Background: An intracranial stump of an occluded vessel is a rare but important aneurysm mimic. We present 2 cases of middle trunk atresia of the trifurcated MCA, in which the proximal stump of the atretic vessel mimics an MCA bifurcation aneurysm in angiograms.
Case description: Both patients were referred to the authors with a presumptive diagnosis of an unruptured asymptomatic aneurysm at the MCA bifurcation that was found in an MR angiogram. The aneurysmal shape was conical in one case and in the other case, globoid and saccular. Careful examination of the catheter angiograms allowed us to notice the fine moyamoya phenomenon localized at adjacent M2 segments, in addition to the aneurysmal lesions. Surgical exploration revealed an MCA trifurcation instead of a bifurcation. The middle trunk of the MCA was atretic, showing a thin and white cordlike appearance, and its proximal end was a vascular stump instead of a true aneurysm. Adjacent M2 segments emitted fine perforating vessels in accordance with the moyamoya phenomenon at angiography.
Conclusion: In angiographic examinations, when an aneurysmal lesion is present at the MCA bifurcation in association with the moyamoya phenomenon at adjacent M2 trunks, the proximal stump of an atretic middle trunk of the MCA instead of a true aneurysm should be suspected and treated appropriately.