Nonaneurysmal Subarachnoid Hemorrhage Due to Unfused or Twiglike Middle Cerebral Artery Rupture: Two Case Reports.

BACKGROUND: An unfused or twiglike middle cerebral artery (MCA) is a congenital anomaly related to the abnormal development of the MCA. An unfused or twiglike MCA can cause both ischemic and hemorrhagic strokes. Previous reports have shown that an unfused or twiglike MCA with coexisting aneurysms can cause subarachnoid hemorrhage (SAH). CASES: Two patients presented with nonaneurysmal SAH due to an unfused or twiglike MCA. Both patients had stenosis of the proximal M1 segment of the left MCA and abnormal vascular nets distal to the stenotic lesion. Vasculature distal to the abnormal vascular nets remained grossly normal. These findings were not evident in computed tomography or magnetic resonance angiography.
CONCLUSION: An unfused or twiglike MCA can cause nonaneurysmal SAH. Digital subtraction angiography is necessary for accurate diagnosis.