We report a case of recurrent embolism, after the hemiarch replacement for acute Stanford type A aortic dissection. However, this was not clear on diagnostic imaging, including enhanced CT, and the embolic source could only be confirmed by angioscopy of the false lumen. To the best of our knowledge, this is the first report of such a case.
Eighty percent of re-operations after acute aortic dissection surgery are due to rupture, enlargement of aortic aneurysm, or re-dissection [1, 5]. Reports of embolism caused by a free-floating thrombus are rare [3, 4]. While believed to involve thrombi that formed in the false lumen owing to the antegrade blood flow of the residual dissection, some reported cases were diagnosed when other differential diagnoses were ruled out [4, 6]. In the present case, we searched for the source of the embolism; atrial fibrillation, cardiac tumor, or other factors were ruled out. CT and angiography showed antegrade blood flow from the distal part of the anastomosis to the false lumen. The large re-entry site at the left common iliac artery, and the three incidents of left lower extremity occlusion indicated false lumen thrombosis [1, 2]. Angiography showed blood flow from entry site into the false lumen stagnated in false lumen, therefore, we thought that blood flow from entry site might indicate a thrombus in the false lumen. However, in order to gain definitive diagnosis, we decided to perform angioscopy because a diagnosis could not be made using diagnostic imaging such as CT and magnetic resonance imaging (MRI).
Angioscopy has been covered by health insurance since 2016 in Japan. It is typically used to diagnose arterial diseases, along with CT and MRI; though angioscopy may lead to plaque and vascular damage. However, angioscopy can be used for invasive, direct observations of vessels ≥ 2 mm, including the thoracoabdominal aorta, and the subclavian, renal, iliac, femoral, and pulmonary arteries. These observations are performed to evaluate local arteriosclerosis; to assess the effects of treatment on an artery; for postoperative evaluations and follow-up; to estimate the timing of thromboembolism from pulmonary embolism ; and to check for tears or ulcer-like projection lesions in cases of aortic dissection [8, 9]. In the present case, angioscopy inserted into the false lumen of the aortic dissection tear was used to search for the embolic source. Complications of angioscopy include cerebral infarction, although rare , and the procedure is considered relatively safe. Intravascular ultrasound (IVUS) is also covered by medical insurance. The patient in this case had requested that the procedure be performed under local anesthesia. We had selected angioscopy for two reasons: first, the narrow diameter of the angioscopy sheath (5-Fr); second, we had thought that angioscopy would be more useful in investigating the cause of the thrombus, since surface texture can be ascertained by using it.
In addition, recurrent embolisms are sometimes encountered in cases of abdominal aortic aneurysms; however, these are usually discovered on CT, the typical finding of which includes the disappearance of a thrombus in an aneurysm. Therefore, in cases of chronic dissection, such as in the present case, it may be difficult to make a definitive diagnosis with CT. Therefore, to confirm whether the false lumen thrombus was consistent with embolic material, a catheter was inserted to obtain a sample of the thrombus. The pathological findings of the thrombus collected from the false lumen resembled the characteristics of free-floating thrombus. Thus, we diagnosed it as a thrombus that had become detached from the false lumen. Inserting the catheter directly into the false lumen allowed us to collect the tissue by suctioning the thrombus.
Anticoagulants reportedly improve embolisms caused by free-floating thrombi in chronic aortic dissection [4, 10]; however, surgery was undertaken in the present case because the patient experienced repeated embolic events, even though she was on oral anticoagulant and antiplatelet therapy. The purpose of the treatment was the prevention of the embolism, and it was necessary to close the entry site. In cases of an enlarged false lumen, re-operation with aortic arch replacement or debranching using thoracic endovascular aortic repair (TEVAR) can be considered; additionally, descending aortic replacement can also be considered to remove the source of the emboli. However, aortic arch and descending aortic replacement are both highly invasive procedures, and there are significant risks associated with re-operations. Stent-graft therapy with closure of the entry site is a minimally invasive and effective treatment. However, closure of the entry site alone does not shrink an enlarged false lumen; instead, it may continue to expand with an increased risk of rupture [1, 11]. A false lumen can be occluded using coil embolism, candy plug, vascular plug, or knickerbocker techniques [1, 12]. A therapeutic effect can be expected if complete exclusion of an enlarged false lumen is achieved . In the present case, it had been more than a year since the onset, and while the false lumen was partially thrombosed, the diameter of the aneurysm was only 35 mm. When embolizing via the true lumen, a 2-debranch TEVAR is necessary. Therefore, preemptive TEVAR was not indicated due to the absence of aneurysm enlargement , and TEVAR was judged to be over treatment in the present case.
The suppression of blood flow from the true to the false lumen may significantly reduce blood flow in the false lumen, thereby preventing the formation of an unstable thrombus and subsequent embolic events. Therefore, we believed that coil embolization of the false lumen was the best available treatment option. We had inserted two catheters, and used one of the coils as an anchor coil, without releasing it. We had performed coil embolization via the second catheter by maneuvering to wrap it around the anchor coil, to avoid migration. In addition, the patient had already undergone several surgeries in recent months and desired minimally invasive treatment under local anesthesia; hence, coil embolization of the false lumen was performed under local anesthesia. As a result, the false lumen blood flow and recurrent embolic events resolved. At the 1-year follow-up, the aneurysm was shrinking, and further embolisms have been prevented.