A 26-year-old man was admitted to our department due to intermittent left hemiparesis for 3 months. Magnetic resonance image showed subacute infarction in the right precentral gyrus. Digital subtraction angiography and magnetic resonance angiography revealed an aneurysmal protrusion at the right middle cerebral artery (MCA) bifurcation. It was difficult to differentiate the aneurysm from the occlusion of the middle trunk of the MCA trifurcation. Brain single photon emission computerized tomography showed a decrease in perfusion in the right posterior frontal lobe without vascular reserve. Therefore, we planned a superficial temporal artery-MCA anastomosis with an exploration of the right MCA bifurcation. Intraoperatively, the aneurysmal opacification on preoperative angiography proved to be the proximal stump of the occluded middle trunk of the MCA trifurcation. An aneurysmal protrusion at the MCA bifurcation does not always indicate an aneurysm. In diagnosing protruding vascular lesions at the MCA bifurcation, the possibility of a vascular stump should be considered according to their angioanatomical appearance and the history of the patient.