Surgical Resection and Histopathological Analysis of a Thrombosed Giant Fusiform MCA Aneurysm After Initial Treatment with a Flow Diversion Construct

Background We describe the histopathology of an unruptured giant calcified left middle cerebral artery (MCA) fusiform aneurysm initially treated with endovascular flow diversion. The flow diversion construct underwent postoperative in-stent thrombosis, necessitating surgical resection of the aneurysm to eliminate mass effect. Methods A 75-year-old woman with a known left MCA aneurysm presented to the emergency department with moderate right hemibody weakness. Owing to the clinical and radiographic progression of the aneurysm, the patient was offered treatment. She was initially offered open surgical management of the lesion but declined it, indicating that she would consider only endovascular treatment. The patient underwent endovascular reconstruction of the aneurysmal segment with an overlapping pipeline construct. Postoperatively, the patient experienced in-stent thrombosis of the pipeline construct. The thrombosed aneurysm exerted a progressive local mass effect, necessitating en bloc surgical resection of the aneurysm and stent construct. The aneurysm was submitted for pathological analysis, which demonstrated chronologically older thrombus outside the flow diversion construct. Results Postsurgical imaging demonstrated a left MCA territory stroke. The patient gradually gained strength in her right hemibody. The histopathological analysis indicated that the degrees of platelet activation and clot formation in this case were dependent on the aggregate surface area of the thrombus and surface area of the pipeline device used in the reconstruction. Conclusions This technical report with histopathological analysis provides useful insight into the mechanism of aneurysmal thrombosis after flow diversion. It also raises new questions regarding the roles of thrombus formation, platelet aggregation, and stent construct surface area in the maintenance of vessel patency.