Acute Mediastinal Widening

Discussion

The major causes of mediastinitis include esophageal perforation, head and neck infection, and cardiothoracic surgery. This patient most likely had descending necrotizing mediastinitis, which occurs as an extension of head and neck infections, descending down the fascial planes in the neck to gain access to the mediastinum. The infection is often polymicrobial and gas producing.

Microbiology

Odontogenic infections account for 60% to 70% of reported cases of descending necrotizing mediastinitis.^[1] A retrospective review of 17 patients with mediastinitis showed that 41% of the patients had mixed aerobic-anaerobic flora, 41% had anaerobic flora, and 18% had aerobic flora cultured from the abscess.^[2] Most aerobic organisms were found in postoperative infections, whereas most anaerobic organisms were isolated from patients with esophageal perforation, odontogenic infections, and head and neck infections. The most common pathogens in mediastinitis are the -hemolytic streptococci and Bacteroides species.

Pathways of Infection

The rapid spread of infection has been attributed to dependent drainage from the neck into the mediastinum, negative intrathoracic pressure, and synergistic bacterial growth. Lateral radiographs of the neck occasionally show abnormal collections of gas in the fascial planes. Patients often report preceding symptoms of oropharyngeal infections such as a sore throat. Patients may also report preceding symptoms of dysphagia, odynophagia, and neck swelling. The majority of descending necrotizing mediastinitis cases result from infections that spread along the retropharyngeal-retrovisceral space. Other pathways for infection to spread to the mediastinum include the pretracheal space and the parapharyngeal space.^[3]

Diagnosis and Treatment

Early diagnosis is important, and CT scanning is a more reliable tool than chest radiography. The criteria defined by Estrera et al^[4] for the diagnosis of descending necrotizing mediastinitis include (1) clinical evidence of severe oropharyngeal infection, (2) demonstration of characteristic roentgenographic features, (3) documentation of the necrotizing mediastinal infection at operation or postmortem examination or both, and (4) establishment of the relationship between descending necrotizing mediastinitis and an oropharyngeal infection. Characteristic radiologic features include widening of the retrovisceral space, anterior displacement of the tracheal air column, and presence of mediastinal emphysema. Lateral radiographs of the neck sometimes show gas pockets. Chest x-ray findings of a widened superior mediastinum frequently develop late in the course of the disease. Therefore, CT scanning is more reliable than radiography. Corsten et al^[5] recommend that CT should be done early, since it may identify abscess formation at a time when chest radiographs are still unremarkable. A CT scan may also reveal the presence of gas in the abscess that may not be detectable on plain radiographs. An overall mortality rate of 31% has been reported. Broad spectrum antibiotic therapy should be started immediately. Combined neck and thoracic drainage reduces mortality when compared with neck drainage alone.^[5]

Other Causes of Mediastinitis

Ludwig's angina, a potentially life-threatening infection involving the floor of the mouth and often resulting from periodontal infection, can spread to involve other tissues in the neck and mediastinum. Early aggressive therapy with broad spectrum antibiotic therapy and surgical decompression is warranted. Recommended antibiotic therapy includes ampicillin-sulbactam, 3 g intravenously every 6 hours, in addition to clindamycin, 600 mg IV every 6 hours.^[6]

Snow et al^[7] reported a case of Ludwig's angina that subsequently progressed to a mediastinal abscess. The patient initially presented with an abscessed molar that was extracted. By the next day, the patient had submandibular and submental swelling with crepitations in the neck. A chest film on the following day revealed a widened superior mediastinum. Air in the neck, as revealed by crepitations or gas pockets on lateral x-ray films, should alert the physician to the possibility of spreading infection. Prompt recognition and treatment of descending necrotizing mediastinitis is key to a successful outcome.^[7]

Most cases of acute mediastinitis are due to esophageal perforation, the majority of esophageal perforations being caused by instrumentation. Other causes of esophageal perforation include foreign body ingestion, emesis, trauma, and cancer erosion. The majority of mediastinal infections occur in the posterior mediastinum.

Pane et al^[8] reported mediastinitis as a complication of pneumonia. In this case, acute mediastinal widening was noted on the chest radiograph. Nontraumatic causes of mediastinitis are rare. Komatsu et al^[9] reported a case of mediastinitis resulting from purulent tonsillitis. Spread of the infection down the retropharyngeal space favored by negative intrathoracic pressure was thought to be responsible for the infection.

In our case, some of the criteria for descending necrotizing mediastinitis were met. Although the patient did not have obvious evidence of severe oropharyngeal infection, the cultures of the abscess did reveal

-hemolytic streptococci, which is common in oral flora. Characteristic findings of widened mediastinum were seen on chest films, and CT revealed a fluid-filled mass extending from the neck to the superior mediastinum. A superior mediastinal abscess was drained. No other source for mediastinal infection could be found. A barium swallow failed to reveal any esophageal abnormalities. The patient responded to surgical drainage and broad spectrum IV antibiotics.

Early diagnosis of descending necrotizing mediastinitis is important. Signs and symptoms of descending necrotizing mediastinitis include high fever, evidence of severe oropharyngeal infection, neck swelling and crepitations, dysphagia and odynophagia, and pleuritic pain that may occur between the scapulas. If these signs and symptoms occur concomitantly with a severe oropharyngeal infection, then CT scanning should be done early.

Our patient initially presented with fever, cough, and sore throat. She subsequently returned with signs and symptoms suggestive of descending necrotizing mediastinitis, including high fever, pleuritic pain in the upper back region between the scapulas, and radiographic evidence of mediastinal widening. At initial presentation, there were no signs and symptoms suggestive of descending necrotizing mediastinitis. Therefore, CT was not done.