Overview

The infection or inflammation of the mediastinum, which is a part of the chest, is known as mediastinitis. The mediastinum is situated in the center of the thoracic cavity, which contains the pleural cavity on either side of the mediastinum to hold the lungs. The mediastinum encompasses the heart and some of the vital organs like the oesophagus and major blood vessels supplying the heart. Therefore, any infection or inflammation of the mediastinum is a major concern since it will affect the functioning of many vital anatomical structures.¹

Mediastinitis can be either acute or chronic and can be caused by either infectious or non-infectious causes. Open chest surgeries or esophageal perforations lead to the majority of cases of acute mediastinitis. Descending necrotising mediastinitis is the third common type of mediastinitis.² 

This article explains the causes and risk factors associated with the development of mediastinitis.

Causes of mediastinitis

Any etiological factors that compromise the integrity of the mediastinal structure lead to the development of mediastinitis, including infectious, iatrogenic and traumatic causes. However, an inflammatory process that develops within the mediastinum results in fibrosing mediastinitis³.

Major causative factors that promote mediastinitis are as follows:

Post-surgical causes

Mediastinitis is a rare but serious complication associated with cardiac surgeries like coronary artery bypass grafting. The development of inflammation of the mediastinum increases the overall cost and results in a poor prognosis after cardiac surgery. It is also associated with increased mortality. The exact mechanism underlying the development of postoperative mediastinitis is unknown⁴. Research studies have shown that the intraoperative contamination of the wound is the major reason. The presence of various risk factors like obesity and a previous history of cardiac surgery also increases the probability of developing mediastinitis.⁵

Along with cardiac surgery, oesophagal resection is also associated with mediastinitis. Mediastinal leakage is a common complication after esophageal surgery, which in turn results in the inflammation of the mediastinum.⁶

Infectious causes

Infection that spreads from the head or neck into the chest cavity leads to the development of a form of mediastinitis known as descending necrotizing mediastinitis. Infection from above the chest, including that of an infected tooth, can travel down to the mediastinum and can damage the tissues there. Gram-positive bacteria, particularly Staphylococcus aureus and coagulase-negative Staphylococcus, accounts for about 60-80% of infectious mediastinitis. Infections associated with S. aureus mainly occur through intraoperative contamination by doctors or nurses who carry them or from the nasal passage of the patient. Coagulase-negative Staphylococcus is present in skin flora and is shown to infect surgical wounds. Along with these two, many other gram-negative bacteria and fungi like Candida species lead to infectious mediastinitis.⁷

Traumatic causes

Penetrating trauma to the chest or neck or blunt trauma leading to oesophagal rupture is also considered an etiological factor for the development of mediastinitis. Direct trauma caused by penetrating injury leads to the leakage of food, air, blood, etc, to the mediastinal space, resulting in contamination of the sterile mediastinum resulting in infection and inflammation. Blunt trauma caused by an accident or fall leads to internal damage without rupturing the skin. This can lead to microscopic tears in the mediastinal organs, including the trachea, esophagus, etc, leading to leakage of substances. In a more severe case, blunt trauma can result in organ rupture. The rupture of the oesophagus will lead to spontaneous leakage of a large amount of substance into the mediastinum, resulting in the rapid progression and development of an infection.⁸

Other causes

Spontaneous esophageal rupture (Boerhaave syndrome)

A sudden increase in intraesophageal pressure along with a negative intrathoracic pressure caused by vomiting or excessive straining causes the oesophagus to perforate in a spontaneous manner, and it is called Boerhaave Syndrome.⁹ This results in the leakage of esophageal contents into the mediastinum, resulting in mediastinitis. Late diagnosis and delay in treatment result in mortality in 40-90% of patients.¹⁰

Iatrogenic causes (e.g., Instrumentation or procedures involving the esophagus or trachea)

Esophageal injury due to iatrogenic causes is most common and is caused by endoscopic examination and intervention. Endoscopic esophageal injury mostly occurs in the upper part of the esophagus where the walls of the esophagus are thin, hence making endoscopy challenging.¹¹

Risk factors of mediastinitis

Patient-related risk factors

The occurrence of mediastinitis in certain populations possessing the following risk factors:

Obesity

Studies have shown that for every kilogram of greater body mass per square meter of body surface, there is a 3% increase in the risk of developing mediastinitis. The pathological connection between obesity and the occurrence of mediastinitis was explained by encouraged bacterial contamination, enhanced mechanical loads after surgery, inadequate antibiotic dosage and also the presence of body fat, which delays wound healing.¹²

Immunocompromised states (e.g., HIV/AIDS, Chemotherapy)

Immunocompromised individuals possess a greater risk of developing the infection and inflammation of the mediastinum as chest wall infections extend directly through the sternum. Immunodeficiency accelerates the spread of infection in the body compared to a healthy individual. Immunodeficient individuals are susceptible to infection with MRSA (methicillin-resistant staphylococcus aureus). MRSA infection is found to be more prominent in patients exhibiting risk factors like recent hospitalization, intravenous drug use, immunodeficiency, previous therapy with antibiotics, etc.¹³

Smoking and COPD

Since smoking and COPD enhance the requirement for mechanical ventilation during the recovery phase post-surgery, both of these are considered risk factors for the occurrence of mediastinitis. Smokers possess about 3.3 times higher risk of developing mediastinitis compared to the non-smoking population. The presence of COPD is associated with mechanical issues in the thoracic cavity, which further leads to the development of sternal instability.¹⁴

History of diabetes mellitus and older age are also considered risk factors for the development of postoperative mediastinitis, however, there is little evidence supporting their contribution. 

Surgery-related risk factors

The occurrence of post-surgical mediastinitis can be attributed to many surgical risk factors like the use of bilateral internal mammary artery (IMA), emergency surgery, bypass surgery, long duration of the surgery and cardiopulmonary bypass. Blood transfusion after cardiac surgery was found to cause mediastinitis as it makes people susceptible to postoperative infections. The use of intra-aortic balloons and prolonged use of mechanical ventilation are also considered risk factors for developing mediastinitis. Following strict aseptic conditions after surgery was found to reduce the risk of mediastinitis¹⁵.

Clinical presentation 

Individuals who suffer from acute mediastinitis will be ill-appearing. The common clinical manifestations associated with acute mediastinitis include chest pain, difficulty in breathing, fever, difficulty in swallowing, swelling and redness in the neck and chest. Patients suffering from descending necrotizing mediastinitis will experience the above-mentioned symptoms along with cervical and thoracic pain and an underlying infection of the head or neck. 

In the case of fibrosing mediastinitis, the patients will be asymptomatic at the beginning of the disease. However, when patients become symptomatic, they will present with cough, chest pain, fever, recurrent lung infections, etc.¹⁶

Summary

Mediastinitis is a serious infection or inflammation of the mediastinum, the central chest region containing crucial organs such as the heart, oesophagus, and major blood vessels. This condition can be acute or chronic and presents significant health risks. Primary causes include post-surgical complications, especially from cardiac surgeries and oesophagal resections, often due to intraoperative contamination. Infectious mediastinitis commonly arises from descending necrotizing mediastinitis, where infections from the head or neck spread to the mediastinum, frequently involving pathogens like Staphylococcus aureus and coagulase-negative Staphylococcus. Traumatic causes, such as penetrating or blunt chest injuries, can result in oesophageal rupture, leading to mediastinitis. Other causes include spontaneous esophageal rupture (Boerhaave Syndrome) due to sudden pressure changes from vomiting or straining and iatrogenic injuries during medical procedures such as endoscopy.

Risk factors for mediastinitis include obesity, immunocompromised states (e.g., HIV/AIDS, chemotherapy), smoking, COPD, and potentially diabetes mellitus and older age. Surgery-related risk factors involve the use of bilateral internal mammary arteries, emergency surgeries, prolonged surgery durations, cardiopulmonary bypass, blood transfusions, intra-aortic balloons, and extended mechanical ventilation. Clinically, acute mediastinitis presents with severe symptoms like chest pain, difficulty breathing, fever, and neck swelling, while descending necrotizing mediastinitis includes cervical and thoracic pain. Fibrosing mediastinitis starts asymptomatically but later causes cough, chest pain, fever, and recurrent lung infections. Prompt diagnosis and treatment are essential due to the high morbidity and mortality rates associated with mediastinitis. Understanding its causes, risk factors, and clinical manifestations is crucial for timely intervention, improving patient outcomes, and reducing complications.