An Autopsy Case of Paradoxical Pulmonary Thromboembolism by Arteriovenous Fistula from Right Common Iliac Artery to Common Iliac Vein: A Rare Cause of Pulmonary Embolism

Background

Pulmonary thromboembolism (PTE) sometimes leads to a shock state and sudden death due to acute massive pulmonary arterial thrombosis and obstruction leading to acute right heart failure. Deep vein thrombosis (DVT) complicated by PTE has various etiologies, including congenital or acquired coagulation-fibrinolytic disorders, blood stagnation in major vessels, and injuries of major venous vascular walls [1]. We recently had a patient who suddenly died from PTE. An autopsy revealed a thrombus in the pulmonary artery derived from an arteriovenous fistula, with characteristics similar to those in the common iliac artery. We report this case as a very rare cause of PTE.

Case Report

A 74-year-old man was admitted to our institute because of dyspnea and cough. He reported loss of appetite and weight, with dyspnea on exertion and cough for 2 months prior to admission. Pulmonary fibrosis was noted on a chest X-ray 3 years prior to admission. He had a 100-pack-year smoking history and essential hypertension. On admission, his vital signs were as follows: body temperature, 37.6°C; pulse rate, 65 beats per min; blood pressure, 108/56 mmHg; respiratory rate, 20 breaths per min; and arterial oxygen saturation of 92% when inhaling oxygen from a mask with a 24% fraction of inspired oxygen (FiO2). Physical examination showed no anemia or jaundice, no jugular venous dilatation, and no leg edema. Auscultation revealed normal heart sounds and inspiratory fine crackles at the bilateral lower lung fields. There was no peripheral edema, abdominal bruit, or other lower-extremity abnormality. As shown in Figure 1, chest X-ray and computed tomography (CT) demonstrated a chronic fibrosing interstitial pneumonia pattern that gradually progressed within 1 week. Laboratory tests on admission revealed mild anemia (Hb 9.7 g/dL) and slight elevation of LDH and C-reactive protein, and moderately increased serum KL-6 and surfactant protein D, suggesting exacerbation of interstitial lung disease (Table 1). Unfortunately, D-dimer or other coagulation and fibrinolytic parameters were not measured. Electrocardiogram revealed no significant ST-T change and no severe right ventricular overload, as shown in Figure 2. Therefore, on admission we suspected that the patient’s dyspnea was due to respiratory impairment caused by interstitial pneumonia, and cardiac factors like right heart failure might have had a relatively low contribution.

The diagnosis of acute exacerbation of idiopathic interstitial pneumonia was made and corticosteroids were started: 20 mg/kg/day of methylprednisolone for 3 days, followed by 1 mg/kg/day of prednisolone. Low-grade fever and dyspnea on exertion were slightly improved by the 3rd hospital day. On the 4th hospital day, however, the patient had cardiopulmonary arrest on the ward, and he died despite cardiopulmonary resuscitation.

An autopsy revealed white emboli, which were massive but thin and organized, in the left main pulmonary trunk (Figure 2). Furthermore, microscopic vascular embolisms of pulmonary artery branches of both right upper and lower lobes, as well as left upper and lower lobes, appeared. These microscopic embolisms were thought to be fresh. The right common iliac artery was found to have an aneurysm that extended to the right common iliac vein to create an arteriovenous fistula (Figure 3). A significant thrombus, which was thought to have originated from a major vein, could not be found in the autopsy. A thrombus found in the right common iliac artery was macroscopically and histologically similar to an embolus in the left pulmonary trunk, with fine crystalloid nodules scattered throughout the thrombus (Figure 4). Although the origin of this crystalloid nodular lesion was not determined, it was suspected to be calcification. We concluded that the fatal PTE in this case was caused by paradoxical emboli that had passed through an arteriovenous fistula formed by penetration from the right common iliac artery to the vein.

Discussion

We reviewed our management of this case regarding the prediction and prophylaxis of PTE. An examination for a major abdominal vascular abnormality at the first patient visit or on admission, such as ultrasonography or CT with contrast, might have been useful. However, no pulsating mass or audible vascular bruit was found, and rescue therapy for acute exacerbation of idiopathic interstitial pneumonia with corticosteroids had priority. It is conceivable that the dyspnea on exertion and hypoxia in this patient were caused not only by interstitial pneumonia, but also by PTE. In clinical practice, however, it may be difficult to diagnose pulmonary arterial embolization complicated by an arteriovenous fistula, especially when other pulmonary diseases are apparent on routine physical examination and laboratory or radiological tests.

Acute PTE in association with DVT is considered to have 3 components: i) a congenital or acquired coagulation or fibrinolytic abnormality, ii) a disturbance of blood flow in the major veins, and iii) an injury of the vascular wall of a major vein [1,2]. In this case, we attributed the development of PTE to paradoxical embolization associated with an arteriovenous fistula from the right common iliac artery to the left common iliac vein, which is considered a very rare cause of PTE.

Arteriovenous fistulas are present in 0.2–1.3% of patients with an abdominal aortic aneurysm (AAA) and are found in 3–4% of patients with a ruptured AAA [3]. The inferior vena cava is the most common site of an arteriovenous fistula associated with an AAA, and the common iliac vein is the second most common site [4,5]. Reports of complications from major venous vessel embolization, in association with an arteriovenous fistula of the common iliac vein, are rare [4,6,7]. Furthermore, case reports describing complications of PTE have been rare [8–10], although a recent review [11] described not only a case report but also diagnosis by helical CT [12] and management with endovascular intervention [13,14]. Bridger reported an 83-year-old woman with a paradoxical PTE and thrombosis in a ruptured AAA involving the inferior vena cava that was diagnosed at autopsy [15]. However, a paradoxical PTE complicated by an arteriovenous fistula from the common iliac artery to the iliac vein, as in our case, has not been reported.

The embolus found in the left pulmonary trunk was histologically similar to the thrombus in the right common iliac artery, as fine crystalloid nodules were scattered throughout the thrombus and the embolus (Figure 5). Although the origin of these crystalloid nodules was not determined, they may have been due to calcifications that are often seen in atherosclerosis and arterial plaque. Similar reports have rarely described thrombi in histological detail. In this case, histology suggested that PTE was due to pulmonary arterial paradoxical embolization, with a thrombus passing from the right common iliac artery to the vein through an arteriovenous fistula, which had been formed by penetration from the iliac artery.

Conclusions

In this report, we have described an autopsy case of PTE due to paradoxical embolization with a thrombus in the common iliac vein. The thrombus had passed from the right common iliac artery through an arteriovenous fistula formed by penetration from the iliac artery to the vein, leading to sudden death. While it is very rare, clinicians should be aware of the possibility of paradoxical embolization, as in this case.