Fenestrated azygos A2 segment: a rare anatomic variation

Advancement in neurovascular imaging has led to detection of abnormalities and normal anatomic variations. Most of anatomical variations in cerebral vasculature are asymptomatic and found incidentally; however, some may increase the risk of aneurysm formation and subsequent subarachnoid or intracranial hemorrhage. Here in, we report fenestration within an azygos A2 segment, as an incidental finding, which is an extremely rare anatomic variation in a patient suffering subarachnoid hemorrhage (SAH). However, there was no correlation found between SAH and the mentioned anatomic variation. To author’s knowledge this is the first report of such anatomic variation with providing source images of brain CT angiograms. Background The anterior cerebral arteries are devided into five segments: A1: from internal carotid artery (ICA) to the anterior communicating artery (A-comA). A2: from the A-comA to the region between genu and rostrum of corpus callosum where it bifurcates. A3: Bifurcation of A2 segment to pericallosal and callosomarginal which curves around the genu of corpus callosum and ends at the rostral part of body of corpus callosum. A4 and A5: distal branches on the superior surface of corpus callosum with anastomoses to distal branches of MCA and PCA. Fenestration of intracranial arteries was found on 0.3 to 0.9 % of cerebral angiograms, which is more common in posterior circulation and was claimed to be associated with saccular aneurysms. Although fenestration in anterior circulation is rare, azygos (unpaired) anterior cerebral artery (ACA) has been described in the literature as an anatomical variant. Here in we report the first case of fenestration within of an azygos A2 segment of ACA which is an extremely rare anatomical variation detected in brain computed tomography angiography (CTA). Case presentation A 22-year-old female suffered suddenly onset severe headache. She had Glasgow coma scale (GCS) of 15/15 and her neurologic exam was unremarkable. She was found to have subarachnoid hemorrhage (SAH) within left sylvian fissure on her brain computed tomography (CT) scan (Fig. 1). So a brain CT angiography with a 16slice multidetector scan was requested for her, which did not reveal any vascular lesion justifying SAH within left sylvian fissure. However we incidentally noticed a fenestrated azygos A2 segment in coronal images of maximum intensity projections (MIP) of her CTA (Fig. 2a, 2b). For determination of SAH source, she underwent a digital subtracted angiography (DSA) of brain 2 weeks later, which also did not show any aneurysms. Written consent was obtained from the patient to present this report and any images accordingly.