Mediastinitis

Mediastinitis refers to an infection or inflammation involving the mediastinum (a region in the thoracic cavity containing the heart, thymus gland, portions of the esophagus, and trachea). Acute mediastinitis can be caused by bacterial infection due to direct contamination, hematogenous or lymphatic spread, or extension of infection from nearby structures. Chronic mediastinitis, also known as fibrosing mediastinitis, is commonly related to chronic inflammatory conditions that cause the proliferation of connective tissue. Mediastinitis is treatable surgically with broad-spectrum antibiotics, as well as supportive care, depending on the etiology. Mortality from this condition is high.

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Anatomy and Etiology

Anatomy

Mediastinum:

  • Central compartment of thoracic cavity bordered by:
    • Lung pleural sacs laterally
    • Thoracic outlet above
    • Diaphragm below
  • Structures inside mediastinum:
    • Heart
    • Thymus
    • Great vessels (vena cava, aorta, pulmonary arteries)
    • Esophagus
    • Distal portion of trachea
    • Mainstem bronchi
    • Phrenic nerve
    • Vagus nerve (cranial nerve (CN) 10)

Three-dimensional rendering of high-resolution CT identifying the mediastinum:
The area highlighted in blue is the mediastinum. This area is bordered by the lung pleural sacs laterally, the thoracic outlet above, and the diaphragm below. The structures contained in the mediastinum include the heart, thymus, great vessels (vena cava, aorta, pulmonary arteries), esophagus, distal portion of trachea, mainstem bronchi, and phrenic and vagus nerves.

Image: “Mediastinum” by Mikael Häggström. License: CC0

Etiology

Acute mediastinitis:

  • Esophageal perforation:
    • Most common cause: 90%
    • History of severe vomiting 
    • Hematemesis
    • Sudden-onset neck pain and swelling
    • Painful swallowing
  • Postoperative mediastinitis:
    • One of the most common causes
    • 1%–2% of cardiac surgeries
    • Fever, chest pain, purulent or erythematous chest wound
    • Most patients present within 1 month of surgery.
  • Descending necrotizing mediastinitis:
    • Usually direct extension (retropharyngeal abscess, tonsillitis, pharyngitis, epiglottitis)
    • Worsening sore throat and/or neck swelling
    • Fever, chest pain, shortness of breath
    • Has become less frequent due to antibiotic usage

Chronic mediastinitis:

Fibrosing mediastinitis:

  • Related to long-standing inflammatory conditions
  • Marked by growth of acellular collagen and fibrous tissue within chest
  • Granulomatous mediastinitis (histoplasmosis, tuberculosis infections)
  • Non-granulomatous fibrosing mediastinitis (reaction to drugs or radiation therapy)
  • Autoimmune diseases (Behcet’s disease)

Diagnosis

History

  • Symptoms:
    • Cough
    • Fevers
    • Sore throat
    • Chest pain 
    • Painful swallowing
    • Severe vomiting
  • History of: 
    • Recent surgery
    • Autoimmune disease

Physical exam

Acute mediastinitis:

  • “Ill appearing”
  • Fever
  • Chills
  • Tachycardia
  • Chest pain
  • Odynophagia
  • CN deficits (IX, X, XI, and XII)
  • Leukocytosis
  • Wound drainage or purulent discharge

Chronic mediastinitis:

  • Insidious progression
  • Constricted airway causes cough and shortness of breath.
  • Constricted esophagus causes difficulty swallowing.
  • Constricted blood vessels cause hemoptysis and pain in chest.

Laboratory tests

  • CBC: elevated leukocytes (nonspecific for acute infection)
  • Inflammatory markers:
    • Elevated CRP
    • Elevated procalcitonin
  • Mediastinal aspiration:
    • Invasive
    • Allows for culturing and targeting of infectious agent 
  • Blood cultures:
    • May reveal bacterial pathogen
    • Especially postoperative cases

Imaging

  • Chest X-ray: 
    • Hilar mass
    • Widened mediastinum
    • Pneumomediastinum
  • CT scan: 
    • Mediastinal abscess/hilar mass
    • Swelling
    • If pericardial involvement:
      • Pericardial thickening
      • Pericardial effusion
      • Pneumopericardium
    • Fibrosing mediastinitis
      • Calcifications
      • Infiltrating mass

Management

Acute mediastinitis:

  • Antibiotics: 
    • Initially, broad spectrum
    • Culture directed when possible
  • Surgical drainage and debridement 
  • High mortality rate (10%–50%), even with appropriate treatment

Chronic fibrosing mediastinitis:

  • Lack of consensus
  • Treat underlying condition when known.
  • Medication:
    • Immunosuppressants
    • Corticosteroids
    • Antifungals
  • Surgical decompression of affected structure

Clinical Relevance

  • Retropharyngeal abscess: located behind posterior pharyngeal wall in retropharyngeal space. Usually presents with stiff neck and difficulty swallowing. Can pass from parapharyngeal to retropharyngeal space and then behind esophagus into mediastinum. Treatment involves drainage and antibiotic administration.
  • Epiglottitis: life-threatening inflammation of epiglottis and surrounding structures usually secondary to bacterial infection. Symptoms are rapid in onset and severe. Can cause airway obstruction leading to difficulty in breathing, stridor, and bluish discoloration of skin, ultimately leading to death. Diagnosis is made on direct visualization of the epiglottis by direct fiberoptic laryngoscopy in the operating room. 
  • Histoplasmosis: rare fungal infection of the lungs caused by inhaling Histoplasma capsulatum spores, often found in bat and bird droppings, which may lead to granulomatous mediastinitis. Presents with cough, shortness of breath, and difficulty breathing, accompanied by mediastinal or hilar lymph nodes (or masses), or by arthralgias and erythema nodosum. Treatment involves antifungal medication of varied durations and strengths depending on severity of infection.
  • Tuberculosis (TB): disease caused by Mycobacterium tuberculosis. Bacteria usually attack the lungs, but can also affect other parts of the body. Spreads through the air when a person infected with TB of the lungs or throat talks, sneezes, or coughs. Chronic TB infection may cause granulomatous mediastinitis.
  • Caustic ingestion: Caustic agents are acidic or alkaline substances that can severely damage organic tissues. Alkali ingestion typically damages the esophagus, whereas acids cause more severe gastric injury. Both kinds can induce laryngeal and tracheobronchial injury. Management involves securing airways, checking breathing and circulation, decontamination (remove clothes, skin irrigation), and endoscopy within 24 hours.
    Esophageal perforation:
    life-threatening condition resulting from spontaneous rupture (Boerhaave’s syndrome), iatrogenic causes (endoscopy), infectious causes, or esophageal ulcers. Present with chest pain, tachypnea, and pleural effusion. Management involves antibiotics and surgical repair. Due to its location adjacent to the mediastinum, esophageal perforation may be complicated by acute mediastinitis.

References

  1. Kappus S, King O. Mediastinitis. (2020). StatPearls. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK559266/
  2. Krüger M, Decker S, Schneider JP, Haverich A, Schega O. Therapie der akuten Mediastinitis [Surgical treatment of acute mediastinitis]. Chirurg. 2016 Jun;87(6):478-85. German. doi: 10.1007/s00104-016-0171-8.
  3. Van Wingerden JJ, de Mol BA, van der Horst CM. Defining post-sternotomy mediastinitis for clinical evidence-based studies. (2019). Asian Cardiovasc Thorac Ann 355-63. doi: 10.1177/0218492316639405.
  4. Goh SSC. Post-sternotomy mediastinitis in the modern era. (2017). J Card Surg 556-566. doi: 10.1111/jocs.13189.
  5. Patel M, Lu F, Hannaway M, Hochman K. Fibrosing mediastinitis: a rare complication of histoplasmosis. (2015). BMJ Case Rep. doi: 10.1136/bcr-2015-212774

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