Though a rare complication of thoracic aortic surgery, the management of mycotic aneurysms and mediastinal infection remains a challenging surgical problem with high associated mortality. Early diagnosis is essential and should be considered in patients presenting clinically with signs of insidious sepsis such as persistent low-grade pyrexia or sternal wound infection following cardiac surgery. Early referral to a cardiothoracic centre is mandatory.
The treatment of mycotic aneurysms and infected arterial grafts poses special challenges to the cardiothoracic or vascular surgeon. The optimal surgical management is a subject of controversy (1). Without an operation, mycotic or false aortic aneurysms progressively expand, compress and erode the surrounding structures; they can rupture or remain a persistent source of infection or cause systemic embolism (2). The aim of surgery is excision of the aneurysm, aortic repair and eradication of infection.
A 61-year-old gentleman underwent an elective homograft aortic root replacement for congenital bicuspid valve that had become calcified causing severe stenosis. Seven weeks following discharge he presented to his local hospital with a superficial sternal wound infection, associated pain radiating to his right shoulder and spiking fevers. Blood cultures were positive for E-coli. Contrast chest CT (Figure 1) demonstrated a soft tissue mass containing a cavity that filled with contrast adjacent to the ascending aorta.
He underwent urgent repair of the mycotic aneurysm. This involved establishing partial cardiopulmonary bypass via the left common femoral artery and vein. In addition, a left mini-anterolateral thoracotomy was used to get access to the left ventricle and an apical vent was inserted to prevent over-distension of the ventricle. The patient was systemically cooled to 15 degrees centigrade and median re-sternotomy was carried out at low flow to reduce blood loss. Total circulatory arrest was established by stopping cardiopulmonary bypass and the false aneurysm was entered. The mycotic aneurysm was found to arise from the distal aortic homograft suture line but the aortic valve itself was intact and competent. The infected ascending aorta including the distal half of the graft was excised. A second aortic homograft was selected and the valve section removed then anastomosed to the arch. The aortic Arch was then de-aired a cross-clamp was applied and cardiopulmonary bypass was recommenced with re-warming of the patient. A third homograft was selected, the valve excised and anastomosed to join the original and second homograft. Cross clamps were removed and a single shock restarted the heart back into sinus rhythm. The sternotomy incision was extended to a superior laparotomy to allow mobilisation of the omentum from the transverse colon. The pedicled omentum was then brought up into the mediastinum and the chest and abdomen closed routinely.
The patient was taken to ITU and stayed there for 18 days. The main problem was severe global bronchopneumonia and weaning off the ventilator was difficult. Once out of ITU he mobilised quickly. There were no further signs of infection although he continued with another two weeks of antibiotics. By the time of discharge his inflammatory markers were completely normal. He remains well at 1 year.
Thoracic aortic pseudo- or mycotic aneurysms following aortic vascular surgery occur rarely but with high mortality. The case reported illustrates several important aspects in the diagnosis and management of such complications. Firstly, if mediastinitis is suspected following a thoracic aortic or cardiac procedure, the use of a contrast-enhanced chest CT may clarify the presence of an associated false aneurysm.
Secondly, at the time of operation prior to re-sternotomy femoral arteriovenous cannulation should be obtained and partial cardiopulmonary bypass established, allowing systemic hypothermic profusion. If in the event of torrential mediastinal haemorrhage on opening the sternum total circulatory arrest can then be used. In addition, placing a left ventricular apical vent while cooling the patient on cardiopulmonary bypass helps to reduce over-distension of the ventricle that can lead to mechanical damage to the myocardium and subendocardial ischaemia.
Thirdly, increasingly in the context of thoracic aortic mycotic anueurysms, in situ interposition of a vascular prosthesis is preferred over the use of an extra anatomical reconstruction 3. However, suture line complications and secondary graft infections may occur. The use of homograft aortic valves in the treatment of infective endocarditis is well established with excellent long-term survival of implanted cryopreserved cadervic valves. In the context of major vascular infection, cryopreserved arterial homografts allow safe in situ reconstruction, lower early and mid-term mortality and reduced antibiotic requirements (3).
Finally, vascularised, pedicled tissue flaps are commonly used to aid in healing anastomoses or to help eradicate and sterilize infected spaces. The use of omental flaps as opposed to conventional muscle flaps is often advocated in the presence of extensive mediastinal infection. In most cases an omental pedicle based on the right gastroepiploic artery can reach any location in the chest, its bulk and pliability allow it to fill irregular spaces and to closely adhere to high-risk anastomosis. In addition, it brings oxygenated blood to sites of ischaemia as well as various potent angiogenic factors (4).
Mycotic thoracic aortic aneurysms remain a surgical challenging, but with careful perioperative preparation, including the use of partial cardiopulmonary bypass, total circulatory arrest and hypothermic profusion, the use of cyropreserved cadervic interposition grafts and placement of pedicled omentum into the infected mediastinum, some of the inherent problems encountered may be overcome.
1. Pasic M, Carrel T, Vogt M, et al. Treatment of mycotic aneurysm of the aorta and its branches: the location determines the operative technique. Eur J Vasc Surg 1992;6:419-23
2. Katsumata T, Moorjani N, Vaccari G, et al. Mediastinal false aneurysm after thoracic aortic surgery. Ann Thorac Surg 2000;70:547-52
3. Vogt PR, Von Segesser LK, Giffin Y, et al. Eradication of aortic infections with the use of cryopreserved arterial homografts. Ann Thorac Surg 1996;62:640-5
4. Shrager JB, Wain JC, Wright CD, et al. Omentum is highly effective in the management of complex cardiothoracic surgical problems. J Thorac Cardiovasc Surg. 2003;3:526-532
