Endovascular Aneurysm Repair of Tuberculous Mycotic Abdominal Aortic Aneurysm on a Patient With Renal Transplant

Case Report

A 61-year-old gentleman of Pakistani origin was referred to the acute medical admission unit by his general practioner. He presented with an 8-week history of lower back pain, malaise, night sweats, and weight loss. He had end-stage renal disease, which was secondary to diabetes-induced nephropathy. He was initially receiving hemodialysis via brachiocephalic arterio venous fistulae. A year prior to his admission, he underwent live donor renal transplantation in Pakistan. Two months after his transplantation, serum creatinine began to rise and biopsy of the transplant kidney confirmed features of acute rejection. He was treated with immunosuppressants to control rejection. One month after this, he presented to the medical unit with urinary sepsis. He was on long-term immunosuppression with sirolimus 2 mg once daily and prednisolone 10 mg once daily. He was on insulin to control his diabetes and amlodipine for hypertension. Examination of the abdomen revealed mild tenderness in the epigastric region and marked tenderness in the left loin and lumbar regions.

A chest radiograph showed bilateral diffuse air space shadowing and an opacity in the right upper lobe. These changes were not present in the chest radiograph 2 months before. Magnetic resonance imaging scan of the spine showed an abdominal aortic aneurysm of 4.2 cm in the maximum diameter, a psoas collection and features of discitis at the L5-S1 vertebrae. Subsequent computed tomography (CT) angiogram showed complex ulcerated mycotic abdominal aortic and iliac artery aneurysms (Figure 1) with a contained rupture (Figure 2). Bronchio alveolar lavage was positive for acid-fast bacilli.

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Figure 1.

Computed tomography (CT) angiogram of the aorta with reconstruction.

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Figure 2.

Computed tomography (CT) angiogram in sagittal section showing contained rupture.

Presumptive diagnosis of tuberculus mycotic aneurysm was made on the evidence of widespread pulmonary tuberculosis (TB). He was barrier nursed and was treated with anti-tuberculous drugs—moxifloxacillin, isoniazid, pyrazinamide, and ethambutol initially for 1 month. Rifampicin interacts with sirolimus, hence the choice of moxifloxacillin. The liver function test worsened and was considered due to isoniazid. Isoniazid was changed to amikacin.

He was transferred to the vascular unit and underwent endovascular aneurysm repair (EVAR) using Talent stent graft (Medtronic, Minneapolis) bifurcated system. The main body of the graft was deployed via the left to minimize the ischemic time to the transplanted kidney. Postoperatively, there was a transient rise in the serum creatinine level. He was transferred back to the renal unit where he fully recovered. He was discharged home 2 weeks after his operation with an 18-month course of anti-TB medication.

Follow-up was done with 6 monthly clinic review, duplex scan, and yearly CT scans. Five years on, he remains free from graft infection, with reduction in sac size, without any endoleak, and with a functioning transplanted kidney (Figure 3).

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Figure 3.

Computed tomography (CT) angiogram at 5 years showing no evidence of endoleak and satisfactory endograft.

Discussion

The case report describes successful EVAR of a mycotic aneurysm involving the abdominal aorta. The presence of widespread TB on an immunocompromised patient and the presence of a transplanted kidney provided a unique challenge for the repair. Mycotic aneurysms are extremely rare, accounting for less than 1% of all aortic aneurysms. ¹ They usually occur in the elderly or immunocompromised patients. The most common causative organisms isolated are Staphylococus aureus, Streptococcus species, Salmonella, Pseudomonas, Escherichia coli, anaerobes, or fungi. Occasionally, TB mycotic aneurysms may occur. ² Tuberculosis can cause an aortic aneurysm either by eroding into the aortic wall from an adjacent area of infection or by direct infection of either the intima media or adventitial layer of the aorta. A review found that the former accounted for 75% of all TB aortic aneurysms. ³ The mortality rate for TB aortic aneurysms is high and symptomatic cases left untreated are invariably fatal. ³

The surgical options were open or EVAR. Open surgical options include resection and debridement of infected tissue and arterial reconstruction. Open repair has a higher mortality compared to EVAR. ⁴ Reconstruction is commonly done using an axillo bifemoral bypass graft ^5,6 or in situ replacement with vein or antibiotic-impregnated prosthetic graft. ¹ Cryopreserved arterial allografts can also be used with some success. ⁷ He was considered high risk for open repair due to widespread disease and immunosuppression. Open repair has an increased renal ischemia time compared to EVAR during cross clamping of the aorta. Various techniques can be used to protect the allograft during the procedure. The EVAR without allograft protection has been shown to be safe in the current literature. ^8,9 The endovascular options were aorto-uniiliac system with a femoro-femoral bypass graft or bifurcated system. Graft infection was considered to be high with the femoro-femoral crossover graft on an immunocompromised patient. An endovascular device that can be easily explantable should be chosen in case of a need for open surgery in future. A stent graft with less barbs or hooks is preferable in this scenario. ¹⁰ The endograft was soaked in rifampicin via the flushing ports prior to deployment. After flushing the endograft with heparinized saline, rifampicin 600 mg is mixed with 10 mL of saline and injected into the flushing port of the endograft. Successful endovascular repair of mycotic aortic aneurysm has been previously reported in the literature. ^{2,11 –16} A hybrid open-endovascular repair utilizing femoral vein can be an alternative option for mycotic aneurysms. ^17,18 However, due to the rarity of mycotic aneurysms the evidence base for the best long-term outcome between open and EVAR is lacking.

Medical treatment of the TB mycotic aneurysm is vital for successful outcome. In the presence of active infection, a period of medical therapy might reduce the chance of graft infection in future. Endovascular repair in the presence of pyrexia or active infection has a high risk of further infection. ¹⁹ The risk of rupture while on medical therapy can be ascertained using serial CT scans. Serial inflammatory markers and CT scans will determine the response to medical therapy. In a review of the literature on TB mycotic aneurysms, 87% of the patients offered both medical and surgical treatment survived, whereas in patients offered only 1 form of treatment or no treatment at all there were no survivors. ³ However, management in this case was complicated by the patient’s renal transplant and the attempt to preserve his renal function. The patient’s immunosuppressive medication was continued in order to protect the transplanted kidney.

In conclusion, EVAR is durable and safe procedure that should be used in some challenging cases where open repair is not feasible. Immunosuppressed patients with transplant having TB mycotic aneurysms are among those who would most benefit from the endovascular treatment.