Twin anterior cerebral artery anomaly: Azygous ACA with fenestrated right A1 segment

Clinical History

A 30-year-old hypertensive woman presented to the emergency room with complaints of acute onset of severe headache. Neurological examination did not reveal any abnormality. The patient was referred for NCCT (Non Contrast Computed Tomography) head followed by MDCT (Multidetector Computed Tomography) angiography of intracranial vessels.

Imaging Findings

NCCT head did not reveal any acute infarct/haemorrhage. MDCT angiography revealed fusion of A2 segments of ACA forming a single trunk suggestive of azygous anterior cerebral artery (ACA) (Fig. 1). Fenestration of the distal part of A1 segment of the right ACA (Fig. 2) was also noted. The rest of the intracranial vessels showed normal anatomy. There was no significant vascular stenosis or aneurysm.

Discussion

Anterior cerebral arteries (ACA) arise as terminal branches of internal cerebral arteries along with middle cerebral arteries. Many normal variants of ACA are known, however, co-existence of two variants is very rare.

Azygous ACA is formed by fusion of A2 segments into a single trunk [1]. As a result, there is no anterior communicating artery. Arterial fenestration refers to a vessel with a single origin dividing into two separate channels which rejoin distally. These are rare anomalies with a reported incidence of 0-5 % and 0-4 % respectively [1, 2].

Knowledge of normal variants of cerebral circulation is important as they are associated with increased risk of aneurysm formation and acute intracranial haemorrhage.

Azygous ACA and fenestrated ACA are rare anatomic variants of Circle of Willis with a reported incidence of 0-5%. Advancements in imaging with multidetector CT angiography play an important role in detecting these vascular anomalies particularly important during the neurovascular procedures.

Differential Diagnosis List

Final Diagnosis

Twin ACA anomaly with azygous ACA and fenestration of right A1 segment

URL:	https://www.eurorad.org/case/13901
DOI:	10.1594/EURORAD/CASE.13901
ISSN:	1563-4086