Background: We report a vascular abnormality of the middle cerebral artery (MCA) that has not been described in the literature before. Methods: Two patients (1 male and 1 female; age 44 and 67 years, respectively) were found to have a vascular abnormality in which the main trunk of the MCA had a twig-like form. Both patients presented with intracranial hemorrhage. Results: In these 2 patients, the abnormality was seen before the genu of the MCA. They had an intracranial hemorrhage due to an associated aneurysm inside the twigs. The twig appeared to be a network between the bifurcation of internal carotid artery and insular segment of MCA, and it was different from the collateral circulation due to acquired occlusion or moyamoya disease. Conclusion: This new type of vascular lesion of the MCA is not benign. It appears to be associated with the occurrence of an aneurysm, an important clinical aspect.
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