Mycotic aneurysm of the thoracoabdominal aorta in a child with end-stage renal disease

Abstract

A five-year-old child with nephrotic syndrome developed a mycotic saccular thoracoabdominal aortic aneurysm (TAAA) involving the visceral segment within a four month period following pneumococcal bacteremia and presumed spontaneous bacterial peritonitis (SBP). Due to continued aneurysm growth and progression to end-stage renal disease, TAAA repair was performed followed by cadaveric kidney transplantation. This is the first known instance of mycotic aortic aneurysm formation as a consequence of SPB and the first report of TAAA repair in preparation for kidney transplantation in a child.

Mycotic aortic aneurysms in infancy and childhood are usually the result of infected umbilical artery catheters, coarctation, or prior surgery.^1–3 Here, we present the case of a mycotic thoracoabdominal aortic aneurysm (TAAA) secondary to spontaneous bacterial peritonitis (SBP) occurring in a child with kidney disease.

CASE REPORT

The patient is a previously healthy male child who developed nephrotic syndrome at age four following a viral respiratory infection. Kidney biopsy demonstrated minimal change nephrotic syndrome without immune complex deposition. The child was treated with escalating regimens of intravenous (IV) steroids, cyclosporine, and diuretics, given persistent proteinuria, edema, and ascites.

At age five he was admitted to the hospital with fever, abdominal pain, and ascites and was found to have pneumococcal bacteremia presumed secondary to SBP. His symptoms quickly improved with IV antibiotics. Two months later he experienced a second episode of fever and abdominal pain and a computed tomography (CT) scan of the abdomen demonstrated soft tissue stranding of the mesenteric and presacral fat, but no abnormalities of the aorta. He was again treated successfully with antibiotics.

Four months later an incidental aortic aneurysm was identified on renal ultrasound, and follow-up magnetic resonance angiography confirmed a 3.0 cm saccular TAAA involving the visceral segment (Figure 1). No aortic wall thickening, thrombus, or peri-aortic stranding was noted. Potential causes of aneurysm formation in children were explored. The child had no stigmata of neurofibromatosis or connective tissue disease, and laboratory evaluation revealed no evidence of immune-mediated vasculitis. Given the rapid formation of the aneurysm following recurrent SBP and bacteremia, saccular morphology, and absence of other predisposing conditions, the aneurysm was presumed to be mycotic. Repair was initially deferred out of optimism the child’s renal function would improve to where he could tolerate surgery without being rendered dialysis-dependent. He was therefore discharged home on a four-week course of IV ceftriaxone and aortic surveillance with imaging every 1–3 months under the supervision of a vascular surgeon.

Figure 1.

Three-dimensional magnetic resonance angiography reconstruction demonstrating a saccular thoracoabdominal aortic aneurysm involving the visceral segment.

Over the next two years, surveillance imaging revealed progressive aneurysm growth to 3.8 cm in axial dimension, compared to an aortic width of 1.0 cm in neighboring segments. There was no evidence of inflammation of the aorta and the child remained free from systemic infection without the use of chronic antibiotics, suggesting the aortic infection had cleared. During this interval the child was placed on renal replacement therapy and was evaluated for transplantation. No living donor was available. Given the relative size and growth of the aneurysm, potential need for an abdominal kidney, and concern that aneurysm repair following transplantation would jeopardize the function of the graft, TAAA repair was considered mandatory prior to listing for transplantation.

At age eight (height 132 cm, weight 32.7 kg) the child underwent open TAAA repair via a left thoracoabdominal incision. A lumbar drain was placed pre-operatively and somatosensory and motor evoked potentials were monitored. Distal aortic perfusion was not performed given the low rate of spinal cord injury with aortic clamping in children.⁴ The left lung was collapsed using a dual lumen endotracheal tube. The diaphragm was partially divided circumferentially and the crura were partially divided to enlarge the aortic hiatus and expose the aorta proximally. The aneurysm was found to extend from the distal descending thoracic aorta to just below the renal arteries (Crawford Extent III/Safi Extent V; Figure 2, left panel). Several large peri-aortic lymph nodes in the region of the aneurysm were sent for pathology and culture. The aorta was clamped proximally and distally and opened. The left renal artery was ligated given an inconvenient location to the visceral vessels, and back bleeding from the right renal, celiac, and superior mesenteric artery (SMA) were controlled with Fogarty balloon occlusion. The aortic wall was inspected and appeared bland, with no evidence of active aortic or peri-aortic infection. The aorta was presumed to be sterile and a 14 mm Dacron graft was chosen for repair (Figure 2, right panel). The graft was selected to be slightly larger than the native aorta, which measured 12 mm proximally and 10 mm distally, to allow for future aortic growth. Following completion of the proximal anastomosis, the right renal artery, celiac artery, and SMA were incorporated into a visceral patch. The right renal artery was preserved given its close association to the other visceral vessels and because the child was not anuric. The distal anastomosis was performed and the clamp removed. Total aortic cross-clamp time was 26 minutes. Gram stain and culture of intraoperative specimens revealed no organisms. Histology of the aneurysm demonstrated intimal thickening with focal disarray and degeneration of medial elastin fibers without cystic medial necrosis. The lymph nodes exhibited reactive follicular hyperplasia.

Figure 2.

Intraoperative photographs demonstrating the aneurysm before (left panel) and after (right panel) repair using a 14 mm Dacron graft.

The patient was listed for transplantation following recovery from surgery, and two years later he underwent cadaveric kidney transplantation to the left iliac system via a standard hypogastric retroperitoneal approach. He recovered quickly with excellent graft function and normalization of serum creatinine.

DISCUSSION

Mycotic aortic aneurysms at pediatric age are rare, and reported causes include umbilical artery catheterization, coarctation, prior aortic or mediastinal surgery, embolization from bacterial endocarditis, direct extension from surrounding infected structures, or hematogenous seeding from infection at distant sites.^{1–3, 5–8} Aneurysm formation in our patient was likely the result of pneumococcal peritonitis, either from direct extension or hematogenous spread. Reported causes of mycotic aneurysms in children from direct extension have included mediastinitis, tuberculous para-aortic lymphadenitis, and perinephric abscess.^{5, 9, 10} Alternatively, bacterial aortitis from hematogenous seeding most commonly results from endocarditis, pneumonia, or osteomyelitis.^{7, 8} Our case represents the first reported instance of mycotic aneurysm formation secondary to SBP, although it remains unclear whether aortic infection occurred via direct extension from the peritoneal cavity or peri-aortic lymph nodes, or via hematogenous spread. Other factors which could have contributed to aortic instability in our patient include chronic steroid use and hypertension.

Aortic aneurysm repair prior to kidney transplantation has not been reported in the pediatric population. Both simultaneous and staged procedures have been performed in adults, with simultaneous operations reserved for cases when a living-related kidney was immediately available, or when aneurysm size was at the lower thresholds for repair.^{11, 12} Our patient’s aneurysm had increased in size from 3.0 to 3.8 cm over a two year period and significantly exceeded criteria for repair, measuring nearly four times the size of the uninvolved aorta with a saccular width of greater than 2.0 cm.^{13, 14} Repair was performed to prevent aneurysm rupture and facilitate kidney transplantation once there was no further hope of native kidney function recovery.

Prior pediatric thoracic aortic aneurysms have been repaired using homografts, autologous vein, Dacron patches, prosthetic interposition grafts, and aortic bypass.^15–18 The pediatric aneurysm literature is limited to case reports and small case series, precluding a meaningful evaluation of outcomes or conclusions regarding the ideal repair technique. Although avoidance of prosthetic material seems diligent in the setting of infection, multiple studies have demonstrated the safety of prosthetic conduits if actively infected tissue is absent or can be fully debrided.¹⁹ Furthermore, homograft use in adults is associated with calcification and delayed aneurysm formation from chronic rejection. Silver-coated Dacron grafts remain at risk of late reinfection.²⁰ Our patient had no evidence of active aortic infection, minimizing concern over placement of prosthetic material. The oversized interposition graft used should accommodate future growth and obviate the need for additional surgery.