Failure of Evolutionary Pruning: a Case Report on a Young Adult with Rare Twig-like Middle Cerebral Artery and Its Implications on Worse Outcomes

Twig-like middle cerebral artery (MCA) is a rare intracranial vascular pathology that was hypothesized to be an arrest on the evolutionary fusion of the plexiform arterial network in the forebrain into a single MCA artery. This anomaly predisposes affected individuals to worse outcomes such as intracranial hemorrhages due to its association with aneurysms and primitive plexiform arterial systems that are prone to rupture. In this case report, a 30-year-old male had a loss of consciousness after serving as a ceremonial guard for four straight days. The patient did not have any neurologic localizing signs but presented with occasional generalized headaches relieved by pain medications. Cranial MRA showed suspicious stenosis of the left MCA. A cranial computed tomography angiogram showed complete stenosis of the M1 segment of the left MCA. Digital subtraction angiography was also done, which confirmed the complete occlusion of the said segment with collaterals from the A1 of the anterior cerebral artery supplying the distal portions of the left MCA. These findings, hence, suggested the presence of a twig-like MCA. In this article, the prevalence, pathogenesis, arrival to the diagnosis, and clinical relevance shall be discussed.