Asian Cardiovasc Thorac Ann 2006;14:e102-e105
© 2006 Asia Publishing EXchange Ltd
Mycotic Aortic Aneurysm Following Treatment of Pyogenic Vertebral Osteomyelitis
Siu-Bon Woo, MRCS,
Lik-Cheung Cheng, FRCS1,
Wing-Cheung Wong, FRCS
Department of Orthopaedics & Traumatology Kwong Wah Hospital
1 Division of Cardiothoracic Surgery, Department of Surgery, University of Hong Kong, Grantham Hospital, Hong Kong, China
For reprint information contact: Siu-Bon Woo, MRCS Tel: 852 3517 5058 Fax: 852 2709 2967 Email: ansonwoo{at}netvigator.com, Department of Orthopaedics and Traumatology, Kwong Wah Hospital, 25 Waterloo Road, Kowloon, Hong Kong, China.
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ABSTRACT
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Mycotic aortic aneurysm is a surgical emergency. However, its bizarre presentations could delay the golden hour of surgical reconstruction which is the mainstay of treatment. We report a case of mycotic aneurysm of the aortic arch which developed in the postoperative period after surgical treatment of pyogenic vertebral osteomyelitis at the lower thoracic level.
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INTRODUCTION
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Mycotic aortic aneurysm is a rare disease entity and remains a clinical challenge. Its non-specific presentations in a surgical patient in the early postoperative period could pose further diagnostic confusion.
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CASE REPORT
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A 67-year-old gentleman was admitted to the author’s unit with bilateral lower limb weakness and numbness of 2-month duration. On admission, he developed urine retention which required bladder catheterization. Physical examination showed diminished power and altered sensation of both lower limbs, together with loss of anal tone. He was afebrile on presentation. A set of plain radiographs of the thoracolumbar spine was taken. The radiographs revealed collapse of the T11 vertebra with destruction of the T10/T11 intervertebral disc (Figure 1
). Hematological investigations showed elevated white cell count (13.9 m·µL–1), erythrocyte sedimentation rate (122 mm·hr–1), and C-reactive protein level (106 mg·L–1). Blood culture yielded methicillin-sensitive Staphylococcus aureus (MSSA). Gadolinium-enhanced magnetic resonance imaging (MRI) was then arranged. It revealed increased signals over both T10 and T11 vertebrae with collapse of the T11 vertebral body in the T2-weighted images. There was also radiological evidence of epidural abscess formation that compressed the spinal cord (Figure 1). These investigations suggested a diagnosis of pyogenic vertebral osteomyelitis with compressive myelopathy.
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Figure 1. Plain lateral radiograph revealed the collapsed T11 vertebra with destruction of the T10/T11 intervertebral disc space (black arrows). An epidural collection that compressed the spinal cord was noticed on a sagittal T2-weighted gadolinium-enhanced MRI film.
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Cefuroxime and cloxacillin were administered intravenously (IV) and surgical debridement with anterior interbody fusion was performed 13 days after admission. The patient was placed in a lateral decubitus position and the lesion was approached via a left-sided posterolateral thoracotomy. A collection of 100 mL of turbid fluid was found inside the left pleural cavity and was drained intraoperatively. The T10/T11 intervertebral disc was necrotic with both adjacent endplates involved. Thorough debridement was performed until healthy graft-bed was visualized which allowed the insertion of a tricortical iliac crest graft. A chest drain was inserted. Debrided tissues were sent for bacterial culture which again yielded MSSA. Histopathological examination of the harvested tissue was suggestive of osteomyelitis.
The patient was clinically stable in the early postoperative period. The chest drain was removed on postoperative day 3 and a follow-up chest film was confirmed clear. However, he developed fever and left pleural effusion on postoperative day 10. Antibiotic therapy was changed to ceftriaxone IV to cover possible nosocomial pathogens. A sepsis work-up was undertaken and all tests were negative. Aspirates of pleural fluid were also sent for microbiological examination. There was absence of any growth of bacteria, fungi or acid fast-bacilli growth. The white cell count had escalated to 27.7 m·µL–1. On postoperative day 18, the patient had a sudden onset of hemoptysis, chest pain, and desaturation (SaO2 92.5%). A chest film was repeated which revealed persistence of left pleural effusion with a widened mediastinum. A computed tomography (CT) scan of the thorax was performed which showed dilatation of the distal aortic arch with surrounding hematoma formation. A false tract was noticed paralleling the aortic arch. A 5 cm soft tissue lesion was seen adjacent to the left side of the aorta on positive contrast enhancement, signifying blood collection. A left-sided hemothorax was also noticed (Figure 2). These investigations gave the impression of a ruptured aortic arch aneurysm.
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Figure 2. Contrast-enhanced CT revealed a false aneurysm (asterisk) that ran in parallel with the aortic arch. A contrast-enhanced 5 cm soft tissue mass (black arrow) was present next to the aorta. The picture is consistent with a leaking aortic aneurysm.
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The patient was immediately transferred to the cardiothoracic unit of a tertiary centre for emergency surgery. On arrival, the patient was in a state of clinical shock with a blood pressure of 80/30 mm Hg, and suffered an episode of convulsion. He was sent to the operation theatre immediately. Intraoperatively, the diagnosis of ruptured mycotic aneurysm was confirmed. The left subclavian artery was almost totally separated while the left common carotid artery was partially dehisced from the arch. The aorta was atherosclerotic. The false aneurysm had eroded into the left upper lobe causing the preoperative hemoptysis. The mycotic aneurysm was resected. Aortic continuity was re-established with a Hemashield conduit (Boston Scientific Inc., Natick, MA, USA) while the left subclavian and the left common carotid artery were re-implanted into the synthetic conduit without further augmentation with omentum or muscle flaps.
The procedure was performed under circulatory arrest in order to facilitate the contained ruptured of the mycotic aortic arch aneurysm, as the patient had developed shock prior to the operation with a sentinel sign of hemoptysis. Local application of antibiotics to the graft was not performed as potent antibiotics had already been administered intravenously.
Histological examination of the resected specimen revealed suppurative inflammation with fibrinopurulent exudates and a presence of colonies of gram positive cocci in the background of atherosclerosis. Blood culture also revealed methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa. The postoperative period was stormy as the patient developed disseminated intravascular coagulation, impaired renal function, and required tracheostomy for prolonged ventilation. Despite extensive antibiotic coverage, the patient’s condition further deteriorated and he died 17 days after surgery.
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DISCUSSION
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Mycotic aneurysm is a rare disease entity. The name was coined by Sir William Osler in 1885 because of its gross appearance of ‘fresh fungal vegetation’. It should be termed ‘infected aortic aneurysm’ as most of the offending agents are of a bacterial origin.1 In a large autopsy series, the prevalence of mycotic aneurysm was 0.7% of all forms of aneurysm.2 Mycotic aneurysms of the aortic arch or the thoracic aorta are even more uncommon3: only eleven cases were retrieved from the Mayo Clinic cardiac surgical database over a 25-year period.
Common pathogens causing mycotic aneurysm include Staphylococcus, Streptococcus, and Salmonella species.4 Virulence of pathogens and atherosclerotic aortic wall are two important factors in the formation of false aneurysm and subsequent leaking or rupture by weakening the aortic wall.3,4 Indeed, it is fatal if left untreated.5 Clinical presentation of thoracic mycotic aneurysm is non-specific6 and can sometimes be overlooked especially if the patient presents with concomitant clinical events that may add to diagnostic confusion.
Several modalities of imaging techniques have been utilized to detect mycotic thoracic aortic aneurysm. Contrast-enhanced computed tomography (CT) is the preferred choice in most series,1 and is readily available in most centers. It can also reveal associated conditions such as periaortic collection, aneurysmal rupture, and adjacent lung or vertebral pathologies. In addition, it is not operator-dependent as is transthoracic and transesophageal echocardiography (TTE/TEE). Conventional aortography, magnetic resonance imaging (MRI), and nuclear medicine examination have also been described in the medical literature.
Resection of the diseased aortic segment, thorough debridement, and restoring continuity are the principles of treating mycotic aortic aneurysm. Aortic reconstruction can be performed either in situ or extra-anatomical. The current trend is in situ reconstruction using prosthetic grafts which is described as a safe and durable procedure.7 The use of cryopreserved homografts with supplementary omentum and/or muscle flap coverage, currently unavailable in our locality, has also been reported in Europe.8 Extra-anatomical bypass is a theoretically sound method to minimize re-infection. However, it can still be associated with a high incidence of complications including re-infections, dehisced anastomosis, and stump ruptures.7 In some strategic areas such as the aortic arch, extra-anatomical bypass is technically impractical.
Pyogenic vertebral osteomyelitis can be associated with serious outcomes including paraplegia, tetraplegia, and death. It can also be associated with the formation of epidural abscess, psoas abscess, and paravertebral abscess. Surgical approaches depend on the site of maximal involvement. An anterior approach to the thoracic spine was adopted in this case. This allowed direct access to the infected disc and vertebral bodies, facilitating the insertion of an interbody strut-graft to achieve load sharing, thus achieving interbody fusion and spinal stability.
McHenry5, in his review of 70 cases of concomitant vertebral osteomyelitis and aortic lesions, suggested that male sex, atherosclerosis, diabetes mellitus, liver cirrhosis, and hypertension were common associated findings. Aortic infection can occur after vertebral osteomyelitis by different mechanisms including (1) bacteremia with seeding to the atherosclerotic aortic wall, which by itself fails to resist infection; (2) septic micro-embolization to the vasa vasorum, (3) direct inoculation during surgery; and (4) contagious spread from a septic focus such as a paravertebral abscess.
In our case, two possibilities accounted for the sequential occurrence of vertebral osteomyelitis and the aortic lesion. First, both clinical events manifested as two separate septic foci after a period of bacteremia, with one presenting earlier then the other. The other possibility is that the development of the aortic lesion was related to the treatment of the pyogenic vertebral osteomyelitis. The debridement procedure of the infected vertebral segments could inoculate seeding of microbes or septic micro-emboli to the diseased atherosclerotic wall. The preoperative MRI film showed a close proximity between the infected spinal segments and the descending aorta (Figure 3). There was, however, no radiological evidence suggestive of any focal aneurysmal dilatation of the descending aorta, even though the image of the aortic arch was unavailable. The patient developed pleural effusion approximately 10 days after surgery. That could be either an intraoperative contamination or progression of the infected pleural fluid that had not been sufficiently cleared. This collection could then become purulent and serve as a source of secondary infection.
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Figure 3. Gadolinium-enhanced axial MRI (with fat suppression) revealed the presence of paravertebral soft tissue infection in close proximity to the descending aorta (asterisk). There was no obvious focal aneurysmal dilatation.
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Surgical treatment of pyogenic vertebral osteomyelitis created additional channels to allow distant infection to the aortic arch. Direct invasion of the parietal pleura and then the adventitia of the aorta from the infected pleural space could be a potential cause. First, the patient had developed hemoptysis signifying the established communication. Second, CT scan revealed a contrast-enhanced mass with blood collection located adjacent to the false aneurysm. Third, histopathological examination revealed the presence of a suppurative inflammatory mass from the resected tissue at the false aneurysmal tract. While the chance of direct penetration of both the parietal pleura and the adventitia of the aorta by the microbes is relatively uncommon, bacterial translocation via the bloodstream remains the most likely cause. However, while the true sequence of events remains speculative in this case, one must bear in mind that both conditions can be fatal.
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REFERENCES
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- Miller DV, Oderich GS, Aubry MC, Panneton JM, Edwards WD. Surgical pathology of infected aneurysms of the descending thoracic and abdominal aorta: clinicopathologic correlations in 29 cases (1976 to 1999). Hum Pathol 2004;35:1112–20.[Medline]
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- McHenry MC, Rehm SJ, Krajewski LP, Duchesneau PM, Levin HS, Steinmuller DR. Vertebral osteomyelitis and aortic lesions: case report and review. Rev Infect Dis 1991;13:1184–94.[Medline]
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- Arbatli H, DeGeest R, Demirsoy E, Wellens F, Degrieck I, VanPraet F, et al. Management of infected grafts and mycotic aneurysms of the aorta using cryopreserved homografts. Cardiovasc Surg 2003;11:257–63.[Medline]
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ABSTRACT
INTRODUCTION
