Chronic encapsulated mediastinal abscess presenting with remote cutaneous fistulization 12 years after redo aortic valve replacement for prosthetic valve endocarditis
© Kaul et al; licensee BioMed Central Ltd. 2006
Received: 26 May 2006
Accepted: 24 August 2006
Published: 24 August 2006
Chronic encapsulated mediastinal abscess is an unusual complication of previous open heart surgery. We report on the case of a 79 year old male who presented with epigastric fistulization of an encapsulated anterior mediastinal abscess 12 years after a redo aortic valve replacement for prosthetic valve endocarditis. The encapsulated abscess and its complex branching tracts and the cutaneous fistula were excised completely except the thin longitudinal strip of the ascending aorta which formed part of the posterior wall of the infected tract. This was covered with transposed greater omentum based on right gastroepiploic artery pedicle. Patient remains fit and well 2 years after his operation.
This report is unusual on account of the length of the interval between previous heart surgery and the infective complication, the presumed dormancy of the abscess for as long as 12 years, the complex course, branching tracts and the contents of the abscess, the remote fistulization of the abscess at a distant anatomical site and, finally, the principle of successfully covering an infected tract which formed the adventia of the ascending aorta with pedicled omentum in the hope of avoiding an ascending aortic replacement in a frail 79 year old man.
In the entire English language literature, this report represents the longest interval between a heart operation and a sternal or mediastinal abscess
Mediastinitis is a well known complication of open heart surgery. Chronic mediastinal abscess presenting years after the original heart operation is a medical curiosity. We report the unusual case of a chronic encapsulated mediastinal abscess presenting with cutaneous fistulization in the epigastrium 12 years following redo aortic valve replacement for prosthetic valve endocarditis
Serious sternal wound infection and dehiscence occurred in 1.86% of a study group of 2579 consecutive cardiac surgical procedures reported by Ottino et al . Stable et al noted a 1.5% incidence of sternal infection, mediastinitis and dehiscence amongst the 13,285 cardiac procedures that he studied . The CABG group had 1.7% and the valve group 0.7% incidence. In a five year audit, Upton reported 0.8%–2.3% post sternotomy mediastinitis with 79% cases caused by staphylococci . There are hardly any reports in English language literature of the incidence of postoperative mediastinitis after cardiac surgery in the absence of sternal wound infection or dehiscence. This is partly owing to the difficulty of obtaining a sample of mediastinal fluid in the presence of an intact sternum after the chest drains have come out. Theoretically, at least, one must assume there is a possibility that the anterior medistinal tissues could get infected while the overlying bone and soft tissues did not. Such a situation would obtain while operating on obviously contaminated tissues as for instance in endocarditis. Mediastinitis would then declare itself, acutely, either with systemic bacterial invasion and/or infected sternal dehiscence or, later and much more rarely, with a more circumscribed anterior mediastinal abscess .
What is unique about our patient is the 12 year dormancy of the abscess, absence of any clinical signs during this period and the eventual cutaneous fistulization remotely into the epigastrium. In search of the entire English language literature, this represents, to our knowledge, the largest interval between open heart surgery and a mediastinal or sternal infective complication. Mediastinal abscess, declaring itself after as long as 5 years after CABG, as remote complication of a retained pacing wire fragment, has been reported .
Cutaneous fistulization of a recent mediastinal abscess from descending necrotising mediastinitis with a cervical fistula has also been described . It is likely that in our patient, epigastric fistulization of the complex abscess with meandering branching tracts took place in a preformed tract formed by the retained pacing wire fragment.
Staphylococcal infection, in contradistinction to streptococcal infection, is known to predispose to the formation of encapsulated and localised infections. A particularly low grade infection could stay dormant for a long period of time. Another possibility to be kept in mind is a transient bacteraemia of unknown origin giving rise to a metastatic abscess in an old haematoma.
Although the inferior part of the abscess was completely removed, a small posterior longitudinal strip of the organised abscess cavity could not be removed as that would have mandated a complete ascending aortic replacement. This residual strip was covered by greater omentum transposed from abdomen on the right gastroepiploic pedicle. Postoperative infections of ascending aorta and transverse arch have been treated in a variety of ways including the use of viable omentum and muscle flaps [7–10]. Sternal spaces have been filled with rectus abdominis [11, 12], latissimus dorsi , trapezius , pectoralis major  and omental flaps [16–18]. There is evidence that omentum contains large number of immunologically active cells that accounts for its anti infective properties . We used the transposed omental pedicle in preference to pectoralis or any other muscle flap because of a number of reasons. First, geographically, the transposed omentum covered the whole of the space occupied by the excised abscess cavity from the mid aorta to the exit point in the left rectus. No other muscle flap, with the possible exception of a rectus abdominis flap, would have achieved this and the rectus flap wouldn't have been substantial enough. Secondly, since the sternum was healthy and was sought to be closed primarily and since it was the retrosternal dead space that was sought to be filled, any other muscle flap, except the rectus abdominis, would have interfered with the primary closure of the sternum. Also, the vascularity, the sheer spread and elasticity of the omentum were felt to be distinct advantages particularly when covering an obviously infected space.
Other pathologies that may present as anterior mediastinal masses postoperatively are mediastinal chylomas, saphenous vein graft aneurysms, ruptured pseudo aneurysms of aorta etc.
To conclude, mediastinal infections can masquerade in a variety of ways. Cutaneous fistulization of a chronic encapsulated abscess can happen years after surgery and requires complete excision of the abscess cavity and the fistulous tract and obliteration of the dead space by omental or muscle flaps.
We are grateful to Prof Mohan Sivanathan at the cardiac MRI department, Leeds General Infirmary for his help with the MR images.
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