Thoracoabdominal aorta replacement for multiple mycotic aneurysms caused by Hemophilus influenzae

CT and 3D reconstructions showing multiple thoracoabdominal aortic mycotic aneurysm.

Central Message.

A rare case of multiple mycotic thoracoabdominal aortic aneurysms caused by H influenzae, managed with replacement using 2 bovine pericardial tube grafts and left renal artery reimplantation.

Mycotic aortic aneurysms are an uncommon but severe condition characterized by infection of the aortic wall, leading to localized weakening and subsequent dilation. They account for 0.6% to 3% of all aortic aneurysms.¹ The term “mycotic” was used by W. Osler in 1885 to describe ulcerative appearances of the aortic specimens in infective endocarditis.² Mycotic aneurysms are associated with bacterial pathogens such as Staphylococcus aureus, Salmonella species, and Pseudomonas aeruginosa whereas infections caused by Haemophilus influenzae are extremely rare, with only a few documented cases.² The pathogenesis involves bacterial seeding of the arterial wall through hematogenous spread or contiguous infection, often in the background of atherosclerosis.¹

Blood cultures, and imaging, mainly computed tomography (CT) angiography, are essential for diagnosing and defining the extent of the aneurysm.^1,3 Management typically involves a combination of prolonged antibiotic therapy and surgical intervention, aneurysm resection, and subsequent reconstruction, to address both the infection and structural compromise.^1,3

Case Report

A 65-year-old female patient presented to a peripheral hospital with acute abdominal pain. After initial work up, a CT aortogram was performed and revealed a thoracic aortic intramural hematoma, left-sided pleural effusion, and uncomplicated diverticulosis, with no evidence of other aortic pathology. She was admitted with a provisional diagnosis of diverticulitis and was found to have acute kidney injury on blood testing.

Two weeks later, a follow-up CT aortogram demonstrated ileus-like changes, pleural effusion, and a 5.4-cm aneurysmal dilation of the descending thoracic and proximal abdominal aorta (Figure 1).

Figure 1.

Preoperative coronal, sagittal, and 3-dimensional computed tomography views showing extensive aneurysmal disease.

Pleural fluid analysis showed elevated protein level (41 g/L) and lactate dehydrogenase (177 U/L), raising suspicion for an infectious cause. Blood and pleural fluid cultures were both negative. Routine blood work revealed elevated inflammatory markers, with a white cell count of 16.7 × 10⁹/L and C-reactive protein of 142 mg/L. The patient was transferred to our center for further management.

At the time of admission, there was no clear evidence of a penetrating atherosclerotic ulcer. However, serial imaging revealed 6 saccular, rapidly expanding thoracoabdominal aneurysms ranging from 36 mm to 54 mm with severe aortic atherosclerosis and penetrating aortic ulcers, suggestive of impending rupture (Figure 2). Therefore, an urgent thoracoabdominal aortic replacement was indicated.

Figure 2.

Serial sagittal imaging of the aorta before and during admission.

Surgical Setup

Cannulation of the proximal descending aorta and the left common femoral artery was performed, followed by bicaval cannulation via the left saphenofemoral junction, Seldinger technique, and transthoracic echocardiogram guidance. Cardiopulmonary bypass with deep hypothermic circulatory arrest at 21 °C was undertaken with selective upper/lower body perfusion and selective visceral perfusion. Myocardial protection by deep hypothermia and systemic high-dose intravenous potassium was instituted. Spinal protection with cerebrospinal fluid drainage was performed. Thoracic epidural analgesia was administered.

Intraoperative Findings

Six discrete mycotic aneurysms involving coeliac axis, superior mesenteric and both renal arteries, multiple aortic wall abscesses, and severely calcified and friable aortic tissue were found.

Surgical Technique

To avoid infective complications related to use of the synthetic (Dacron) material, replacement of the thoracoabdominal aorta was performed using 2 bovine pericardial tube grafts fashioned over a Hegar dilator. After excision of the aneurysm, the first bovine tube graft was anastomosed to the descending aorta and trimmed distally. The second tube graft was beveled and anastomosed distally with the visceral segment of the aorta, and the left renal artery was reimplanted into it using a long saphenous vein graft. Then the 2 tube grafts were trimmed and connected (Figures 3 and 4).

Figure 3.

Replacement of the thoracoabdominal aorta using 2 bovine pericardial tube grafts.

Figure 4.

Postoperative coronal, sagittal, and 3-dimensional computed tomography views after thoracoabdominal aortic replacement with 2 bovine pericardial tube grafts.

Postoperative Course

Postoperatively, the patient required a prolonged course of antibiotics guided by the infectious disease team, with a transition from vancomycin and meropenem to daptomycin and ciprofloxacin, followed by ceftriaxone for 6 weeks. Two weeks after discharge, the patient presented to the emergency department with shortness of breath and bilateral proximal muscle weakness. She was diagnosed with a segmental pulmonary embolism on CT and bilateral subacute and acute strokes on magnetic resonance imaging, which were managed conservatively. Polymerase chain reaction testing of aortic specimens confirmed H influenzae as the causative microorganism, whereas histopathology results showed inflammatory changes consistent with mycotic aneurysms.

Discussion

We present a rare case of numerous rapidly enlarging mycotic aortic aneurysms on a background of chronic aortic disease precipitated by an unusual pathogen. Institutional review board approval was not required for this study; all patients provided informed written consent for the use of their clinical data and images for publication. Urgent thoracoabdominal aorta replacement with 2 bovine pericardial tube grafts was performed with an excellent outcome.

H influenzae is a Gram-negative bacterium recognized as a respiratory pathogen in adults. Our patient's chronic obstructive pulmonary disease increased her susceptibility to pulmonary H influenzae infection. Blood cultures were negative during this admission, consistent with reports of limited sensitivity for detecting this organism.⁴

Widespread calcified atheromatous plaques were identified on imaging of the aorta 2 years before admission. Such plaques have been documented as risk factors for bacterial seeding and mycotic aneurysm formation.⁵ The presence of extensive atherosclerosis in this patient likely predisposed her to infection in the setting of bacteremia and formation of the multiple aortic wall aneurysms within a short, 2-week period of time. However, it is not clear whether virulence, bacterial load, or preexisting atherosclerosis played the main role in this formation.

It is worth noting that H influenzae is a rare but recognized cause of infective endocarditis, representing an alternative etiology to more common pathogens. However, there was no evidence of endocarditis in this patient despite serial echocardiograms. Therefore as per Duke's criteria, the diagnosis of endocarditis would be “rejected.”

Rare pathologies will always present a diagnostic challenge. Patients with preexisting atheromatous disease of the aorta should be candidates for early cross-sectional imaging when presenting with nonspecific evolving symptoms. In addition, the data from the literature suggest an increasing spread of Gram-negative pathogens of the aorta in the current postantibiotic era, and our case may serve as an evidence of this process.

From a surgical perspective, this unique case of multiple mycotic aortic aneurysms demonstrates the effectiveness of prompt diagnosis and surgical intervention by replacement of the thoracoabdominal aorta with 2 bovine pericardial tube grafts and left renal artery reimplantation. A low threshold for referral to an aortic center should be exercised and early surgical intervention is advisable in such cases.

Conflict of Interest Statement

The authors reported no conflicts of interest.

The Journal policy requires editors and reviewers to disclose conflicts of interest and to decline handling or reviewing manuscripts for which they may have a conflict of interest. The editors and reviewers of this article have no conflicts of interest.