Mediastinitis overview

# Overview
Mediastinitis is inflammation or infection of the tissues in the mid-chest, or mediastinum. This disorder is rare, but is most often observed among patients following chest surgery or endoscopy. Mediastinitis may occur at any age. It may be classified according to cause into 2 groups: acute or chronic (sclerosing or fibrosing). Acute mediastinitis is usually bacterial and due to rupture of organs in the mediastinum. Chronic sclerosing (or fibrosing) mediastinitis, while potentially serious, is caused by a long-standing inflammation of the mediastinum, leading to growth of acellular collagen and fibrous tissue within the chest and around the central vessels and airways. Life threatening causes of mediastinitis include esophageal perforation.  Common causes of mediastinitis include trauma, beta-hemolytic streptococcus, forceful or constant vomiting, and median sternotomy. If left untreated, fibrosing mediastinitis may progress to sepsis and subsequently, death. The presence of mediastinitis among patients following chest surgery is observed to have a particularly poor prognosis; there is a serious risk of mortality. Common complications of mediastinitis include sepsis and spread of the infection. Symptoms of mediastinitis include chest pain, malaise, and shortness of breath. Common physical examination findings of mediastinitis include clinical signs of sepsis, tachycardia, and tachypnea. CT scan  may be diagnostic of mediastinitis. On CT scan, findings suggestive of mediastinitis include the presence of calcified mediastinal mass. The mainstay of therapy in acute mediastinitis secondary to cardiothoracic surgery includes clindamycin and ceftriaxone. The preferred regimen for preoperative prophylaxis against acute mediastinitis includes either a second generation cephalosporin or vancomycin. Aggressive surgical debridement is recommended among patients with descending necrotizing mediastinitis.

# Historical Perspective
Chronic mediastinitis was first described by Dr. Thomas T. Whipham, MD, a British physician, in 1899.

# Classification
Mediastinitis may be classified according to cause into 2 groups: acute or chronic (sclerosing or fibrosing). Additionally, acute mediastinitis may be classified according to the cause of the disease.

# Pathophysiology
Mediastinitis is the inflammation or infection of the mediastinum. The pathogenesis of the infection remains unknown; radiographic, serologic, and/or histopathologic evidence of prior Histoplasma capsulatum infection, histoplasmosis, or chronic granulomatous disease is always observed. Additionally, mediastinitis may also present as the result of Staphylococcus aureus or Staphylococcus epidermidis infection following chest surgery.

# Causes
Common causes of mediastinitis include bacterial and fungal infections, including group A beta-hemolytic streptococci, Mycobacterium tuberculosis, and Histoplasma capsulatum. 

# Differentiating Mediastinitis from Other Diseases
Mediastinitis must be differentiated from other diseases that cause fever and chest pain, such as myocardial infarction, pneumothorax, and pneumonia.

# Risk Factors
The most potent risk factor for mediastinitis is recent chest surgery. Other risk factors include recent endoscopy, smoking, and obesity.

# Natural History, Complications and Prognosis
If left untreated, fibrosing mediastinitis may progress to sepsis and subsequently, death. Mortality rates related to mediastinitis vary, though some estimates predict rates greater than 60%. Common complications of mediastinitis include sepsis and pneumonia.

# Diagnosis

## Diagnostic Criteria
The diagnosis of mediastinitis is based on the CDC criteria, which includes histopathologic evidence, imagining findings, and other positive findings.

## History and Symptoms
Specific areas of focus when obtaining a history from the patient include chest surgery, pharyngeal surgery, and endoscopy. Symptoms of mediastinitis include chest pain, cough, chills, and shortness of breath.

## Physical Examination
Common physical examination findings of mediastinitis include clinical signs of sepsis, tachycardia, and tachypnoea.

## Laboratory Findings
Laboratory findings consistent with the diagnosis of mediastinitis include positive confirmation of organisms found upon sternal culture during chest surgery or fine needle aspiration of the mediastinum including Staphylococcus aureus and Histoplasma capsulatum.

## Chest X Ray
On chest x-ray, mediastinitis may be characterized by calcification, widening of the mediastinum, and increased right hilar bronchovascular bundles. The chest x-ray findings associated with mediastinitis are very non-specific.

## CT
On CT scan, the appearance of mediastinitis can be variable and dependent on the pattern of involvement. Typically, the disease affects the middle mediastinum and may demonstrate mediastinal or hilar mass, infiltrative regions of soft-tissue attenuation which obliterate normal mediastinal fat planes and encase or invade adjacent structures, or calcifications of the central mass or associated lymph nodes (especially if there has been preceding histoplasmosis).

## MRI
On MRI, mediastinitis is characterized by mediastinal or hilar mass or soft-tissue attenuation. Pattern of involvement is essentially similar to CT scan for mediastinitis.

## Other Imaging Findings
Other diagnostic studies for mediastinitis include positron emission tomography and fiberoptic bronchoscopy.

# Treatment

## Medical Therapy
The mainstay of therapy in acute mediastinitis secondary to cardiothoracic surgery includes clindamycin and ceftriaxone. The preferred regimen for preoperative prophylaxis against acute mediastinitis includes either a second generation cephalosporin or vancomycin.

## Surgical Therapy
Aggressive surgical debridement is recommended among patients when combined with broad spectrum antibiotics that provide coverage against MRSA, beta-lactamase producing gram-negative organisms, and anaerobes.

# Prevention

## Primary Prevention
Effective measures for the primary prevention of mediastinitis include nasal decolonization, hand hygiene, and antibiotic prophylaxis.

## Secondary Prevention
Effective measures for the secondary prevention of mediastinitis following sternotomy include reporting wound discharge to physician and aggressive treatment of hyperglycemia.