Poststernotomy Wound Infection: Role of CT Scanning in Diagnosis and Staging
ABSTRACT & COMMENTARY
Synopsis: Computerized tomography is a useful technique in the detection and staging of poststernomy infections.
Source: Gur E, et al. Clinical-radiological evaluation of poststernotomy wound infection. Plast Reconstr Surg 1998;101: 348-355.
Gur and colleagues in tel aviv reviewed the role of computerized tomography (CT) in the diagnosis of poststernotomy wound infection in 160 patients seen at their institution between 1984 and 1993. The CTs were read by a radiologist without knowledge of the ultimate diagnosis. The diagnosis was surgically confirmed in each of the cases.
The overall sensitivity of CT diagnosis was 93.5%, while its specificity was 81.7%. CT was highly accurate in the detection of osteomyelitis of the sternum. The sensitivity of detection of involvement of the anterior sternal plate was 92.8% and specificity was 96.2%; the comparable results for detection of posterior plate involvement were, respectively, 93% and 85.1%. The sensitivity and specificity of CT in the detection of mediastinitis were, respectively, 87.6% and 90.6%. CT performed least well in the diagnosis of costochondritis, with a sensitivity of 87.6% and specificity of only 56.9%. CT sinography added additional useful information.
COMMENT BY STAN DERESINSKI, MD, FACP
Poststernotomy infections are a common complication of cardiovascular surgery, occurring in 81 (2.2%) of 3711 patients in one series.1 Risk factors include obesity, diabetes mellitus, associated saphenous vein donor site infection, repeat sternotomy because of bleeding, and the need for three or more units of blood.2,3
Posternotomy infections may involve a number of distinct anatomic sites, each having implications for the appropriate surgical approach. As Gur et al indicate, the resultant infections can be classified as presternal soft tissue infection, a sinus tract to a foreign body, involvement of the external sternal plate or a sinus tract to the sternal medullary cavity, internal sternal plate involvement, costochondritis, and mediastinitis.
Most cases of poststernotomy wound infections are readily apparent to the clinician, with findings that include the usual manifestations of wound infection, as well as sternal tenderness and instability. Gas bubbles may rarely be seen emanating from the sternal wound. In some cases, the wound may appear intact and the first evidence of deep infection may be fever or bacteremia. Of 25 patients at one center with fever higher than 38.5°C after cardiac surgery, nine had bacterial infections and three of these were cases of mediastinitis.4
Misawa and colleagues previously reported CT findings in 11 patients with mediastinitis after cardiac surgery.5 Mediastinal soft tissue swelling was seen in seven patients, bilateral pleural effusion in nine, sternal dehiscence or sternal erosion in eight, and subcutaneous fluid accumulation was found in seven patients with mediastinitis. However, bilateral pleural effusion and mediastinal swelling were each also noted in one of 10 post-cardiac surgery controls who did not have mediastinitis. CT appears to be useful diagnostically and allows localization of the infection, allowing the surgeon to plan the appropriate surgical approach. However, as found by Misawa et al, normal postoperative changes may confuse interpretation.6 In contrast to CT, routine chest radiography is rarely diagnostically useful. The value of magnetic resonance imaging is uncertain and is often not possible because of the presence of ferromagnetic metals in the patient. 111-Indium-labeled leukocyte scanning has been reported to be useful, but this also requires further investigation.7
Culture of intraoperatively placed epicardial pacing wires has been suggested to be a useful procedure in the diagnosis of mediastinitis. Maroto and colleagues in Madrid have reported that a negative culture of epicardial pacing wires removed 7-9 days after surgery is strong evidence of mediastinitis, with a negative predictive value of 99.1%.8 In the United States, these wires are ordinarily removed much earlier; the value of a negative culture obtained at this earlier time is uncertain. Needle aspiration of the mediastinum by a substernal approach has been advocated as a useful diagnostic technique, detecting organisms in approximately two-thirds of patients with mediastinitis.9 However, the overall diagnostic value of this procedure remains uncertain.
Management of poststernotomy infections involves appropriate antimicrobial therapy and aggressive surgical intervention. The general surgical approach depends, of course, on the level and site of infection. (See Table.) Infection limited to the presternal tissues requires only local debridement. On the other hand, a controversy continues over the use of early or late closure and use of flaps in patients with deep infection. A retrospective comparison of sternal debridement with primary closure and of sternectomy with flap reconstruction found comparable results.10 In general, it appears that early mediastinitis can be managed with debridement and mediastinal irrigation, while late disease is more likely to require radical debridement and muscle flap or omental flap closure.11-13
| Table | |||
| Radiological Classification and Recommended Treatment/ Reconstructive Methods in Sternal Wound Infection | |||
| Stage | Radiological Interpretation | Treatment | Reconstruction |
| I | Presternal soft-tissue infection | Soft-tissue debridement or conservative treatment | Primary closure or secondary healing or local skin/muscle flap |
| II | Sinus tract to foreign body | Sinusectomy and foreign body removal | Primary closure, secondary healing, or local skin/muscle flap |
| III | External plate involvement or sinus to sternal medulla | Resection of sternal external plate | Bilateral PM advancement or unilateral PM/RA turnover or their combination |
| IVa* | Internal plate involvement or paramedian incision with signs of infection | Total or semitotal sternectomy | Bilat PM advancement, unilateral PM or RA turnover, omentum flap, or their combination |
| IVb | Costochondral infection | Resection of ribs or clavicle | Primary closure or PM local flap |
| V | Mediastinal infection | Debridement and irrigation | PM, RA, or omentum flap or their combination |
| * In stage IVa, semitotal sternectomy denotes the resection of the smaller hemisternum resulting from the paramedian incision. PM, pectoralis major muscle; RA, rectus abdominis muscle. | |||
| Table reprinted with permission from Gur E, et al. Plast Reconst Surg 1998;101:348-355. | |||
References
1. Munoz P, et al. Clin Infect Dis 1997;25:1060-1064.
2. El Oakley R, et al. J Cardiovasc Surg (Torino) 1997;38: 595-600.
3. Borger MA, et al. Ann Thorac Surg 1998;65: 1050-1056.
4. Ishikawa S, et al. J Cardiovasc Surg (Torino) 1998;39: 95-97.
5. Misawa Y, et al. Ann Thorac Surg 1998;65:622-624.
6. Carrol CL, et al. J Comput Assist Tomogr 1987;11: 449-454.
7. Browdie DA, et al. Ann Thorac Surg 1991;51:290-229.
8. Maroto LC, et al. Clin Infect Dis 1997;24:419-421.
9. Grossi EU, et al. Ann Thorac Surg 1985;40:214-223.
10. Borger MA, et al. Ann Thorac Surg 1998;65: 1050-1056.
11. Satta J, et al. Scand Cardiovasc J 1998;32:29-32.
12. Yasuura K, et al. Ann Surg 1998;227:455-459.
13. El Gamel A, et al. Ann Thorac Surg 1998;65:41-46.
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