Asian Cardiovasc Thorac Ann 2005;13:11-16
© 2005 Asia Publishing EXchange Ltd
Graft for Mycotic Thoracic Aortic Aneurysm: Omental Wrapping to Prevent Infection
Yukio Kuniyoshi, MD,
Kageharu Koja, MD,
Kazufumi Miyagi, MD,
Tooru Uezu, MD,
Satoshi Yamashiro, MD,
Katuya Arakaki, MD
Second Department of Surgery, Faculty of Medicine, University of the Ryukyus, Okinawa, Japan
For reprint information contact: Yukio Kuniyoshi, MD Tel: 81 98 895 1168 Fax: 81 98 895 1422 Email: kuni9244{at}med.u-ryukyu.ac.jp, Second Department of Surgery, Faculty of Medicine, University of the Ryukyus, 207 Uehara Nishihara-cho, Okinawa 903-0215, Japan.
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ABSTRACT
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Nine cases of mycotic thoracic aortic aneurysm were treated surgically between July 1995 and March 2003. The aneurysms were located in the ascending aorta in 1 patient, the descending thoracic aorta in 5, and the thoracoabdominal aorta in 3. Preoperatively, 3 patients were in shock due to rupture of the aneurysm. All patients underwent aneurysmectomy and in-situ graft placement. In 5 patients, the graft was covered with a pedicled omental flap to prevent postoperative graft infection. There were 2 hospital deaths: one patient died of multi-organ failure, and the other died from intrathoracic bleeding. After discharge, one patient died from intrathoracic bleeding 3 months after surgery. These 3 patients had not received omental wrapping. Postoperative graft infection did not occur in the 6 surviving patients during a mean follow-up period of 4.0 ± 3.1 years. It was concluded that covering the prosthetic graft with a pedicled omental flap may help prevent postoperative graft infection and improve the surgical results.
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INTRODUCTION
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Surgical treatment of mycotic aortic aneurysm is associated with more problems than that of a non-mycotic aneurysm, for a variety of reasons including increased risk of preoperative hemodynamic instability resulting from sepsis or aneurysmal rupture, and of postoperative graft infections. In-situ graft placement must be performed for anatomical reasons in the surgical treatment of mycotic thoracic aortic aneurysm (TAA), and the possibility of postoperative graft infection by contamination from the infected tissue around the mycotic TAA is higher than that for reconstruction by extra-anatomical bypass, such as in infrarenal mycotic abdominal aortic aneurysm. We describe 9 cases of mycotic TAA treated surgically during a 7-year period, and evaluate the potential role of omental wrapping of the prosthetic graft in preventing postoperative graft infection.
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PATIENTS AND METHODS
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Between July 1995 and March 2003, 211 patients with TAA were surgically treated in our hospital. Of these, 9 (4.3%) patients had a mycotic TAA. All available clinical information including administration notes, operation reports, pathology reports, laboratory data, radiology readings, discharge summaries, and follow-up evaluations were obtained from each patient’s chart and retrospectively reviewed. Three of the 9 patients with mycotic TAA were female and 6 were male; their ages ranged from 39 to 79 years, with a mean of 64.6 ± 11.6 years. The mycotic TAA was located in the ascending aorta in one patient, in the descending thoracic aorta in 5, and in the thoracoabdominal aorta in 3. In 7 patients, the aneurysm had either ruptured or was in a state of impending rupture and associated with severe pain; these patients underwent emergency surgery. Three of these 7 patients were in shock preoperatively, and 1 of those in shock suffered cardiac arrest just before the operation. The mean interval from diagnosis to surgery was 3.3 ± 5.6 days (range, 0–14 days). The diagnosis of mycotic TAA was established preoperatively in 6 patients (Table 1
). In these 6 patients, TAA was detected by computed tomography (CT) during detailed investigations for fever of unknown origin, and the diagnosis of mycotic TAA was based on the aneurysm morphology. The other 3 patients were diagnosed with mycotic TAA postoperatively, based on intraoperative findings (purulent fluid accumulation in the aneurysmal wall) and histological microscopic findings of the aneurysmal wall (identification of organism and neutrophilic infiltration). The pre-existing infections were urinary tract infection in 1 patient, direct spread from pulmonary tuberculosis and tuberculous thoracic spondylitis in 1, syphilis in 1, mediastinitis due to esophageal penetration by a fish bone in 1, upper respiratory tract infection or bronchitis in 3, and fever of unknown origin in 2 patients. Underlying disorders related to mycotic TAA were history of surgical excision for malignancy (rectal, laryngeal, or gastric cancer) in 4 patients, steroid therapy for systemic lupus erythematosus and hemodialysis for chronic renal failure in 1, and diabetes mellitus in 2. Bacterial cultures of blood were positive in 4 patients; the isolated bacteria are listed in Table 1. The preoperative maximal diameter of the aneurysm on CT ranged from 5.7 to 10.7 cm. On preoperative blood examination, the white blood cell count (WBC) ranged from 4,300/mm3 to 38,400/mm3, with a mean WBC of 14,357/mm3 ± 12,592/mm3. In 4 of the 9 patients, the WBC was below 10,000/mm3. The C-reactive protein levels ranged from 2.2 to 24.1 mg·dL–1, with a mean of 10.1 ± 7.6 mg·dL–1. As for the histological findings of the aneurysmal wall specimens, bacteria were identified in one patient. Microscopic examinations revealed neutrophilic infiltration as a histological finding of acute purulent infection in 4 patients. In the patient with tuberculosis, Langerhans’ giant cells and lymphocytes infiltrated the aneurysmal wall. In the patient with systemic lupus erythematosus, neutrophilic and lymphocytic infiltration was found.
All patients underwent complete resection of their mycotic thoracic aneurysms and in-situ graft placement under cardiopulmonary bypass as an adjunct to aortic clamping (Table 2). In 3 patients with a thoracoabdominal aortic aneurysm (TAAA), abdominal visceral perfusion was used during reconstruction of the major abdominal branches (celiac artery, superior mesenteric artery, renal arteries). In case no. 2 with TAAA, the second lumbar artery was reimplanted to prevent postoperative paraplegia. Case no. 9, with a mycotic ascending aortic aneurysm, underwent aneurysmectomy and graft placement with the aid of hypothermic total cardiopulmonary bypass (Figure 1). As the aneurysm in this case contained a considerable amount of purulent fluid, the operative field and graft were contaminated; therefore, the graft was packed with sponges soaked in 10% iodine solution, and the wound was closed only with skin. Change of sponges and irrigation of the mediastinum with saline diluted with the original iodine was continued for two days. On the 3rd postoperative day, the graft was wrapped with an omental flap, and the wound was closed completely (Figure 2).
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Figure 1. Enhanced computed tomography showing the ruptured pseudoaneurysm (P) from the ascending aorta in case no. 9. The part of the pseudoaneurysm wall that did not enhance was purulent fluid.
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Figure 2. Intraoperative photographs in case no. 9 showing (A) graft replacement of the ascending mycotic aneurysm, and (B) the graft wrapped with pedicled omentum (arrows).
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A woven graft was used in all patients. It was wrapped with an omental pedicled flap in 5 of the 6 patients who had been diagnosed with mycotic TAA preoperatively. Via a small upper median laparotomy, omentum was prepared for making a flap-like shape. In cases of descending aneurysm and TAAA, the omentum was incised on the right side and dissected towards the left side; the omentum was pulled into the left pleural space or the retroperitoneal space via a left subcostal hole or lienorenal ligament. In the case of ascending aortic mycotic aneurysm, the skin incision of the chest was elongated in the inferior direction for preparation of omentum. The greater omentum was incised on the left side and dissected along with the right gastroepiploic artery and veins. The prepared omentum was transferred through the retrosternal space.
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RESULTS
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Two patients died in the hospital (hospital mortality, 22.2%). One patient with a TAAA died of multi-organ failure on the 2nd postoperative day. He had undergone emergency surgery due to aneurysmal rupture and was in a state of septic shock preoperatively. After resection and graft replacement of the aneurysm, reconstruction of 4 major abdominal branches was carried out. The other patient had a descending TAA and suffered cardiac arrest just before the operation. He complained of right inguinal pain 3 days after the surgery and was diagnosed with a pseudoaneurysm of the right iliac artery by CT. He underwent resection of the pseudoaneurysm and graft replacement of the right iliac artery. Although it was suspected that this patient had multiple mycotic aneurysms due to sepsis, based on the intraoperative findings, the diagnosis of mycotic aortic aneurysm was confirmed by the presence of bacteria in the aneurysmal wall on histological examination 11 days after the first operation. As culture of the fluid around the aneurysm was negative, appropriate antibiotics could not be administered. Massive intrathoracic bleeding occurred suddenly and was suspected to be due to rupture of the anastomosis; the patient died 35 days after the first operation. Neither of these two patients had received omental wrapping of the implanted graft.
Postoperatively, 2 patients had wound infections, and one suffered pneumonia, although none of these patients were in a critical condition. There were no cases of postoperative paralysis nor of acute renal failure requiring hemodialysis. In the 7 hospital survivors, appropriate antibiotics were administered intravenously until the WBC and C-reactive protein levels normalized for a period ranging from 4 to 12 weeks (6.4 ± 2.7 weeks), followed by oral antibiotics on an outpatient basis or at another hospital. Five of these 7 patients were discharged and 2 were transferred to another hospital (Figure 3). In the late postoperative period, 1 patient died from massive intrathoracic bleeding at another hospital 3 months after the surgery. This patient had not received omental wrapping. One patient died from laryngeal cancer 3.9 years postoperatively. The remaining 5 patients have been well without any recurrences of their mycotic aneurysms on CT during follow-up of up to 6.9 years (mean, 4.0 ± 3.1 years). No postoperative graft infection occurred in the 5 patients who underwent omental wrapping.
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Figure 3. The white blood cell (WBC) counts and C-reactive protein (CRP) values were high preoperatively, decreased after surgery, and almost normalized by the time of discharge (n = 6).
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DISCUSSION
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The surgical results of mycotic TAA are still unsatisfactory because the operations are usually performed on an emergency basis while the patients are in a state of sepsis or shock from aneurysmal rupture.1 To reduce the surgical risk, stent-graft repair of a mycotic aneurysm has been proposed, but this remains controversial.2,3 Furthermore, patients face the risk of postoperative graft infection even if their emergency operations are successful. Although various operative procedures and devices for preventing postoperative graft infection have been reported, there is no definitive method of preventing such infectious complications. When the mycotic aneurysm is located in the thoracic aorta, it is anatomically difficult to perform an extra-anatomical bypass which is often applied to mycotic infrarenal abdominal aortic aneurysms. Thus, there is no method other than in-situ graft placement, and there is a high possibility of contamination of the prosthetic graft with this procedure.1,4,5 In Western countries, a homograft or allograft is available as an alternative. It is reported that biological grafts are generally more protective against infection than prosthetic grafts, although they are not always effective for mycotic aneurysms.6–8 In other countries, including Japan, where biological grafts are not always available; the postoperative prognosis depends mainly upon whether graft infections are successfully prevented.
In our study, 2 of the 9 patients died from probable rupture of the graft anastomotic site, which may have occurred as a result of graft infection. As these 2 patients were diagnosed with mycotic TAA by intraoperative findings, and the causative organisms were not identified even in the late postoperative period, neither appropriate antibiotic administration nor omental wrapping of the graft were performed. Both patients had undergone gastrectomy and did not receive omental wraps at the time of operation. Their deaths might have been partly due to insufficient infection control, although another major cause must be their preoperative shock states. For appropriate antibiotic administration, cultures of the infected tissues must be obtained during surgery, and identification of the pathogens should take place whenever possible.4 There are reports of the effectiveness of rifampicin-bonded grafts in preventing postoperative graft infections.9 Given that the target of rifampicin is Staphylococcus, this graft is not effective in cases such as methicillin-resistant Staphylococcus aureus or Escherichia coli infection.10–13 Even if these organisms are sensitive to rifampicin, a higher serum concentration of this drug would be necessary to prevent graft infection, as shown in animal experiments.14 As an alternative, Pasic and colleagues15 reported the effectiveness of antibiotic-releasing carriers (such as beads) that were placed near the graft in 4 patients; there were no operative deaths.
Various surgical methods of treating mycotic aneurysms have been reported with some success, but graft infections currently cannot be prevented entirely.1,4,5,15,16 Nakajima and colleagues16 described the original protocol for treating postoperative graft infections following mediastinitis. They re-explored the mediastinum, and the infected wound was directly disinfected by packing with sponges soaked in 10% iodine solution for 48 hours in patients with mediastinitis after graft replacement of ascending aortic and/or arch aneurysms. Thereafter, a tissue flap of omentum or muscle was placed around the prosthetic graft and in the dead space, to increase its effectiveness. We applied their method to prevent postoperative graft infection in case no. 9 with a mycotic aneurysm of the ascending aorta caused by Serratia marcescens. The graft was covered with omentum pedicled on the right gastroepiploic artery and vein before closing the sternum.
There are many reports concerning the effectiveness of using omentum to cover the graft as a means of preventing graft infection.5,17–20 Among the 5 patients in this study in whom an omental flap was used, 2 had TAAA, 2 had descending TAA, and one had an ascending aortic aneurysm. It was possible to transfer the omentum with the pedicle to the whole range of possible thoracic aortic aneurysm locations. Although it could not be verified definitely whether omental wrapping prevented postoperative graft infection as this study included a small number of cases, these results suggest that wrapping of the prosthetic vascular graft with pedicled omentum may be useful in preventing postoperative graft infection in cases of mycotic aneurysm.
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REFERENCES
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ABSTRACT
INTRODUCTION
