A Case of Thrombosed Giant Aneurysm of the Azygos Anterior Cerebral Artery: Clipping under Monitoring of Motor Evoked Potentials of the Lower Extremities

Giant aneurysms of the distal anterior cerebral artery (ACA), especially the azygos ACA, are rare. We treated a patient with giant aneurysm of the azygos ACA who underwent aspiration of thrombus and clipping under monitoring of motor evoked potentials of the lower extremities (L-MEPs), resulting in remarkable recovery of motor and intellectual function. A 72-year-old male was admitted with left motor weakness persisting for 2 weeks. Neurologically, disorientation and intellectual impairment were also noted. Imaging disclosed a 60-mm diameter aneurysm with heterochronous thrombi arising from the distal bifurcation of the azygos ACA. One month after the onset, radical surgery was scheduled. The azygos ACA was secured and the aneurysm was dissected, and the distal parts of the azygos ACA were confirmed. After removal of the thrombus, the neck was reconstructed with eight clips. L-MEPs disappeared due to occlusion of the azygos ACA for 20 minutes but reappeared after 22 minutes and normalized 78 minutes after reperfusion. Motor weakness improved entirely with mini-mental state examination score of 29 points at 1 month after surgery. One year later, Wechsler Adult Intelligence Scale-Third Edition and Wechsler Memory Scale-Revised scores reached normal levels. Review of reported cases found this aneurysm tends to occur in males in their 50s to 70s presenting with mass sign. Decompression of the aneurysm in the frontal lobe and monitoring of L-MEPs during temporary occlusion of the ACA are important.