Surgical Management of Ruptured Mycotic Aortic Aneurysm Induced by Klebsiella pneumoniae

Mycotic aortic aneurysm (MAA) is a rare but severe condition, accounting for less than 1% of all aortic aneurysms. Despite advancements in antibiotic therapy, MAAs remain a critical concern due to their rapid progression and high rupture rates, which contribute to a poor prognosis. This case report details the successful surgical and medical management of a ruptured MAA caused by Klebsiella pneumoniae, a less common but highly virulent pathogen.

Case Presentation

A 63-year-old male patient presented with diffuse abdominal pain lasting one day. He was referred from a local clinic after a computed tomography (CT) scan revealed a ruptured abdominal aortic aneurysm (rAAA). The patient denied any history of hypertension, diabetes mellitus, hepatitis, or pneumonia. On admission, his blood pressure was 100/70 mmHg, with a pulse rate of 105 beats per minute and a body temperature of 37.1°C. Physical examination revealed a mildly distended abdomen with diffuse pain and tenderness, along with a palpable 5 cm × 5 cm pulsatile mass in the mid-abdomen.

Laboratory findings included a white blood cell (WBC) count of 10,600/mL, hemoglobin (Hb) of 92 g/L, hematocrit of 26.7%, serum creatinine (Cr) of 0.9 mg/dL, and C-reactive protein (CRP) of 10.24 mg/L. Initial chest radiography showed no pathological lung lesions. Abdominal CT confirmed a 5 cm × 5 cm ruptured infrarenal abdominal aortic pseudoaneurysm with a focally enhanced bulging contour.

Surgical Intervention

Given the critical nature of the condition, the patient was scheduled for emergency surgery. Under general anesthesia, a midline skin incision was made to access the retroperitoneal rAAA and hematoma. After clamping the infrarenal aorta and both iliac arteries, a significant amount of infectious material was observed in the perianeurysmal area and the aneurysmal wall. Culture tests were performed on tissue from the perianeurysmal area, thrombus, and aneurysmal wall.

Extensive local debridement and resection of the perianeurysmal tissue and aneurysmal sac were performed, followed by massive irrigation. An aorto-biiliac artery interposition was completed using a bifurcated polytetrafluoroethylene (PTFE) graft, reinforced with an omental flap.

Postoperative Management

Preoperatively and postoperatively, the patient was administered a third-generation cephalosporin as a preventive antibiotic until the causative microorganism and its antibiotic sensitivity were identified. Metronidazole was added for the first five postoperative days. Culture tests confirmed a heavy growth of Klebsiella pneumoniae, which was sensitive to most antibiotics except ampicillin. Tissue-Gram stain (Brown-Brenn stain) of the aortic wall was negative, and serologic and tissue tests for Salmonella species were also negative.

The patient received daily intravenous injections of a third-generation cephalosporin for four weeks. A serologic culture test performed three weeks postoperatively was negative. At four weeks postoperatively, the patient was discharged with a prescription for an oral third-generation cephalosporin for an additional two weeks. Follow-up CT at six months showed a patent PTFE graft with no recurrence of infection.

Discussion

Pathophysiology and Etiology

Mycotic aortic aneurysms are typically caused by the invasion of microorganisms into the arterial wall, leading to necrosis and rupture. The most common causative agents are Staphylococcus aureus and Salmonella, with Klebsiella pneumoniae being a rarer but highly virulent pathogen. Gram-negative microorganisms like Klebsiella pneumoniae are particularly concerning due to their ability to invade the normal intima and cause early aneurysm rupture.

The pathogenesis of MAA involves the necrosis and rupture of the atherosclerotic vascular wall, which facilitates microbial adhesion. Both embolization of microorganisms and iatrogenic factors can cause vascular endothelial damage, providing an opportunity for microbial invasion. Once the arterial wall is infected, it becomes fragile and unable to sustain systemic arterial pressure, leading to pseudoaneurysm formation and rupture.

Diagnostic Challenges

Early diagnosis of MAA is challenging due to its nonspecific symptoms and rapid progression. Imaging studies, particularly CT scans, are crucial for identifying the aneurysm and assessing its rupture status. In this case, the CT scan revealed a ruptured infrarenal abdominal aortic pseudoaneurysm, prompting immediate surgical intervention.

Surgical and Medical Management

The gold standard for treating MAA involves a combination of adequate antibiotic therapy and surgical resection with graft replacement. In this case, the surgical approach included extensive debridement of infected tissues, resection of the aneurysmal sac, and aorto-biiliac artery interposition with a PTFE graft. The use of an omental flap was intended to reduce the risk of graft infection.

Postoperative antibiotic therapy is critical to prevent recurrent infection. The patient received a third-generation cephalosporin for six weeks, with an initial addition of metronidazole. The choice of antibiotics was guided by culture and sensitivity tests, which identified Klebsiella pneumoniae as the causative agent.

Strategies to Prevent Recurrent Infection

Several strategies have been proposed to reduce the risk of recurrent infection in MAA patients. These include the use of pedicled omental flaps, silver-coated or antibiotic-soaked grafts, cryopreserved aortic allografts, bovine pericardial rolls, and vein grafts. Cryopreserved aortic allografts have been associated with lower reinfection rates, although their use remains controversial.

In this case, a classical PTFE graft was used due to the unavailability of alternative grafts. The patient’s postoperative course was uneventful, with no signs of recurrent infection or graft complications at six months follow-up.

Role of Endovascular Therapy

While open surgery remains the standard approach for ruptured aortic aneurysms, endovascular therapy is increasingly being considered for selected patients. Endovascular aneurysm repair (EVAR) offers the advantages of reduced surgical trauma and faster recovery. However, its use in infected aneurysms is controversial due to the risk of graft infection.

In this case, open surgery was performed due to the emergent nature of the condition and the presence of infection. However, the authors advocate for a more selective use of endovascular therapy in non-infected ruptured aneurysms, provided the patient’s status and aortic anatomy are suitable.

Preoperative Antibiotic Therapy

Preoperative antibiotic therapy is recommended to reduce intraoperative risks and postoperative infection recurrence. The duration of preoperative antibiotic treatment is typically between one to six weeks, although this remains controversial. Emergency surgery is indicated for uncontrolled infection or evidence of rupture, as was the case in this patient.

Conclusion

The management of mycotic aortic aneurysms requires a multidisciplinary approach, combining prompt surgical intervention with prolonged antibiotic therapy. Early diagnosis and appropriate treatment are essential to improve survival and prevent complications. In this case, the successful management of a ruptured MAA induced by Klebsiella pneumoniae highlights the importance of thorough debridement, appropriate graft selection, and extended antibiotic therapy.

doi.org/10.1097/CM9.0000000000000021

Was this helpful?

YesNo

0 / 0