PET-CT imaging in patients with chronic sternal wound infections prior to reconstructive surgery: A case series

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.

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.

Gram-negative bacteria as a cause of mediastinitis after cardiac surgery

PURPOSE OF REVIEW

Poststernotomy mediastinitis (PSM) remains a serious infection and is significantly associated with high morbidity, short-term and long-term mortality. Gram-negative bacteria (GNB) are an underestimated cause of PSM, and there is little information on the risk factors, prevention, diagnosis and management of GNB PSM.

RECENT FINDINGS

The pathogenesis of PSM is the result of a complex and multifactorial interplay between intraoperative wound contamination, host-related and surgical host factors but GNB are probably mostly translocated from other host site infections. GNB are frequent cause of PSM (18-38% of cases) and GNB PSM have shown to more frequently polymicrobial (20-44%). GNG PSM has shown to occur earlier than Gram-positive PSM. Early diagnosis is crucial to successful treatment. The management of PSM needs a combination of culture-directed antimicrobial therapy and an early extensive surgical debridement with either immediate or delayed closure of the sternal space. Antibiotic treatment choice and duration should be based on clinical evaluation, evolution of inflammatory markers, microbiological tests and imaging studies. Mortality has shown to be significantly higher with GNB PSM compared with other causes and the inappropriateness of initial antibiotic therapy may explain the worse outcome of GNB PSM.

SUMMARY

GNB PSM is usually undervalued in the setting of PSM and have shown to be a frequent cause of inappropriate treatment with adverse prognostic potential. There is a need for efforts to improve knowledge to prevent and adequately treat GNB PSM.

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.

Utility of FDG-PET/CT for the Detection and Characterization of Sternal Wound Infection Following Sternotomy

Purpose

FDG-PET/CT has the potential to play an important role in the diagnosis of sternal wound infections (SWI). The purpose of this study was to analyze the diagnostic accuracy of FDG-PET/CT for SWI in patients following sternotomy.

Methods

We performed a single-center, retrospective analysis of patients who had undergone median sternotomy and FDG-PET/CT imaging. The gold standard consisted of positive bacterial culture and/or the presence of purulent material at surgery. Qualitative patterns of sternal FDG uptake, SUV_max, and associated CT findings were determined, and an imaging scoring system was developed. The diagnostic performances were studied in both the recent (≤ 6 months between sternotomy and imaging) and remote surgery phase (> 6 months).

Results

A total of 40 subjects were identified with 11 confirmed SWI cases. Consensus interpretation was associated with a sensitivity of 91% and specificity of 97%. Combination of uptake patterns yielded an AUC of 0.96 while use of SUVmax yielded an AUC of 0.82.

Conclusions

Results suggest that FDG-PET/CT may be useful for the diagnosis of SWI with optimal diagnostic accuracy achieved by identifying specific patterns of uptake. SUV_max can be helpful in assessing subjects with remote surgery, but its use is limited in the context of recent surgery. Further studies are required to confirm these results.

Current perspectives on diagnosis and management of sternal wound infections

Deep sternal wound infection (DSWI), also known as mediastinitis, is a serious and potentially fatal condition. The diagnosis and treatment of DSWI are challenging. In this current narrative review, the epidemiology, risk factors, diagnosis, and surgical and antimicrobial management of DSWI are discussed. Ideally, the management of DSWI requires early and sufficient surgical debridement and appropriate antibiotic therapy. When foreign material is present, biofilm-active antibiotic therapy is also needed. Because DSWI is often complex, the management requires the involvement of a multidisciplinary team consisting of cardiothoracic surgeons, plastic surgeons, intensivists, infectious disease specialists, and clinical microbiologists.