Mediastinitis is inflammation of the tissues in the mid-chest, or mediastinum. It can be either acute or chronic. It is thought to be due to four different etiologies:[1] Acute Mediastinitis is usually caused by bacteria and is most often due to perforation of the esophagus. As the infection can progress rapidly, this is considered a serious condition. 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. It has a different cause, treatment, and prognosis than acute infectious Mediastinitis. Space infections: Pretracheal space – lies anterior to trachea. Pretracheal space infection leads to Mediastinitis. Here, the fascia fuses with the pericardium and the parietal pleura, which explains the occurrence of empyema and pericardial effusion in Mediastinitis. However, infectious of other spaces can also lead to Mediastinitis. Esophageal perforation, a form of direct contamination, accounts for 90% of acute mediastinal infections.[1] Esophageal perforation can arise from vomiting, incidental trauma from a procedure or operation, external trauma, ingestion of corrosive substances, malignancy, or other esophageal disease.[1] Other causes of acute Mediastinitis include infection secondary to cervical disease which arises from dental procedures, skin infections of the neck, neck trauma, or neck procedures.[1] Acute Mediastinitis is an infectious process and can cause fever, chills, tachycardia. Pain can occur with Mediastinitis but the location of the pain depends on which part of the mediastinum is involved. When the upper mediastinum is involved, the pain is typically retro-sternal pain. When the lower mediastinum is involved, pain can be located between in the scapulae and radiate around to the chest.[2] Acute Mediastinitis can be confirmed by contrast x-rays since most cases of acute Mediastinitis are due to esophageal perforation. Other studies that can be used include endoscopic visualization, Chest CT scan with oral and intravenous contrast. With regards to CT Imaging, the extent of involvement of the mediastinum can be evaluated. Therefore, acute Mediastinitis can be classified into three categories:[3] Treatment for acute Mediastinitis usually involves aggressive intravenous antibiotic therapy and hydration. If discrete fluid collections or grossly infected tissue have formed (such as abscesses), they may have to be surgically drained or debrided.[1] Descending Necrotizing Mediastinitis (DNM) was first described by Herman E. Pearse Jr., M.D. in 1938 and he stated, "the term 'Mediastinitis' means little unless qualified by a description of its type and kind."[4] Although Descending Necrotizing Mediastinitis is an acute Mediastinitis, it is distinct because it does not originate from structures within the mediastinum. Therefore, the term Descending Necrotizing Mediastinitis implies that the infection of the mediastinum originated from a primary site in the head or neck and descended through fascial spaces into the mediastinum. An observational retrospective study of 17 patients diagnosed with DNM found that the infections most often originated from neck infections including tonsillar abscess, pharyngitis, and epiglottitis. The study also found that most infections are poly-microbial.[5] Often the culprits are usually Gram-positive bacteria and anaerobes, though rarely, Gram-negative bacteria are also present. This severe form represents 20% of acute Mediastinitis cases.[6] There are specific diagnostic criteria for DNM:[7] The mortality of DNM ranges from 10-40% due to sepsis and multi-organ failure if not recognized and intervened upon early.[5] Treatment for DNM usually requires an operation to remove and drain infected necrotic tissue. Broad spectrum intravenous antibiotics are also given to treat the infection. Patients are typically managed in the intensive care unit due to the severity of the disease.[5] Chronic Mediastinitis is usually a radiologic diagnosis manifested by diffuse fibrosis of the soft tissues of the mediastinum. Two types are granulomatous Mediastinitis and fibrosing Mediastinitis. Granulomatous Mediastinitis is due to a granulomatous process of the mediastinal lymph nodes leading to fibrosis and chronic abscesses in the mediastinum. The most common causes are histoplasmosis and tuberculosis infections. Other identifiable causes include other infections (actinomycosis, nocardiosis, blastomycosis, and syphilis), IgG4-related disease and radiation therapy. Fibrosing Mediastinitis is also known as idiopathic Mediastinitis, collagenous Mediastinitis, mediastinal fibrosis, and sclerosing Mediastinitis. Mediastinal fibrosis causes problems by compressing blood vessels or airways in the mediastinum. This may result in such complications as superior vena cava syndrome or pulmonary edema from compression of pulmonary veins. Fibrosing Mediastinitis can be similar to fibrothorax.[1] Most cases of granulomatous Mediastinitis (75%) are incidentally found on chest x-rays which show a mediastinal mass. In those with symptoms, they present with symptoms of superior vena cava obstruction or esophageal obstruction.[1] Cross-sectional imaging (CT, MRI, etc.) is the preferred method of diagnosis and evaluation of the site of mediastinal involvement. This form of imaging can also allow for pre-procedure planning. Fibrosing Mediastinitis can lead to entrapment of mediastinal structures. Treatment for chronic fibrosing Mediastinitis is somewhat controversial, and may include steroids or surgical decompression of affected vessels.

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