Hyperdense Aneurysm Visualized at the Occlusion Site During Thrombectomy: A Case Report

The occurrence of previously unrecognized aneurysms during mechanical thrombectomy for large-vessel occlusion poses a significant challenge. Aneurysms distal to the occluded vessel are often difficult to identify preoperatively despite the use of multiple advanced imaging modalities. However, important diagnostic clues may still be present even on plain CT scans. This case report describes a 79-year-old male who presented with acute left hemiparesis due to an occlusion of the right internal carotid artery. The aneurysm was identified intraoperatively but was not detected preoperatively. A retrospective review of the preoperative CT, however, demonstrated hyperdense findings that deviated from expected vascular anatomy. During thrombectomy, the aneurysm became apparent after deployment of the stent retriever, and the procedure was safely completed by withdrawing the stent retriever into the aspiration catheter while avoiding excessive mechanical stress on the aneurysm. This hyperdensity is believed to result from stagnation of blood flow within the aneurysm, caused by thrombus in the parent vessel. Successful recanalization was achieved without intracranial hemorrhage, and the patient demonstrated postoperative neurological improvement. Our findings suggest that careful review of preoperative imaging might have allowed earlier recognition. While hyperdense signs are generally considered indicative of thrombus, evaluating whether such findings conform to normal vascular anatomy may improve the preoperative detection of occult aneurysms.