Acute mediastinitis is an acute bacterial infection of mediastinal tissues and is a life-threatening emergency. Most commonly results from esophageal perforation (Boerhaave syndrome, endoscopic/surgical perforation, foreign body), post-sternotomy infection, and caudal spread of oropharyngeal/cervical infections (descending necrotizing mediastinitis). On CT, obliteration of mediastinal fat planes, fluid collections, pneumomediastinum (free air), air-fluid levels, and thickening of surrounding tissues are pathognomonic. Mortality reaches 40-60% without treatment; early diagnosis and emergent surgical drainage are life-saving.
Age Range
30-70
Peak Age
50
Gender
Equal
Prevalence
Rare
Acute mediastinitis is a polymicrobial bacterial infection of mediastinal tissues. In esophageal perforation, leakage of saliva and food particles contaminated with gastric acid into the mediastinum triggers rapid bacterial proliferation — anaerobes (Bacteroides, Peptostreptococcus), aerobes (Streptococcus, Staphylococcus), and gram-negative bacilli (E. coli, Klebsiella) create mixed infection. In descending necrotizing mediastinitis, deep neck space infection (parapharyngeal, retropharyngeal) spreads caudally to the mediastinum along fascial planes — cervical fasciae show continuity to the mediastinum, allowing gravity-assisted downward progression. On CT, pneumomediastinum reflects esophageal perforation or metabolic activity of gas-producing bacteria — free air appears as very low-density foci (-1000 HU) within mediastinal fat. Obliteration of mediastinal fat planes results from inflammatory edema and cellular infiltration increasing fat density (normal fat -100 HU to inflammatory change -20 to +20 HU). Fluid collections indicate organized abscess formation — rim enhancement reflects the difference between avascular necrotic center and peripheral hyperperfused granulation tissue.
Triad of mediastinal fat plane obliteration + pneumomediastinum (free air) + rim-enhancing fluid collection (abscess) — pathognomonic CT triad of acute mediastinitis.
Obliteration of mediastinal fat planes and increased fat density — the clean low density of normal mediastinal fat (-100 HU) disappears and a hazy, increased density appearance emerges. This is the earliest CT finding and reflects diffuse inflammatory infiltration.
Report Sentence
Obliteration of mediastinal fat planes with increased density is observed, consistent with acute mediastinal inflammation.
Free air within mediastinal fat (pneumomediastinum) — appears as linear or irregular air bubbles. Pathognomonic finding in esophageal perforation. Air may extend around the esophagus, around great vessels, and into subcutaneous tissue (subcutaneous emphysema).
Report Sentence
Free air is observed within mediastinal fat indicating pneumomediastinum; esophageal perforation should be excluded.
Fluid collections in the mediastinum — organized abscess formation shows rim enhancement (peripheral thick wall enhancement + central low-density necrotic center). Air-fluid levels indicate presence of gas-producing bacteria. Collections may localize to anterior, middle, or posterior mediastinum.
Report Sentence
A fluid collection (abscess) with rim enhancement is observed in the mediastinum, and the need for emergent surgical drainage should be evaluated.
Esophageal wall thickening and/or disruption of wall integrity — focal wall defect as perforation site, periesophageal air and fluid are observed. Oral contrast extravasation confirms the perforation site when administered. Lower esophagus left posterolateral wall is the most common perforation site (Boerhaave syndrome).
Report Sentence
Focal esophageal wall thickening/defect with periesophageal air/fluid is observed, consistent with esophageal perforation.
Pleural effusion (usually left-sided in Boerhaave) and/or pericardial effusion — indicates spread of mediastinal infection to adjacent serous spaces. Empyema development manifests with septation and enhancement in pleural fluid.
Report Sentence
Left/bilateral pleural effusion and pericardial effusion are observed, consistent with spread of mediastinal infection to adjacent spaces.
In descending necrotizing mediastinitis, caudal spread from neck to mediastinum — retropharyngeal and parapharyngeal soft tissue thickening, obliteration of neck fat planes, and fluid collection showing continuity to mediastinum. Continuity between neck CT and mediastinal CT should be demonstrated.
Report Sentence
Retropharyngeal/parapharyngeal soft tissue thickening and fluid collection extending caudally from the neck to the mediastinum, consistent with descending necrotizing mediastinitis.
Criteria
Spontaneous (Boerhaave: left lower esophagus perforation after vomiting), iatrogenic (endoscopy, surgery, stent), traumatic (foreign body, corrosive). Periesophageal air, left pleural effusion characteristic.
Distinct Features
Perforation site can be confirmed with oral contrast. Mackler's triad: vomiting + chest pain + subcutaneous emphysema. Early surgical repair is critical.
Criteria
Caudal spread from deep neck infection (peritonsillar/parapharyngeal/retropharyngeal abscess, dental infection, Ludwig's angina). Neck-mediastinum fascial plane continuity demonstrated on CT.
Distinct Features
Neck CT and mediastinal CT should be evaluated together. Wide-field CT is mandatory. Aggressive surgical debridement + drainage + prolonged antibiotherapy required.
Criteria
After median sternotomy (1-5%), usually after coronary bypass or valve surgery. Sternal dehiscence, sternal osteomyelitis, retrosternal fluid collection. Develops within 2-4 weeks after surgery.
Distinct Features
Fluid around sternal wires, sternal dehiscence, retrosternal air and fluid. Differentiation from normal postoperative changes (fluid/air persisting beyond 6 weeks is suspicious) is critical. S. aureus most common pathogen.
Distinguishing Feature
Fibrosing mediastinitis shows chronic fibrous mass and calcification without acute infection findings. Acute mediastinitis presents acutely with fluid collections, pneumomediastinum, and septic picture.
Distinguishing Feature
Lymphoma presents as solid lymphadenopathies without pneumomediastinum or abscess formation. Acute mediastinitis shows fluid collections, free air, and acute infection findings.
Distinguishing Feature
Teratoma is a well-defined, heterogeneous mass containing fat-fluid-calcification. Acute mediastinitis is infiltrative, poorly defined, with fluid collections and pneumomediastinum.
Distinguishing Feature
Bronchogenic cyst is a well-defined, thin-walled, non-enhancing cystic lesion. Acute mediastinitis is infiltrative, poorly defined, with rim-enhancing fluid collections and pneumomediastinum. Infected bronchogenic cyst may mimic but remains localized.
Urgency
emergentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralAcute mediastinitis is a life-threatening surgical emergency — mortality is 40-60% without treatment, drops to 10-25% with treatment. Emergent broad-spectrum antibiotherapy should be initiated and emergent surgical drainage/debridement should be planned. In esophageal perforation, primary repair or stent placement is performed. Thoracic surgery emergency consultation is mandatory when CT findings are detected. Postoperative serial CT monitors treatment response.
Acute mediastinitis is a life-threatening emergency with mortality reaching 40-50%. Emergency surgical drainage and broad-spectrum antibiotic therapy are required. Surgical repair is performed if esophageal perforation is present. Early CT diagnosis is critical for survival.