Mediastinitis in Emergency Medicine 

Mediastinitis is an infection involving the mediastinum. It is a surgical emergency with a high mortality rate. Mediastinitis may begin primarily from structures in the mediastinum, or it may be the result of an infection extending downward from the oropharynx, in which case it is called descending necrotizing mediastinitis.

The diagnostic criteria as defined by Estrera et al and refined by Wheatley et al for descending necrotizing mediastinitis include the following:^[1]

• Clinical evidence of severe cervical infection
• Characteristic radiographic features of mediastinitis
• Documentation of necrotizing mediastinal infection at operation or at postmortem
• Establishment of the relationship between the descending necrotizing mediastinitis and the oropharyngeal infection

Infection of the mediastinum is typically polymicrobial in nature resulting from a disruption of normal mucosal and tissue barriers. Infection may result from a rupture of the esophagus or trachea or from surgical intervention. When infection extends from the head and neck downward into the mediastinum, the condition is described as descending necrotizing mediastinitis because the infection uses the fascial planes in the neck to gain access to the mediastinum. The spread downward is facilitated by gravity, breathing and negative intrathoracic pressure.^[2] It is necrotizing, as the infection is often polymicrobial in etiology with gas-producing organisms. This is the most lethal form of mediastinitis, partly due to delayed diagnosis and treatment. Odontogenic infection is the most common cause.^[3] The potential spaces that can allow infections from the head or neck to enter the mediastinum include the following:

Carotid space

The carotid sheath is a thick, matted, fibrous investment over the main longitudinal vessels of the neck. Lymph nodes are contained within the sheath, and infection in these nodes potentially could spread downward into the mediastinum. The carotid sheath extends from the arch of the aorta to the base of the skull.

Prevertebral space

This space is bounded anteriorly by the prevertebral fascia, which overlies the prevertebral muscles in the neck. The prevertebral fascia extends from the base of the skull to the lower limit of the longus colli muscle, which is approximately at the level of T3 vertebra.

Danger space

This potential space lies between the alar and prevertebral fasciae. It is patent from the skull base to the diaphragm. Its upper part is the retropharyngeal space, which lies between the prevertebral fascia and the buccopharyngeal fascia on the outer surface of the pharynx. Lymph nodes are present in this space. Seventy percent of cases of descending necrotizing mediastinitis occur in this space.^[4]

Pathological walling-off of infection usually occurs in the retropharyngeal space, but no anatomical barrier exists to the spread of infection downward into the mediastinum. The lower part of this potential space extends behind the esophagus, through the superior mediastinum, and into the posterior mediastinum. Because cervico-mediastinal spaces contain loose areolar tissue with poor vascularization and few defensive mechanisms, pathogens may easily spread across fascial planes. For this reason, any cervical infection may involve the entire mediastinum.^[1]

More than 90% of cases of acute mediastinitis are caused by esophageal rupture. This may be due to trauma (eg, MVA, chicken bone), neoplasm, surgery, or endoscopy. See Esophageal Perforation, Rupture and Tears for more detail on this subject.

Comorbid conditions (eg, diabetes) may make certain patients highly susceptible to spreading cellulitis. Mediastinitis may also result from direct extension from an adjacent source of infection including osteomyelitis of the sternoclavicular junction. Pulmonary infections may also extend into the mediastinal space. Mediastinitis may also result from extension of granulomatous disease from mediastinal lymph nodes.

Pathogens

This is often a mixed infection, with facultative and strict aerobes acting together. Obligate anaerobes usually outnumber facultative organisms by 10:1. Streptococcus species are the most common facultative organisms, while Bacteroides species are the most common strict anaerobes. Other organisms implicated include Staphylococcus, Escherichia coli, Peptostreptococcus, Fusobacterium, Haemophilus influenzae, Enterobacter cloacae, Histoplasmosis, Tuberculosis, and Pseudomonas aeruginosa.

Case reports have identified Eikenella corrodens and species of Prevotella, Stenotrophomonas, Propionibacterium, Candida, Aspergillus, and Salmonella as responsible pathogens.^[1] As the incidence of iatrogenic mediastinitis rises compared with infections acquired outside the hospital, methicillin-resistant Staphylococcus aureus infections become a cause for great concern.

Frequency

United States

Esophageal rupture is the most common cause of mediastinitis currently. Descending necrotizing infection is relatively rare in the era of antibiotic use.

International

In developing countries, mediastinitis still is a common devastating potential complication of head and neck infections.

Mortality/Morbidity

• Morbidity is significant for a mean hospital length of stay greater than 1 month, as well as a long period of outpatient recovery.^[1]
• Data suggest an overall lifetime mortality rate of 19-47%; however, a review by Ridder et al suggests an improved mortality of 11.1%.^[1]
• Studies of descending necrotizing mediastinitis in the last decade indicate mortality rates ranging between 11.1-34.9%.^[1]
• Mortality likely has improved secondary to the widespread use of antibiotics and improved oral hygiene.^[1]
• In the presence of comorbid conditions, the mortality rate for patients presenting with established infections may be as high as 67%.

Race

Age and risk factors are better predictors for the development of descending necrotizing mediastinitis than race.

Sex

Prevalence is higher among males than females, with a male-to-female ratio of 6:1.

Age

• Mediastinitis appears to be a disease of young men with a mean age in the mid fourth decade of life.
• Most persons with mediastinitis are in their third to fifth decades of life; however, case reports have documented mediastinitis in patients as young as 2 months and as old as the eighth decade.