41. Mediastinitis

1. Definition

• Mediastinitis → inflammation of the connective tissue of the mediastinum
• Acute mediastinitis → bacterial infection that spreads fast along fascial planes; a surgical emergency
• Chronic (fibrosing) mediastinitis → slow, dense fibrosis of the mediastinum that compresses its structures

2. Epidemiology

• Post-sternotomy mediastinitis → 0.5–2% of cardiac operations; mortality 10–25%
• Descending necrotising mediastinitis → rare; from neck infection; mortality up to 40%
• After oesophageal perforation → mortality 10–25% if treated within 24 h, higher if later
• Fibrosing mediastinitis → young adults; regions with histoplasmosis

3. Aetiology and risk factors

Acute mediastinitis

• Oesophageal perforation → most common cause outside cardiac surgery:
  • Iatrogenic → endoscopy, dilatation (about 60%)
  • Boerhaave's syndrome → rupture after forceful vomiting, left posterolateral distal oesophagus
  • Foreign body, trauma, anastomotic leak after oesophagectomy
• Post-sternotomy → deep sternal wound infection:
  • Diabetes, obesity, COPD, smoking
  • Bilateral internal mammary artery grafts
  • Long operation, re-exploration for bleeding
• Descending necrotising mediastinitis → spread from:
  • Odontogenic infection, Ludwig's angina
  • Retropharyngeal or peritonsillar abscess
• Tracheobronchial injury, spread from lung, pleura or vertebra
• Organisms → mixed aerobes and anaerobes from the mouth; S. aureus and S. epidermidis after sternotomy

Chronic mediastinitis

• Histoplasmosis (most common), tuberculosis
• Sarcoidosis, radiotherapy, IgG4-related disease, drugs (methysergide)

4. Pathogenesis

• Mediastinum has no barriers → infection spreads along fascial planes
• Neck to mediastinum → three routes:
  1. Pretracheal space → anterior mediastinum
  2. Perivascular (carotid sheath) → middle mediastinum
  3. Retropharyngeal and "danger space" → posterior mediastinum (most common, about 70%)
• Oesophageal perforation → saliva, gastric juice and bacteria enter the mediastinum → chemical then bacterial mediastinitis → sepsis
• Negative intrathoracic pressure draws contents in; pleura often breaks → empyema
• Fibrosing form → granulomatous inflammation → fibrosis that encases the SVC, airways, pulmonary vessels and oesophagus

5. Classification

• By course → acute, chronic
• By cause:
  • Post-sternotomy (deep sternal wound infection)
  • Post-perforation (oesophagus, airway)
  • Descending necrotising (from the neck)
  • Secondary (lung, pleura, spine, subphrenic)
• Post-sternotomy by time (El Oakley) → type I (within 2 weeks) to type V (recurrent)
• Descending necrotising (Endo) → type I above the carina; type IIA lower anterior; type IIB anterior and lower posterior

6. Clinical picture

Symptoms

• Retrosternal chest pain, often severe, spreading to the back or neck
• Fever > 38 °C, rigors
• Dysphagia, odynophagia
• Dyspnoea
• Boerhaave's → vomiting, then chest pain and collapse (Mackler's triad → vomiting, chest pain, subcutaneous emphysema)
• Post-sternotomy → wound discharge, sternal pain, sternal "click"
• Neck infection → neck pain, swelling, trismus

Signs

• Tachycardia, tachypnoea, hypotension → sepsis
• Subcutaneous emphysema of the neck
• Hamman's sign → crunching sound with the heartbeat (air in the mediastinum)
• Sternal instability, purulent drainage
• Pleural effusion, signs of pneumothorax
• Fibrosing form → SVC syndrome, cough, haemoptysis, dysphagia

7. Diagnosis

Laboratory

• Leucocytosis, high C-reactive protein, procalcitonin, lactate
• Blood cultures
• Wound swab, mediastinal fluid culture
• Pleural fluid with high amylase or food particles → oesophageal perforation

Imaging

• Chest X-ray → widened mediastinum, pneumomediastinum, air-fluid levels, left effusion
• Contrast CT of neck and chest → test of choice:
  • Fluid collections, gas in the mediastinum
  • Spread from the neck
  • Sternal separation, retrosternal collection
• Water-soluble contrast swallow (Gastrografin), then barium if negative → site of perforation
• Flexible endoscopy → careful, in theatre; can show and treat the leak
• Fibrosing form → CT with calcified nodes; histoplasma serology; biopsy to exclude cancer

8. Differential diagnosis

• Myocardial infarction, aortic dissection
• Pulmonary embolism
• Pericarditis
• Perforated peptic ulcer, acute pancreatitis
• Spontaneous pneumomediastinum (no infection)
• Lymphoma, mediastinal tumour (fibrosing form)

9. Treatment

Conservative

• Resuscitation → IV fluids, oxygen, ICU
• Broad-spectrum IV antibiotics → cover aerobes, anaerobes and fungi (e.g. piperacillin-tazobactam or carbapenem ± antifungal)
• Nil by mouth, nasogastric tube, PPI
• Nutrition → feeding jejunostomy or parenteral
• Contained small perforation, no sepsis → non-operative care with antibiotics and drainage
• Fibrosing mediastinitis → no proven drug; stents for SVC, airway or pulmonary vessels

Surgical

• Aim → remove the source, debride and drain
• Oesophageal perforation:
  • Early (< 24 h), healthy tissue → primary two-layer repair, buttressed with pleura, intercostal muscle, diaphragm or omentum; drain the chest
  • Late or friable → T-tube drainage, or endoscopic stent or vacuum therapy
  • Severe, with diseased oesophagus (cancer, achalasia) → oesophagectomy, or exclusion with cervical oesophagostomy and gastrostomy
  • Approach → left thoracotomy for distal tears, right thoracotomy for mid-oesophagus, neck for cervical tears
• Descending necrotising:
  • Neck drainage plus mediastinal drainage
  • Below the carina → thoracotomy or VATS debridement
  • Tracheostomy if the airway is threatened
• Post-sternotomy:
  • Open the wound, remove wires, debride bone and cartilage
  • Negative pressure wound therapy (VAC)
  • Then closure with rewiring or pectoralis major or omental flap
• Fibrosing → surgery only for bypass of a blocked SVC or a resectable mass

10. Complications

• Septic shock, multiorgan failure
• Empyema, pericarditis, tamponade
• Erosion of great vessels → haemorrhage
• Tracheo-oesophageal fistula
• Sternal non-union, osteomyelitis
• Fibrosing → SVC syndrome, pulmonary hypertension, haemoptysis