of the brain and MR angiography (MRA) were performed to exclude congenital hypopituitarism and any vascular abnormality.

Time of flight MRA revealed trifurcation of the anterior cerebral artery with one of the vessels arising from the ophthalmic segment of the right internal carotid artery; thus, the A1 segment of the left anterior cerebral artery (ACA) was absent, and the right posterior cerebral artery (PCA) had a fetal origin.

Anatomical variants of the cerebral circulation are asymptomatic and found incidentally. Knowledge of these variants and careful examination of CT/MRI angiograms are important for diagnosis and treatment planning.