Aplastic or twig-like middle cerebral artery with the RNF213 variant: illustrative cases.

backgroundAplastic or twig-like middle cerebral artery (Ap/T-MCA) is a rare cerebrovascular anomaly characterized by unilateral stenosis of the proximal middle cerebral artery (MCA) with a plexiform arterial network along the horizontal (M1) segment, requiring distinction from moyamoya disease. Genetically confirmed cases remain rare. OBSERVATIONS: We report the cases of 3 patients with Ap/T-MCA carrying the RNF213 (ring finger protein 213) variant. The first patient, a man in his 60s, presented with subarachnoid hemorrhage. The second patient, a woman in her 20s, developed involuntary movement of the left upper limb. The third patient, the older sister of the second patient, experienced transient left hemiparesis in her 40s. In all patients, MR angiography demonstrated unilateral MCA abnormalities, and digital subtraction angiography revealed M1 stenosis with a plexiform arterial network in the subarachnoid space. All patients were managed conservatively, and targeted sequencing confirmed the RNF213 p.R4810K variant in each case. Only 2 Ap/T-MCA patients with this variant have been previously reported. LESSONS: The presence of the RNF213 p.R4810K variant in all 3 patients supports a relationship between twig-like MCA and the RNF213 variant. These findings suggest that Ap/T-MCA may represent the RNF213-related vasculopathy spectrum, and the occurrence in two sisters indicates a hereditary predisposition. https://thejns.org/doi/10.3171/CASE26186.