Abstract 444: A Case of Continuous Clotting: A Rare Complication Following Flow Diversion

OBJECTIVE In‐stent thrombosis and strokes complicate up to 15% of neuroendovascular procedures. We present a rare case of recurrent in‐device thrombi following flow diversion, a complication of which the mechanism is poorly understood and sparsely studied. Methods Consented. CASEA 68‐year‐old female with history of coronary artery disease, hypertension, sick sinus syndrome status‐post pacemaker, atrial fibrillation, prior ruptured left posterior communicating artery aneurysm status‐post coil embolization that recanalized, underwent elective pipeline flow diversion of the left internal carotid artery (ICA) for aneurysm securement. Post operatively, she had right wrist weakness, and MRI revealed left hemispheric infarcts. She was discharged on aspirin and ticagrelor. On post‐operative day four, she presented with left middle cerebral artery (MCA) syndrome. CT brain demonstrated evolving left frontal strokes, and CTA demonstrated vessel patency. Given symptoms and concern for in‐stent thrombus she underwent cerebral angiogram which confirmed a left supraclinoid ICA sub‐occlusive thrombus within the pipeline flow diverter. She was placed on eptifibatide for sixteen hours followed by aspirin and ticagrelor. Two days later, she again developed left MCA syndrome and was found to have occlusion inside of the left ICA flow diverter. She underwent mechanical thrombectomy, with TICI 2c reperfusion and intra‐arterial eptifibatide. After a few minutes, follow‐up angiogram demonstrated recurrent thrombus for which aspiration thrombectomy was again performed. Given thrombus recurrence, dexamethasone was added to treatment for suspected immunogenic reaction to the flow diverter material. Despite aggressive interventions, the stent continued to re‐occlude, and the patient's condition deteriorated. She was placed on comfort care and passed away shortly thereafter. DISCUSSION Multiple factors are hypothesized to contribute to general thrombotic complications of endovascular procedures. Antiplatelet resistance, procedural length, complexity and multiple device use, patient age, aneurysm characteristics and location, device thrombogenicity, endothelial injury during embolization, device movement and malpositioning may be causative. However, repeated recurrent thrombi within a device may suggest an autoimmune or allergic reaction. Though not well‐documented in neuroendovascular literature, cardiology literature has described Kounis Syndrome. Specifically, Kounis Syndrome type III, which may precipitate vasospasm, plaque rupture or thrombosis secondary to mast cell and platelet activation, and cytokine release. The mechanism is poorly understood and may be confounded by a procedural contrast allergy, stent under expansion, malpositioning and vessel tortuosity, hypercoagulable state, cancer, and chemotherapy. Alternatively, a metal allergy to device metal alloys with nickel‐based components: cobalt, chromium and nitinol, may pose risk of thrombosis. Collective literature review neither supports nor rejects this hypothesis. One study suggests that nickel ions modulate the expression of ICAM1 on endothelial cells which recruits inflammatory cells. Another study suggests that the amount of nickel released is insufficient to induce hypersensitivity reactions. Furthermore, individual immune system variation may predispose some individuals to severe reactions to minuscule metal levels. Recurrent in‐device thrombosis following flow diversion is a rare but serious complication, of which the true nature of this phenomenon is not known. Further research is needed to clarify the underlying etiology and mechanism of this complication to facilitate early recognition, possible screening for, and treatment of this rare but significant consequence.