Isolated giant true intercostal artery aneurysm with arteriovenous fistula: A case report

Introduction

Intercostal artery aneurysm (IAA) is a rare disease. The causes of IAA include coarctation of the aorta, neurofibromatosis type 1 (NF1), Kawasaki disease, segmental arterial mediolysis (SAM), systemic lupus erythematosus (SLE), Ehlers-Danlos syndrome, and Loeys-Dietz syndrome.^1–3 The causes of intercostal artery pseudoaneurysm include thoracic trauma, iatrogenic injury due to thoracic surgery or thoracostomy tube, and mycotic infection.^4–6 We examined the case of a patient who had a right 11th IAA but the IAA cause was unknown, as he did not show signs of any clinical condition or disease that could cause IAA. We treated this non-ruptured isolated giant IAA with endovascular treatment (EVT), which is a minimally invasive procedure, and the outcome was successful.

Case description

The patient was an 83-year-old male. A right 11th IAA (size, 12 × 19 mm) was present in the paravertebral body, as depicted on computed tomography (CT) angiography findings 4 years ago (Figure 1(a)).OPEN IN VIEWER

The patient had several comorbidities, such as hypertension, dyslipidemia, chronic atrial fibrillation, and angina. He had no history of smoking. Blood tests were negative for β-D-glucan, antinuclear antibody, anti-double-stranded DNA antibody, and anti-Smith antibody. He had never been diagnosed with coarctation of the aorta, NF1, Ehlers-Danlos syndrome, Kawasaki disease, Loeys-Dietz syndrome, or SLE, which can cause IAA. In addition, he had no history of thoracic trauma, such as rib fracture, open thoracic surgery, thoracostomy tube, and mycotic infection, and no family history of Ehlers-Danlos syndrome. Segmental arterial mediolysis was also negative, as the IAA was an isolated aneurysm, and there were no dissections with alternating stenosis and aneurysms. Therefore, the cause of IAA was unknown. The patient underwent laparoscopic partial nephrectomy for right renal cell carcinoma 4 years ago (i.e. 2 months after IAA was observed on CT angiography) but there was no history of intrathoracic surgery. At 2 years after IAA was found, he underwent coil embolization for a left internal iliac aneurysm (size, 35 mm). Intercostal artery aneurysm grew progressively larger (2 years ago: size, 16 × 21 mm; 1 year ago: size, 20 × 25 mm; just before the treatment: size, 28 × 41 mm (Figure 1(b)–(d))). Just before EVT performance, the aneurysm was saccular, and a large amount of mural thrombus was observed in the aneurysm. The patient had no clinical symptoms. However, after considering the high risk of aneurysm rupture, we decided to perform EVT for IAA via the right femoral artery. Angiography revealed two outflow arteries from the aneurysm (Figure 2).OPEN IN VIEWER

However, the artery of Adamkiewicz was not observed in the outflow arteries of the aneurysm. An intercostal vein passed from the aneurysm to join the azygos vein with the IAA forming an arteriovenous fistula (AVF). Coil embolization was performed with an Interlocking Detachable Coil™ (Boston Scientific Corporation, Marlborough, MA) and a POD® Packing Coil (Penumbra, Inc., Alameda, CA). After performing angiography, we confirmed the occlusion of the IAA with endoleak, and that the treatment had been completed successfully (Figure 3).OPEN IN VIEWER

There were no clinical findings suggestive of spinal cord infarction after the procedure. The patient developed no complications and was discharged the day after the procedure. Endoleak was not observed, and the size of IAA at 1 month after the procedure was the same as that observed before treatment on CT angiography. Written informed consent was obtained from the patient for publication of this report.

Discussion

Intercostal artery aneurysm is a rare condition. To date, there are not many reported cases where IAA was caused by an AVF. After searching the PubMed database, we found that there were only 88 cases of patients with IAA. Of these, there were 33 (37.5%), 53 (60.2%), and two (2.3%) cases of true IAA, caused by an intercostal artery pseudoaneurysm, and had unknown causes, respectively. In addition, only seven of the 88 (8.0%) patients had IAA with AVF. Of these seven cases, five were of true IAA. To date, only one study reported a case of a patient with IAA caused by an AVF. ⁷ In our patient, AVF was considered to be the cause of IAA, but the cause of AVF development remained unknown. Aneurysm formation and inflow arterial dilation (size, 6 mm) were observed secondary to high flow associated with AVF. It is possible that the aneurysm grew at a relatively rapid rate in a short term.

Treatment options for IAA include open surgery and EVT. Arai et al. showed that coil embolization is a minimally invasive and safe procedure, and stent graft is required when distal blood flow needs to be maintained. ² In our patient, the artery of Adamkiewicz was not observed in the outflow vessels of the aneurysm on preoperative CT angiography. The inflow and outflow arteries were 6 and 2 mm in diameter, respectively. As small-diameter coronary stent grafts cannot be used for IAA cases in Japan, we did not use them to maintain distal blood flow, and we performed coil embolization instead. Yoshioka et al. showed that the origin of the artery of Adamkiewicz varies, but most commonly, this artery originates from the left intercostal arteries (80%) and between the 9th and 12th intercostal arteries (70%). ⁸ Treatment for IAA requires careful attention to the artery of Adamkiewicz. Bley et al. showed that ischemia due to occlusion of the intercostal artery caused a spinal cord infarction and subsequent paralysis in up to 13% of patients. ⁹ Our patient did not have any findings suggestive of spinal cord infarction or paralysis after treatment. However, when the spinal cord infarction risk is high, revascularization, such as stent graft, should be considered.

Carr et al. showed that true IAAs tend to have thin and fragile walls, especially in patients with hypertension; therefore, even a small aneurysm may have a high risk of rupture. ¹⁰ Nevertheless, there are no criteria for providing IAA treatment. Intercostal artery aneurysm is not an abdominal visceral aneurysm, but many abdominal visceral aneurysms (such as splenic and renal artery aneurysms) are recommended to be repaired or treated when it reaches a size of 20–30 mm, if not ruptured, according to the guidelines of “The Society for Vascular Surgery.” ¹¹ In our patient, the IAA grew gradually and reached a size of 28 × 41 mm before treatment. Therefore, we decided to treat the IAA because its size exceeded 30 mm, based on the criteria of the abdominal visceral aneurysm. Interestingly, our patient had a satisfactory course and successful outcomes.

In conclusion, AVF might have been the cause of IAA in our patient. Endovascular treatment for non-ruptured isolated giant IAA is a safe and minimally-invasive treatment. Although there are no clear criteria, this procedure might be beneficial when the size of the IAA exceeds 30 mm.