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Ann Thorac Surg 1998;65:622-624
© 1998 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Infectious Mediastinitis After Cardiac Operations: Computed Tomographic Findings

Department of Thoracic and Cardiovascular Surgery, Jichi Medical School, Tochigi, Japan

Accepted for publication August 21, 1997.

Dr Misawa, Department of Thoracic and Cardiovascular Surgery, Jichi Medical School, Yakushiji 3311-1, Minami-Kawachi, Tochigi, 329-04, Japan.

	Abstract

Top Abstract Introduction Material and Methods Results Comment References

 
Background. Infectious mediastinitis after cardiac operations is of great concern to cardiac surgeons because of its poor prognosis. Prompt surgical interventions such as debridement and irrigation are the key to treatment of infectious mediastinitis.

Methods. We surveyed retrospectively the cases of 722 consecutive cardiac surgery patients at our hospital. Mediastinitis developed in 21 patients after the cardiac operation. We performed computed tomography in 11 of these patients before resternotomy and in 10 patients as the control 2 to 3 weeks after the cardiac operation.

Results. Mediastinal soft tissue swelling was seen in 7 patients, bilateral pleural effusion was found in 9 patients, sternal dehiscence or sternal erosion was observed in 8 patients, and subcutaneous fluid accumulation was found in 7 of the mediastinitis group. Unilateral pleural effusion was seen in 6 and bilateral effusion in 1, and mediastinal soft tissue swelling was seen in 1 patient of the control group.

Conclusions. Our study showed that mediastinal soft tissue mass combined with bilateral pleural effusion can be a characteristic computed tomography finding in post-sternotomy infectious mediastinitis, and that chest computed tomography is more sensitive to detecting sternal dehiscence, sternal erosion, and subcutaneous fluid accumulation.

	Introduction

Top Abstract Introduction Material and Methods Results Comment References

 
Infectious mediastinitis after cardiac operation is of great concern to cardiac surgeons because of its poor prognosis [1]; it is also difficult to treat. Diagnostic procedures for postoperative mediastinitis often include physical examination, chest roentgenography, and computed tomography (CT). Chest CT findings after sternotomy include aseptic hematoma or fluid collection in the mediastinum [2]. It is not always easy to differentiate these from abscess formation in the mediastinum. Redness of the skin wound, sternal dehiscence, and subcutaneous abscess formation are observed in an advanced case. Prompt surgical interventions such as debridement and irrigation are the key to treatment of infectious mediastinitis. It was our intention to identify specific CT findings in postoperative mediastinitis to get a definite diagnosis.

	Material and Methods

Top Abstract Introduction Material and Methods Results Comment References

 
Seven hundred twenty-two consecutive patients, who had cardiac surgical procedures with extracorporeal circulation between 1990 and 1996, were included in this study. Mediastinitis developed after the cardiac operation in 21 of these patients (2.9%). There were 5 patients with ischemic heart disease, 2 with Stanford type A aortic dissection, 1 with valvular disease, 1 with atrial septal defect, and 1 with invasive hepatoma in the right atrium. All patients had undergone cardiopulmonary bypass through a median sternotomy. We performed CT in 11 of these patients before resternotomy and also in 10 patients without any signs of mediastinitis 2 to 3 weeks after cardiac operation through median sternotomy. Computed tomography findings were reviewed retrospectively. The factors considered were pleural effusion, soft tissue swelling in the mediastinum, oval or round mass in the mediastinum, sternal dehiscence, and subcutaneous mass observed in CT. Pleural effusion with any amount detected in CT was considered as a positive finding. An oval or round mass was seen as a convex, high-density area that shows its expanding process (Fig 1) in contrast to any mass with an irregular contour, a concave, high-density area without an expanding process (Fig 2). Soft tissue swelling in the mediastinum was defined by a convex, low-density area of 3 cm or more in length (Fig 3); three slices or more in CT scan. Sternal dehiscence was seen as a loosening and malalignment of the sutured sternum. A subcutaneous mass was defined as a high-density area indicating subcutaneous abscess formation with direct communication to substernal masses (Fig 4). Pleural effusion was categorized into three subgroups: no effusion, unilateral effusion, and bilateral (Table 1). We compared the CT findings in these patients with postoperative infectious mediastinitis with those of the control patients.

View larger version (129K): [in this window] [in a new window]   A typical computed tomographic finding of oval or round mass. Arrows show a convex, high-density area in the mediastinum.

View larger version (107K): [in this window] [in a new window]   A computed tomographic finding of a patients without any inflammatory signs and symptoms. Arrows show a concave, high-density area with an irregular contour.

View larger version (129K): [in this window] [in a new window]   A typical soft tissue swelling seen in a patient with infectious mediastinitis. A convex, low-density area (arrows), which was 3 cm or more in length, was recognized in a patient with mediastinitis.

View larger version (125K): [in this window] [in a new window]   A subcutaneous mass was defined as a high-density area indicating subcutaneous abscess formation (arrows) with direct communication to substernal masses.

	Results

Top Abstract Introduction Material and Methods Results Comment References

Table 1 shows the CT findings of each group. Bilateral pleural effusion and mediastinal soft tissue swelling were predominantly seen in the mediastinitis group. In the control group, no pleural effusion was recognized in 3 patients, unilateral pleural effusion in 6, and bilateral effusion in 1. An oval or round mass was seen in both groups. Sternal dehiscence, sternal erosion, and subcutaneous fluid accumulation were observed in the mediastinitis group alone. Neither physical examination nor chest roentgenography was able to reveal sternal dehiscence or sternal erosion in 3 of the 8 patients. In addition, 7 patients showed subcutaneous fluid accumulation in the mediastinitis group, but no one showed such a mass in the control group. In 3 of the 7 patients, physical examination failed to reveal it.

The 10 patients with mediastinitis underwent resternotomy for debridement and irrigation with 10 to 20 L of physiologic saline solution, after omental flap transfer with or without subsequent continuous mediastinal irrigation [3]. Operative findings endorsed the diagnosis of infectious mediastinitis.

Microbiologic examination of the materials collected from the mediastinum revealed Methicillin-resistant Staphylococcus aureus in 4 patients, methicillin-sensitive Staphylococcus aureus in 3, Pseudomonas aeruginosa in 2, and Alcaligenes xylosoxidans in 1. In 1 patient, no organism was detected; clinical and operative findings were compatible with infectious mediastinitis. Three patients fully recovered and were discharged, 1 patient is recovering but still in hospital, 6 patients could not overcome their intractable mediastinitis and died of sepsis or multiple organ failure 10 days to 6 months after resternotomy, and 1 patient perished after rupture of a descending aortic aneurysm 4 days after drainage for mediastinitis.

	Comment

Top Abstract Introduction Material and Methods Results Comment References

 
The mediastinum has no mesothelium except inside the pericardium. Thus, conservative treatment for infectious mediastinitis after a cardiac operation tends to fail because of immunologic difficulties. Prompt surgical interventions such as debridement and irrigation are recommended for the treatment of infectious mediastinitis. However, the mediastinitis is often quite advanced before surgeons recognize it when they reexplore the mediastinum.

In this study, mediastinitis was diagnosed mainly on the basis of physical examination and other clinical data. The chest CT was ordered for additional information. Chest roentgenogram might show pleural effusion, widened mediastinum, or sternal dihescence in cases of advanced mediastinitis [4]. Some investigators have reported that diagnostic chest CT in diagnostic procedures did not contribute to clinical results [5], but anecdotal case reports have shown its usefulness [3][6]. Laboratory data might contribute to early prediction of poststernotomy mediastinitis [7][8].

In our study, poststernotomy mediastinitis occurred 2 weeks or more after operation; noninfected hematoma, fluid collection, or pleural effusion also can exist at this stage. Therefore, it is not easy to differentiate these masses from abscess formation. Bilateral pleural effusion was predominantly seen in the mediastinitis group. The contours of mediastinal masses did not show characteristic features for mediastinitis; some had oval or round contours, and others were jagged. Thus, we do not think fluid collection without any other findings implicates mediastinitis. We defined convex, soft tissue masses of 3 cm or more in length as a mass that might reveal an inflammatory process in the thymus or adipose tissue around the pericardium and mediastinal pleura. Only 1 patient in the control group showed such a swelling mass without pleural effusion, but his clinical course did not implicate mediastinitis at all. Thus, mediastinal soft tissue swelling combined with bilateral pleural effusion can be a characteristic finding of infectious mediastinitis. In other words, no patient showing mediastinal soft tissue swelling combined with bilateral pleural effusion was recognized in the control group.

In 3 of the 8 patients, neither physical examination nor chest roentgenography was able to reveal sternal dehiscence or sternal erosion shown in chest CT. In 3 patients, physical examination also failed to reveal subcutaneous masses with direct communication to substernal masses detected in chest CT. Further prospective studies are mandatory to clarify the relationship between these findings and poststernotomy mediastinitis.

Finally, 4 patients had mediastinitis caused by a highly intractable organism, methicillin-resistant Staphylococcus aureus, and this may have been a cause of high mortality rate in this study. At resternotomy in mediastinitis, we do prefer omental transfer to muscle flap transfer because the omentum has not only mass effect filling the dead space but also unique properties such as the enhancement of neovascularization and the ability to absorb exudate [6].

In conclusion, mediastinal soft tissue mass combined with bilateral pleural effusion can be a characteristic CT finding of post-sternotomy mediastinitis. Mediastinal masses composed of hematoma or fluid accumulation were not characteristic findings for post-sternotomy mediastinitis. Chest CT was more sensitive in detecting sternal dehiscence, sternal erosion, and subcutaneous fluid accumulation.

	References

Top Abstract Introduction Material and Methods Results Comment References

 

1. Sarr MG, Gott VL, Townsend TR Mediastinal infection after cardiac surgery. Ann Thorac Surg 1984;39:415-423.
2. Rosenbaum GS, Klein NC, Gunha BA Poststernotomy mediastinitis. Heart Lung 1990;19:371-372.[Medline]
3. Oyama H, Misawa Y, Hasagawa N, Kato M, Hasegawa T, Fuse K A successful treatment of infective mediastinitis with chylomediastinum after the closure of atrial septal defect. Kyobugeka 1994;47:864-865.
4. Voiriot P, Marcoux JA, Duperval R, Teijeira J Staphylococcus aureus mediastinitis: prognostic usefulness of an early medicosurgical therapy. Infect Control 1987;8:325-328.[Medline]
5. Breatnach E, Nath PH, Delany DJ The role of computed tomography in acute and subacute mediastinitis. Clin Radiol 1986;37:139-145.[Medline]
6. Omura K, Misaki T, Takahashi, Kobayashi K, Watanabe Y Omental transfer for the treatment of sternal infection after cardiac surgery: report of three cases. Jpn J Surg 1994;24:67-71.
7. Miholic J, Hudec M, Muller MM, Domanig E, Wolner E Early prediction of deep sternal wound infection after heart operations by alpha-1 acid glycoprotein and C-reactive protein measurement. Ann Thorac Surg 1986;42:429-433.[Abstract]
8. Verkkala K, Valtonen V, Jarvinen A, Tolppanen EM Fever, leucocytosis and C-reactive protein after open-heart surgery and their value in the diagnosis of postoperative infections. Thorac Cardiovasc Surgeon 1987;35:78-82.[Medline]

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Yoshio Misawa Katsuo Fuse Tsuguo Hasegawa Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Misawa, Y. Articles by Hasegawa, T. Search for Related Content PubMed PubMed Citation Articles by Misawa, Y. Articles by Hasegawa, T.