Mediastinitis by definition refers to inflammation of the connective tissues and fat within the mediastinum.
In clinical practice; mediastinitis is generally used to refer to acute mediastinitis, resulting from bacterial infection within the mediastinum. This is considered a serious and potentially life-threatening condition. Chronic mediastinitis (fibrosing mediastinitis) is a condition with a varied etiology which includes; idiopathic, immune-mediated, or infective (e.g. tuberculosis).
Acute mediastinitis is usually a result of the spread of infection from an adjacent source .
- esophageal perforation
- this may also occur due to anastamotic dehissence post esophageal surgery
- deep sternal wound infection
- post-operative infection after median sternotomy
- descending necrotizing mediastinitis
- spread from an odontogenic or oropharyngeal infection
- less common causes
- extension of infection from the lung or extension of adjacent osteomyelitis (e.g sternoclavicular joint)
Acute mediastinitis is uncommon, and is associated with high morbidity and considerable mortality. Infection secondary to median sternotomy has been reported to have a prevalence of 0.5-5% . Risk factors for mediastinitis include diabetes mellitus and immunosuppression, in addition to factors which could contribute to increased postoperative complications, such as advanced age, obesity and smoking .
Patients may experience retrosternal pain and exhibit systemic signs such as fever, tachycardia or hypotension. Blood results may reveal a raised WCC, neutrophilia and CRP .
Additional symptoms and signs depend upon the etiology and specific clinical scenario.
Mediastinitis secondary to esophageal perforation may present after a recent endoscopy, or after a bout of forceful vomiting (Boerhaave syndrome). Patients with a mediastinal infection secondary to an infected median sternotomy wound may have signs of wound infection on examination . Infection spreading from the head and neck may have additional signs pointing to a localized source of infection such as dental, neck or throat pain.
Findings are non-specific and overlap with other pathologies involving the mediastinum. Findings may include mediastinal widening and abnormality of the right paratracheal stripe. Additional features which could indicate esophageal perforation in the correct clinical context include pneumomediastinum and subcutaneous emphysema. Pleural effusions may also be seen .
Features may include:
- evidence of mediastinal inflammation such as fat stranding, edema and loss of the normal fat planes
- single or multiple mediastinal fluid collections which may contain gas locules and demonstrate an enhancing wall
- locoregional lymphadenopathy
- complications from spread of infection: empyema or subphrenic abscess. Pericardial effusion may indicate pericarditis
It is important to note that a level of inflammatory change, fluid and hemorrhage is expected following recent cardiac surgery and may last up to 2 weeks . A combination of, comparison to previous imaging, judgment of expected appearance, and discussion with the clinical team regarding the patients' current condition may be helpful in guiding interpretation.
Additional findings depend on the etiology:
- ossophageal perforation: thickening and/or collection adjacent to the affected portion of the esophagus, extravasation of oral contrast into the mediastinum (if oral contrast administered)
- deep sternal wound infection: associated subcutaneous stranding/collection may be evident
- descending necrotizing mediastinitis: imaging of the neck may reveal the infection extending through the neck spaces into the mediastinum
Treatment and prognosis
Acute mediastinitis is a serious and potentially life-threatening condition with considerable mortality. Early diagnosis, antibiotic therapy and surgical drainage are essential in the control of infection . Image-guided drainage could be considered in specific instances. Microbiological analysis of fluid samples is important in guiding further antibiotic therapy. Further management will depend on the underlying specific cause of infection .