Repeated Peripheral Embolisms associated with Chronic Aortic Dissection

Abstract

A male patient developed acute type B aortic dissection (AD) extending to the right external iliac artery (EIA) and left common femoral artery at the age of 56 years. Two months after the diagnosis of AD, he developed right renal infarction suggesting embolism, as the right renal artery arose from a false lumen containing a mural thrombus. Seven years later, at the age of 63 years, the patient was readmitted for acute onset of intermittent claudication in the right leg. On admission, arterial pulses distal to the right femoral artery were absent. The right ankle-brachial pressure index (ABI) was 0.66, while the left ABI was 1.06. Computed tomography (CT) confirmed chronic type B AD and revealed a localized occlusion of the right EIA and disappearance of a small protruding thrombus in the false lumen that was found on the previous CT, suggesting a second embolism. Since recovery of antegrade blood flow was insufficient after catheter embolectomy, femorofemoral bypass was performed with resolution of ischemic symptoms. Postoperatively, the ABI recovered to 0.99 in the right and 1.12 in the left, and CT showed a patent bypass graft and restoration of blood flow to the right leg. This case indicates that embolism should be recognized as one of the possible causes of acute organ ischemia in patients with AD, even in patients with chronic AD.

Aortic dissection (AD) can be complicated by rupture, aneurysm formation, valve dysfunction, or organ ischemia. Among these morbidities, ischemia affects approximately 30% of patients with AD, ^{1 2} and mostly occurs during the acute, not chronic, phase of the disease. The extension and expansion of a false lumen that compresses a true lumen is a main cause of occlusion of the aorta and its branches, ^{1 2 3 4} whereas ischemic complications attributed to other mechanisms are seldom identified.

In this paper, we report a rare case of chronic type B AD complicated with repeated peripheral embolisms due to fragmentation of a mural thrombus in a false lumen.

Case Report

Back in 2011, a 56-year-old man developed acute type B AD extending to the right external iliac artery (EIA) and left common femoral artery (FA) and was prescribed antihypertensive treatment (β-blocker, Ca antagonist, and angiotensin II receptor blocker) with bed rest. Two months after the diagnosis of type B AD, he presented with sudden back pain and hematuria. At the time, in addition to type B AD with a patent false lumen containing a mural thrombus, computed tomography (CT) revealed an infarction of the right kidney, suggesting embolism, as the right renal artery originated from the false lumen ( Fig. 1A–D ). The celiac, superior mesenteric, and left renal arteries arose from a true lumen on CT ( Fig. 1D ). Seven years later, at the age of 63 years, the patient was readmitted after presenting with acute onset of intermittent claudication, which started at a distance of approximately 10 meters and numbness in the right leg. He was still under regular treatment for hypertension and his blood pressure was 152/72 mm Hg with a pulse rate of 78/min. Arterial pulses distal to the FA were absent in the right leg, but pulses in the left leg were palpable. The right ankle-brachial pressure index (ABI) was 0.66, which was significantly lower than the 0.97 value measured 7 months previously, while the left ABI was 1.06, almost equal to the previous 1.13 ( Fig. 2 ). An electrocardiogram (ECG) revealed normal sinus rhythm and no ischemic signs. Transthoracic echocardiography showed normal ventricular and valve function and no intracardiac thrombus. CT confirmed chronic type B AD and revealed a localized occlusion of the right EIA and a patent right FA ( Fig. 3A and B ). The CT also revealed the absence of a small protruding thrombus on the mural thrombus in the false lumen that had been presented on the previous CT ( Fig. 3C ). No occlusions or stenotic lesions attributed to atherosclerosis were present in the distal arteries in either leg. These findings implied embolism of the EIA. After unsuccessful anticoagulant therapy, urgent surgery was scheduled. The right common FA was examined during surgery and, although there was no false lumen, a small fresh thrombus was discovered. After catheter embolectomy, favorable retrograde blood flow was obtained through the superficial and deep femoral arteries; however, recovery of antegrade blood flow was insufficient. A femorofemoral bypass grafting was then performed using a prosthetic vascular graft. Postoperatively, intermittent claudication in the right leg was resolved, and the ABI recovered to 0.99 in the right and 1.12 in the left. Postoperative CT showed a patent bypass graft and restoration of blood flow to the right leg. The patient was discharged without symptoms of limb ischemia on postoperative day 7, and is doing well 1 year after the operation.

Fig. 1.

( A , B ) CTs showing infarction at the lower pole of the right kidney; ( C ) the right renal artery arising from the false lumen; ( D ) and the left renal artery originating from the true lumen. CT, computed tomography.

Fig. 2.

( A ) ABIs obtained 7 months prior to hospitalization, ( B ) preoperatively, and ( C ) postoperatively. ABI, ankle-brachial pressure index; ECG, electrocardiogram.

Fig. 3.

( A , B ) CTs on admission showing chronic type B AD extending from the thoracic descending aorta to the right EIA and left common FA (A, left anterior oblique view) and occlusion of the right EIA and the patent right FA. ( C ) Previous CT showing a small protruding thrombus (arrow) on a mural thrombus in the false lumen. AD, aortic dissection; CT, computed tomography; EIA, external iliac artery; FA, femoral artery.

Discussion

Approximately one-third of patients with AD are complicated by visceral, renal, spinal cord, and/or limb ischemia, which increase the risk of early death. ^{1 2} Most ischemic complications occur during the acute phase of the disease, and are rare in patients with chronic AD. The main mechanism of ischemic complications is compression of a true lumen by extension and expansion of a patent false lumen, inducing occlusion, or thrombosis in the aorta or branch arteries. ^{1 2 3 4} However, in our patient, renal infarction and leg ischemia occurred in the chronic phase of type B AD and resulted from embolism. According to a systematic review of 138 patients with type B AD and lower limb malperfusion (LLM), the LLM developed in the chronic phase in only four patients (3%) and in the acute phase in 134 patients (97%), and no case of LLM caused by embolism was reported. ⁵ Vascular obstruction caused by mechanisms other than compression of a true lumen has been previously reported in a few cases of both acute and chronic AD. In acute type A AD, DeBakey and Lawrie ⁶ described a case of obstruction of the arch vessels due to intussusception of the detached intima from the ascending aorta into the distal aortic arch. Lévy et al ³ described acute thromboembolism in the upper or lower extremities in three patients. Furthermore, Schraft and Lisa ⁷ described an autopsy case of multiple peripheral organ and vascular embolisms. In chronic type B AD, Nakahira and colleagues ⁴ reported two patients with leg malperfusion arising due to the movement of the intimal flap with postural changes, and Arata and colleagues ² described a case of leg malperfusion by walking exercise. However, unlike these reported cases, in our patient, peripheral embolism related to the thrombus in the false lumen caused renal infarction and leg ischemia.

Ischemic symptoms in our patient suggested renal and vascular embolisms which were confirmed by CT. However, in the case of acute onset of isolated lower limb ischemic symptoms, differentiation of peripheral arterial embolism from LLM syndrome can be difficult. Clinical characteristics of our patient with peripheral embolisms and patients with LLM described in the systematic review ⁵ are summarized in Table 1 .

Table 1. Clinical characteristics in patients with type B AD and lower limb malperfusion and the present patient with type B AD and arterial embolism.

	Patients with LLM ( n  = 138) a	Present patient with embolism
Age (y)	58 ± 12	63
Sex	Male (87%)	Male
Development of LLM	Acute phase (97%)	Chronic phase
Clinical presentation	Acute limb ischemia (87%) Bilateral (56%)	Acute intermittent claudication Unilateral
Symptoms	Pulse defecit (100%) Chest pain (42%) Back pain (45%) Abdominal pain (13%)	Pulse deficit (+) No No No
Associated malperfusion b	Renal (53%) Celiac (31%) Superior mesenteric (34%)	No
Treatment	Medical (16%) Surgical (37%) 30-d mortality of 14% Endovascular (47%) 30-d mortality of 8%	Surgical

Abbreviations: AD, aortic dissection; LLM, lower limb malperfusion.

^a Reported patients in the systematic review by Gargiulo et al. ⁵

^bMalperfusion by radiological imaging.

Concerning the source of an embolus and the pathogenic relationship between the embolism and AD, Schraft and Lisa ⁷ have suggested that multiple distant embolizations developed due to mural thrombi located at the site of intimal rupture based on autopsy findings. On the other hand, Levy and colleagues ³ have speculated one possible causative mechanism of migration of an embolus from the false lumen to the true lumen through a reentry, but autopsy findings of their patients were not compatible with their speculation. However, embolization of biological glue used for repair of AD causing acute limb ischemia has been recently reported in some patients. ⁸ In these cases, escape of glue particles through a reentry at the distal site has been proposed as one probable mechanism for peripheral embolization of glue particles. ⁸ In the first ischemic event in our patient, the renal infarction occurred in the right kidney which was perfused through the artery arising from the false lumen containing the thrombus. In the second event, CT demonstrated the localized occlusion of the EIA and the disappearance of the small protruding thrombus. Of these two ischemic events, fragmentation of the mural thrombus in the false lumen is the probable source of the emboli and fragments of the thrombus, as emboli would have directly blocked the branch of the right renal artery through the false lumen in the first embolism, whereas escape of fragments of the thrombus from a false lumen into a true lumen through a reentry may have led to embolic occlusion of the EIA in the second embolism.

Conclusion

We report a case of repeated peripheral embolisms associated with chronic type B AD. Fragmentation of the mural thrombus in the false lumen would be the causative mechanism of repeated peripheral embolisms in our patient. This case indicates that embolism should be recognized as one of the possible causes of acute organ ischemia in patients with AD, even in patients with chronic AD.