Infectious mediastinitis after cardiovascular surgery: role of computed tomography

Computed Tomography Scanning for Sternal Wound Infections: A Systematic Review

Background

Sternal wound infection (SWI) has always been a significant risk in patients who undergo sternotomies as part of their cardiac surgical procedures. Computed tomography (CT) imaging is often used to diagnose and assess sternal wound infections. Its purpose includes identifying and locating infection and any sternal dehiscence.

Methods

A systematic literature review across PubMed, Embase, and Ovid was performed according to PRISMA guidelines to identify relevant articles that discussed the utility of CT scanning for SWI, common features identified, patient outcomes and sensitivity/specificity (Figure 1).

Results

25 papers were included. 100% (n=25) of the papers were published in peer-reviewed journals. CT scans in SWIs can be seen as a beneficial aid in diagnosing as well as determining the components of infection. Commonalities were identified such as fluid collection in the mediastinum, free gas, pleural effusions, and sternal dehiscence which point towards the presence of sternal wound infection.

Conclusion

CT scanning is a novel and emerging methodology for imaging in SWI and post-sternotomy complications, hence increased research is required to expand the literature on this area as well as the creation of guidelines and cut-offs or signs for radiology professionals to identify and determine the extent of infection.

18F-FDG/PET-CT imaging findings after sternotomy

BACKGROUND

The clinical diagnosis of deep sternal wound infection (DSWI) is supported by imaging findings including 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT). To avoid misinterpretation due to normal post-surgery inflammation we assessed normal imaging findings in non-infected patients after sternotomy.

METHODS

This is a prospective cohort study including non-infectious patients with sternotomy. All patients underwent 18F-FDG-PET/CT at either 5 weeks (group 1), 12 weeks (group 2) or 52 weeks (group 3) post-surgery. 18F-FDG uptake was scored visually in five categories and assessed quantitatively.

RESULTS

A total of 44 patients were included. Sternal mean SUVmax was 7.34 (± 1.86), 5.22 (± 2.55) and 3.20 (± 1.80) in group 1, 2 and 3, respectively (p < 0.01). Sternal mean SUVmean was 3.84 (± 1.00), 2.69 (± 1.32) and 1.71 (± 0.98) in group 1, 2 and 3 (p < 0.01). All patients in group 1 had elevated uptake whereas group 2 and 3 showed 2/15 (13%) and 11/20 (55%) patients respectively with no elevated uptake. Group 3 still showed an elevated uptake pattern in in 9/20 (45%) and in 3/9 (33%) with a high-grade diffuse uptake pattern.

CONCLUSION

This study shows significant lower sternal 18F-FDG at 55 weeks compared to 5 weeks post-sternotomy however elevated uptake patterns may persist.

Role of ultrasound in the treatment of pediatric infectious diseases: case series and narrative review

BACKGROUND

Infectious diseases are common in pediatric patients. In these patients, ultrasound is a useful imaging modality that involves no irradiation or sedation and can be performed repeatedly at the patient's bedside. The purpose of this review was to show pediatric cases with infectious disease that used ultrasound to decide the methods of treatment.

DATA SOURCES

Literature review was performed using Pubmed as the medical database source. No year-of-publication restriction was placed. The mesh terms used were: "ultrasound", "sonography", "infectious disease", "treatment", "antibiotics", "surgical intervention", "pediatric", "children", "deep neck abscess", "pyothorax", "empyema", "pneumonia", "urinary tract infection", "intra-abdominal abscess", "soft tissue infection", "septic arthritis", "osteomyelitis", and "surgical site infection".

RESULTS

We presented pediatric case series with infectious diseases, including deep neck abscess, pyothorax and empyema, pneumonia, urinary tract infection, intra-abdominal abscess, soft tissue infection, septic arthritis and osteomyelitis, and surgical-site infection. Ultrasound was useful for evaluating the extent and location of inflammation and abscess and for decision-making concerning surgical intervention.

CONCLUSION

Knowledge of these sonographic findings is important for sonographers during examinations and for physicians when determining the treatment plan and period of antibiotic therapy for infected lesions.

Surgical Site Infection in Cardiac Surgery

Surgical site infections (SSIs) are one of the most significant complications in surgical patients and are strongly associated with poorer prognosis. Due to their aggressive character, cardiac surgical procedures carry a particular high risk of postoperative infection, with infection incidence rates ranging from a reported 3.5% and 26.8% in cardiac surgery patients. Given the specific nature of cardiac surgical procedures, sternal wound and graft harvesting site infections are the most common SSIs. Undoubtedly, DSWIs, including mediastinitis, in cardiac surgery patients remain a significant clinical problem as they are associated with increased hospital stay, substantial medical costs and high mortality, ranging from 3% to 20%. In SSI prevention, it is important to implement procedures reducing preoperative risk factors, such as: obesity, hypoalbuminemia, abnormal glucose levels, smoking and S. aureus carriage. For decolonisation of S. aureus carriers prior to cardiac surgery, it is recommended to administer nasal mupirocin, together with baths using chlorhexidine-based agents. Perioperative management also involves antibiotic prophylaxis, surgical site preparation, topical antibiotic administration and the maintenance of normal glucose levels. SSI treatment involves surgical intervention, NPWT application and antibiotic therapy.

Multimodality imaging of Surgicel®, an important mimic of post-operative complication in the thorax

Absorbable hemostatic agents such as Surgicel are hemostatic materials composed of an oxidized cellulose polymer used to control post-surgical bleeding and cause coagulation. This material is sometimes purposefully left in situ where it slowly degrades over time and can produce an imaging appearance that mimics serious post-operative complications such as gangrenous infections and anastomotic leaks as well as potentially mimicking disease recurrence in later stages. In this article, we review the multimodality imaging appearance of this material in situ longitudinally in the range of post-operative settings, in order to promote awareness of this entity when interpreting post-operative imaging. We present this as a pictorial review focusing primarily but not exclusively on the chest noting that the thoracic imaging appearance of Surgicel^® is less well reported in the published literature. An understanding of this entity may help to minimize erroneous diagnosis of a postoperative complication leading to unnecessary interventions.

Prevention, Diagnosis and Management of Post-Surgical Mediastinitis in Adults Consensus Guidelines of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES)

This is a consensus document of the Spanish Society of Cardiovascular Infections (SEICAV), the Spanish Society of Thoracic and Cardiovascular Surgery (SECTCV) and the Biomedical Research Centre Network for Respiratory Diseases (CIBERES). These three entities have brought together a multidisciplinary group of experts that includes anaesthesiologists, cardiac and cardiothoracic surgeons, clinical microbiologists, infectious diseases and intensive care specialists, internal medicine doctors and radiologists. Despite the clinical and economic consequences of sternal wound infections, to date, there are no specific guidelines for the prevention, diagnosis and management of mediastinitis based on a multidisciplinary consensus. The purpose of the present document is to provide evidence-based guidance on the most effective diagnosis and management of patients who have experienced or are at risk of developing a post-surgical mediastinitis infection in order to optimise patient outcomes and the process of care. The intended users of the document are health care providers who help patients make decisions regarding their treatment, aiming to optimise the benefits and minimise any harm as well as the workload.

Computed tomography findings of mediastinitis after cardiovascular surgery

BACKGROUND

To our knowledge, no systematic study has been conducted on computed tomography (CT) imaging of mediastinitis in children post-cardiovascular surgery. We aimed to assess the CT findings of pediatric patients diagnosed with mediastinitis after cardiovascular surgery.

METHODS

We included 28 pediatric patients with suspected mediastinitis after undergoing cardiovascular surgery and who underwent CT. Patients were divided into a group with mediastinitis requiring antibiotic therapy (n = 15) confirmed by positive bacterial culture from the mediastinum and a group without mediastinitis (n = 13). Fisher's exact test was used to compare the following CT findings between the two groups: (i) mediastinal fluid collection; (ii) free gas bubble within fluid collection; (iii) sternal destruction; and (iv) capsular ring enhancement. The enhancement extent was categorized into the following four grades: whole rim enhancement, >50% of the rim enhancement, <50% of the rim enhancement, and no rim enhancement. A receiver operating characteristic curve analysis was performed to establish a cut-off point for obtaining the maximum diagnostic accuracy.

RESULTS

A significant difference was observed between patients, with and without mediastinitis in sternal destruction (73.6% vs 0%, P = <0.0001) and capsular ring enhancement (100.0% vs 38.5%, P = 0.0004). By using a cut-off grade of the whole rim enhancement, the estimated sensitivity and specificity for mediastinitis diagnosis were 100% and 92.3%, respectively.

CONCLUSION

Computed tomography findings of sternal destruction and capsular ring enhancement were observed more in patients with mediastinitis than in those without mediastinitis, and should be assessed carefully to diagnose mediastinitis accurately in pediatric patients who have undergone cardiac surgery.

Surgicel® packing remnants mimicking mediastinitis after adult cardiac surgery

Surgicel® is one of the most commonly used bioabsorbable topical haemostatic agents. Some articles have reported that Surgicel® remnants might be misdiagnosed as an abscess. However, the number of reports in the cardiothoracic surgical field is limited. Herein, we report a 65-year-old woman who was suspected of having mediastinitis on computed tomography after redo-Bentall operation. Reoperation revealed that internal accumulation of Surgicel® remnants mimicked mediastinitis. It is important to share the use and location of Surgicel® with radiologists. If mediastinitis cannot be ruled out, the next step of reoperation or magnetic resonance imaging should be promptly taken.

Computed tomography improves the differentiation of infectious mediastinitis from normal postoperative changes after sternotomy in cardiac surgery

OBJECTIVES

To identify CT parameters independently associated with infectious mediastinitis after cardiac surgery and to improve the discrimination of patients with acute infection from those with normal postoperative changes.

METHODS

In this single-center, retrospective, observational cohort study, we evaluated thoracic CT scans of poststernotomy cardiac surgery patients. Inclusion criteria were clinically suspected mediastinitis, unclear CT signs (e.g., retrosternal mass), and subsequent deep revision surgery. Revision surgery and microbiological samples determined the mediastinitis status. Overall, 22 qualitative and quantitative CT imaging parameters were assessed and associated with infectious mediastinitis in univariate and multivariate regression models. Discriminative capacity and incremental value of the CT features to available clinical parameters were determined by AUC and likelihood-ratio tests, respectively.

RESULTS

Overall 105 patients (82% men; 67.0 ± 10.3 years) underwent CT and deep revision surgery. Mediastinitis was confirmed in 83/105 (79%) patients. Among available clinical parameters, only C-reactive protein (CRP) was independently associated with infectious mediastinitis (multivariate odds ratio (OR) (per standard deviation) = 2.3; p < 0.001). In the CT, the presence of free gas, pleural effusions, and brachiocephalic lymph node size were independently associated with mediastinitis (multivariate ORs = 1.3-6.3; p < 0.001-0.039). Addition of these CT parameters to CRP increased the model fit significantly (X² = 17.9; p < 0.001; AUC, 0.83 vs. 0.73).

CONCLUSION

The presence of free gas, pleural effusions, and brachiocephalic lymph node size in CT is independently associated with infectious mediastinitis in poststernotomy patients with retrosternal mass. These imaging features may help to differentiate mediastinitis from normal postoperative changes beyond traditional clinical parameters such as CRP.

KEY POINTS

• Presence of free gas, pleural effusions, and brachiocephalic lymph node size on CT are associated independently with infectious mediastinitis. • Combination of these CT parameters increases the discriminatory capacity of clinical parameters such as CRP.

Defining post-sternotomy mediastinitis for clinical evidence-based studies

Background

Considerable advances have already been made in the treatment of deep thoracic wound infections following a median sternotomy for cardiac surgery. Further improvement in diagnosis, treatment, and outcome will require a targeted approach by multidisciplinary teams. Clear communication and synergy between the various clinical and supportive disciplines would assist in removing the last barriers to standardized evidence-based studies and the development of improved evidence-based guidelines.

Methods

An extensive literature search without language restrictions was carried out on PubMed (Medline), EMBASE, and Web of Science, covering the period 1988 to week 16, 2014, and a manual search of the reference lists was performed regarding all possible definitions and classifications of post-sternotomy mediastinitis. Two hundred and eighteen papers describing post-sternotomy infections in a multitude of terms were identified, and the strengths and weaknesses of the most popular definitions and terms relating specifically to post-sternotomy infections were examined.

Results

This study revealed that clinicians use a multitude of terms to describe post-sternotomy infections without defining the condition under treatment. Occasionally, older epidemiological (surveillance) definitions were used. It also shows that supportive disciplines have their own definitions, or interpretations of existing definitions, to describe these infections.

Conclusion

The outcome of this study is that clinicians have adopted no single definition, which is essential for further improvement for evidence-based studies. We suggest that it is possible to adopt a single term for thoracic infection after a sternotomy (and only sternotomy), and propose a clinical definition for this purpose.

Evaluation of fever and infections in cardiac surgery patients

Fever following cardiac surgery is common and may be infectious or noninfectious in etiology. In this article, we review the major causes of postoperative fever while highlighting special considerations in cardiac surgery patients. We also outline a structured approach to evaluation and present an overview of diagnostic and management considerations for mediastinitis, postpericardiotomy syndrome, prosthetic valve endocarditis, aortic vascular graft infections, and ventricular assist device infections.

Volumetric Computed Tomography Angiography in the Evaluation of Mediastinal Fluid Collections following Congenital Cardiac Surgery

We present 3 patients with 4 causes of mediastinal fluid collection after congenital cardiac surgery in this extended case report. Volumetric computed tomography played an essential role in diagnosing causes and extent, relevant to subsequent management. Recent advances in volumetric computed tomography allow fast and accurate imaging of cardiovascular and extravascular structures in children with acceptable radiation dose, providing a powerful imaging tool for the evaluation of complications after congenital cardiac surgery.

Magnetic resonance imaging of soft tissue infection with iron oxide labeled granulocytes in a rat model

OBJECT

We sought to detect an acute soft tissue infection in rats by magnetic resonance imaging (MRI) using granulocytes, previously labeled with superparamagnetic particles of iron oxide (SPIO).

MATERIALS AND METHODS

Parasternal infection was induced by subcutaneous inoculation of Staphylococcus aureus suspension in rats. Granulocytes isolated from isogenic donor rats were labeled with SPIO. Infected rats were imaged by MRI before, 6 and 12 hours after intravenous injection of SPIO-labeled or unlabeled granulocytes. MR findings were correlated with histological analysis by Prussian blue staining and with re-isolated SPIO-labeled granulocytes from the infectious area by magnetic cell separation.

RESULTS

Susceptibility effects were present in infected sites on post-contrast T2*-weighted MR images in all animals of the experimental group. Regions of decreased signal intensity (SI) in MRI were detected at 6 hours after granulocyte administration and were more pronounced at 12 hours. SPIO-labeled granulocytes were identified by Prussian blue staining in the infected tissue and could be successfully re-isolated from the infected area by magnetic cell separation.

CONCLUSION

The application of SPIO-labeled granulocytes in MRI offers new perspectives in diagnostic specificity and sensitifity to detect early infectious processes.