Infundibulum of an Aberrant Accessory <scp>MCA</scp> Mimics Aneurysm

A 49-year-old man presented with episodic headache lasting 30 to 60 minutes and relieved by resting. He is a chronic smoker with an unremarkable past medical history. The physical exam was normal. Computed tomography angiogram (CTA) found suspected aneurysmal dilation (white arrow) at the A1 segment of the right anterior cerebral artery (ACA), the left A2 segment of the left ACA supplied by the right ACA through the anterior communicating artery, and the A1 segment of left ACA absent (Fig 1A). Diagnostic cerebral angiography was performed for further evaluation. Right carotid angiography showed small outpouching at the right A1 segment, corresponding to the CTA finding. A three-dimensional rotational angiography showed that the small outpouching was the left accessory middle cerebral artery (MCA) infundibulum instead of a genuine aneurysm. A small branch from its apex crossed the middle line, ran laterally to the left Sylvian fissure, and terminated at the prefrontal area of the left hemisphere, suggestive of a left accessory MCA (white arrowheads) (Fig 1B, Video S1). After supportive medical treatment, the patient's headache subsided. The accessory MCA is an uncommon anomaly of the MCA that arises from the ACA and passes into the Sylvian fissure along the MCA.1 The incidence of accessory MCA in angiographic and anatomical studies is reported to be 0.3 to 4.0%, and that of duplicated MCA is 0.2 to 2.9%.2 A previous study by Komiyama et al2 reported a consistent cortical supply by the accessory MCA to the anterior frontal lobe. Previous literature reported that the accessory MCA arises from the ipsilateral ACA. Infundibular dilation is funnel-shaped widening at the origin of a cerebral artery. A small perforator or cortical artery arising from its apex is crucial to differentiate from the aneurysm. This case showed an infundibulum over a rare anatomical variant of the accessory MCA, originating from the contralateral A1 segment of ACA. Such anatomical variant was not reported in previous literature. This case illustrated the importance of identifying vascular anomalies with operative or endovascular management implications. We thank the patient for providing permission to share his information. W.L. and N.M. contributed to the study concept and design; W.L., N.M., and X.T. contributed to data acquisition and analysis: W.L., N.M., B.Y. contributed to drafting the manuscript and preparing the figure and video. Nothing to report. Obtained. The data that supports the findings of this study are available in the supplementary material of this article. Video S1. On three-dimensional rotational angiography, a small outpouching was detected at the A1 segment of the right anterior cerebral artery. A small branch from its apex crossed the middle line, ran laterally to the left Sylvian fissure, and terminated at the prefrontal area of the left hemisphere, suggestive of a left accessory middle cerebral artery. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.