Twig-like middle cerebral artery

Last revised by Vitalii Rogalskyi on 11 Jun 2022

Twig-like middle cerebral artery or rete mirabile anomaly describes a discontinuity of a single trunk of the middle cerebral artery with several small vessels reconstituting the artery and giving it a twig-like appearance. Distally, normal vascular anatomy of the MCA branches need to be present and no signs of underlying stenoocclusive disease or moyamoya pathology of the distal internal carotid artery.

The incidence, which is very likely to be far less than 0.5%, remains unclear due to the absence of systematically applied criteria separating this condition from other vascular pathology of the region like (unilateral) moyamoya pattern.

The term "twig-like MCA" represents a hypothesis that this might be a form of aplasia with "rete mirabile" type reconstitution representing a residuum of the embryological MCA, which is formed by fusion of several small branches from the internal carotid artery 1,2.

This explanation is widely accepted, explaining other similar and more frequent MCA anomalies like MCA fenestration, in which, too, the distal ICA is unaffected. However, at the moment there is insufficient evidence that this angiographic condition really is a form of aplasia nor and how to rule out that a given case might be an acquired condition.

Future investigations into angiographic features distinguishing this condition from moyamoya syndromes and the clinical significance of those findings (regarding the outcome, risks of hemorrhage and ischemia) are needed.

There is some case-based evidence that twig-like MCA is associated with an increased risk of hemorrhage. When reviewing an angiogram with this condition, therefore, the presence of associated microaneurysms should be examined. 

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Cases and figures

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