Total resection of an infected aortic arch aneurysm caused by Mycobacterium avium: a case report

Infected aortic arch aneurysms caused by Mycobacterium avium are very rare in immunocompetent individuals [1, 2]. Promptly recognizing these aneurysms is important because delays in treatment results in aneurysm rupture and a high fatality rate. Although Salmonella species, Streptococcus species, Staphylococcus aureus, and S. epidermis are commonly found in immunocompetent individuals, to our knowledge, infected aortic arch aneurysms caused by M. avium and their successful repair have not yet been reported. Here, we report a rare case of total arch replacement using a rifampicin-bonded gelatin-sealed woven Dacron graft for an infected aortic arch aneurysm resulting from M. avium.

After 1 month, he developed low-grade fever and chest pain, and a chest CT revealed a new saccular aneurysm of the aortic arch measuring 41 × 49 mm (Fig. 1a). He was continued on antibiotic treatment and closely followed; however, after 1 month a follow-up chest CT revealed that the saccular aneurysm had expanded to 43 × 62 mm (Fig. 1b), suggesting false aneurysm formation. 18F-fluorodeoxyglucose (FDG) positron emission tomography with CT (PET/CT) was also performed for suspected infective aneurysm, and this revealed FDG uptake in the aneurysm (Fig. 1c). Therefore, the patient was diagnosed with an infected aortic arch aneurysm due to M. avium.

Early surgical repair was deemed necessary because of the rapid expansion of the aneurysm. The options available were total arch replacement or thoracic endovascular aortic repair (TEVAR) with one or two debranching arch vessels as options. However, we opted to proceed with total arch replacement using a rifampicin-bonded gelatin-sealed woven Dacron graft because we strongly suspected an infective etiology. At surgery, median sternotomy was performed, and cardiopulmonary bypass was established via the femoral artery and the superior and inferior vena cava cannulas. Systemic anticoagulation was initiated with 300 units/kg heparin. Under hypothermic circulatory arrest at a pharyngeal temperature of 23 °C and a rectal temperature of 25 °C, the aortic arch was opened, and balloon-tipped selective cerebral perfusion cannulas were inserted. Balloon-occluded distal anastomosis was then performed under femoral perfusion of the lower body. The aneurysm was extensively debrided, and the resected section was sent for culture. Finally, the aortic arch was replaced with a rifampicin-bonded gelatin-shield 30-mm 4 branch woven Dacron graft (J Graft Shield Neo; Japan Lifeline Co., Ltd., Japan). Because of the presence of infected aneurysms near the origin of left subclavian artery, we could not perform in situ reconstruction of the artery and performed only extraanatomical reconstruction. The origin of left subclavian artery was closed, and the reconstruction was peripherally performed.

Postoperatively, no major complications were observed, and CT at the 14th postoperative day confirmed complete resection of the aneurysm (Fig. 2). M. avium was isolated from the resected tissue. The patient was discharged on the 15th postoperative day without incident and continued on the course of rifampicin 570 mg/day, ethambutol 750 mg/day, and clarithromycin 800 mg/day. He has received oral antibiotic therapy as an outpatient for 30 months with no symptoms, and we plan to continue them for several more months.

Nontuberculous mycobacteria are rarely pathogenic in immunocompetent individuals, but they are important pathogens in immunocompromised individuals [1, 2]. In immunocompetent individuals, aneurysm infections are typically with Salmonella species, Staphylococcus aureus, S. epidermis, or Streptococcus species. In our case, the patient had previously undergone radiotherapy and chemotherapy for malignant lymphoma, so will have developed a temporary immunocompromised status that could have accounted for his rare presentation.

CT is the standard tool for imaging suspected infected aneurysms. It provides a detailed assessment of the aneurysm and can offer morphological and anatomical images in high resolution. Periaortic fat, contrast enhancement, or fluid collections are clues to infection, but such features are not always prominent and may be missed in low-grade infection. In suspected cases that cannot be diagnosed by CT, diagnosis can be confirmed by 18F-FDG PET/CT [3], as in the current report.

TEVAR has been reported to have good results in the treatment of infected aneurysms. However, the risks of repeat infection are high after repair, not least because it requires that the stent graft be implanted in an infected aorta, and the procedure can be used for bridging to surgical repair [4]. Consequently, several permanent approaches have been reported to treat infected aortic aneurysms that use rifampicin-bonded grafts, homografts, or omental wrapping. Raman et al. reported an excellent outcome when using a rifampicin-bonded in situ graft for an infected abdominal aortic aneurysm due to M. avium in an immunocompromised patient [1]. Their patient was discharged on the seventh postoperative day and remained asymptomatic after 2 years of follow-up. In contrast, Tsilimparis et al. reported the use of a homograft for an infected abdominal aortic aneurysm caused by M. avium in an immunocompromised patient [2]. However, their patient developed multiorgan failure and had care withdrawn on the second postoperative day. Uchida et al. reported excellent results with the use of rifampicin-bonded and omental pedicle grafts in 23 cases of infected thoracic, thoracoabdominal, or abdominal aortic aneurysms [5], but their procedure was for mycotic rather than nontuberculous mycobacterial aneurysms. Some reports have reported good results with prosthesis made from bovine pericardium in the setting of infection [6].