The internal mammary artery as an alternative graft for internal maxillary artery-middle cerebral artery bypass: illustrative case.

BACKGROUND: Extracranial-intracranial revascularization has evolved to include bypasses using interposition grafts, most commonly the saphenous vein (SV) or radial artery (RA). These high-flow conduits are essential for treating giant or complex aneurysms, skull base tumors encasing the carotid or middle cerebral arteries, and selected cases of ischemic cerebrovascular disease requiring preservation or augmentation of cerebral blood flow. OBSERVATIONS: This report describes the first case of cerebral revascularization using the internal mammary artery (IMA) as an interposition graft. The patient had previously undergone endovascular treatment of an internal carotid artery aneurysm with a flow diverter and later developed progressive arterial stenosis leading to compromised distal cerebral perfusion. LESSONS: To achieve optimal outcomes and long-term patency, graft selection and bypass strategy must be planned meticulously, taking into consideration the patient's anatomy and specific clinical requirements. In the present case, because the RAs and SVs were unsuitable as primary grafts, the IMA was selected as a viable alternative for a high-capacitance internal maxillary artery-middle cerebral artery bypass. The graft was harvested through a minimally invasive thoracoscopic approach. Postoperatively, the patient exhibited significant clinical improvement, and perfusion CT demonstrated restoration of cerebral blood flow. https://thejns.org/doi/10.3171/CASE25888.