Acute mediastinal widening.

ABSTRACT

Mediastinal abscess resulting from descending necrotizing mediastinitis is a rare infectious process. Odontogenic infections are the most commonly implicated underlying process. Descending necrotizing mediastinitis is a rapidly progressive infectious process that spreads through the fascial planes of the neck to gain access to the mediastinum. Early recognition of descending necrotizing mediastinitis is important because the reported mortality rate is 30% to 50% even in the antibiotic era. Clues to the diagnosis of descending necrotizing mediastinitis include evidence of severe oropharyngeal infection, neck swelling and crepitations, and complaints of dysphagia and odynophagia. Lateral radiographs of the neck sometimes show gas pockets, but chest films are often negative early in the disease process. A late chest x-ray finding is widening of the superior mediastinum. Therefore, computed tomography (CT) is the imaging procedure of choice. Optimal treatment includes adequate drainage of the neck and m ediastinum and broad spectrum intravenous antibiotics. Commonly implicated organisms are [alpha]-hemolytic streptococci and Bacteroides fragilis.

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DESCENDING necrotizing mediastinitis is a rare, rapidly progressive infectious process. It may result from an underlying odontogenic process. Early diagnosis is important. Clues to the diagnosis include evidence of a severe oropharyngeal infection, neck swelling and crepitations, and complaints of dysphagia and odynophagia. Early computed tomography of the neck and chest is important in the detection of descending necrotizing mediastinitis.

CASE REPORT

A 29-year-old woman had a 5-day history of cough, fever, chills, dyspnea, and pleuritic pain localized to the right upper back region. Vital signs were blood pressure 138/68 mm Hg, pulse rate 126/mm, respiratory rate 28/mm, and temperature 40.4[degrees]C. Lungs were clear to auscultation. Laboratory examination revealed a white blood cell count of 20,800/[mm.sup.3]. A chest radiograph showed a widened superior mediastinum (Fig 1). The patient also had been seen 4 days earlier, after 1 day of fever, cough, and sore throat. Chest film at that time was read as negative (Fig 2), and she was given an oral antibiotic for an upper respiratory tract infection.

Thoracic CT showed a fluid-filled mass extending from the lower neck to the mediastinum (Fig 3). A barium swallow was negative for esophageal perforation. Emergency right thoracotomy was done, with drainage of the mediastinal abscess. Cultures of the abscess were positive for [alpha]-hemolytic streptococci.

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 [beta]-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 [alpha]-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.

CONCLUSION

Descending necrotizing mediastinitis is a rapidly progressive infectious process that spreads through the fascial planes in the neck to gain access to the mediastinum. Odontogenic infections are the most commonly implicated underlying process, with [alpha]-hemolytic streptococci and B fragilis commonly being the causative organisms. Early recognition is important because of the high mortality rate. Lateral radiographs of the neck sometimes show gas pockets, but chest films are often negative early in the disease process. Computed tomography is the imaging procedure of choice. Optimal treatment includes adequate drainage of the neck and mediastinum and broad spectrum antibiotics.

References

(1.) Sakamoto H, Aoki T, Kise Y, et al: Descending necrotizing mediastinitis due to odontogenic infection. Oral Surg Oral Med Oral Pathol 2000; 89:412-419

(2.) Brook I, Frazier E: Microbiology of mediastinitis. Arch Intern Med 1996; 156:333-336

(3.) Freeman RK, Vallieres E, Verrier ED, et al: Descending necrotizing mediastinitis: an analysis of the effects of serial surgical debridement on patient mortality. J Thorac Cardiovasc Surg 2000; 119:260-267

(4.) Estrera AS, Landay MJ, Grisham JM, et al: Descending necrotizing mediastinitis. Surg Gynecol Obstet 1983; 157:545-552

(5.) Corsten MJ, Shamji FM, Odell PF: Optimal treatment of descending necrotizing mediastinitis. Thorax 1997; 52:702-708

(6.) Busch RF: Ludwig angina: early aggressive therapy. Arch Otolaryngol Head Neck Surg 1999; 125:1283-1284

(7.) Snow N, Lucas AE, Grau M, et al: Purulent mediastinal abscess secondary to Ludwig's angina. Arch Otolaryngol 1983; 109:53-55

(8.) Pane GA, Hamilton GC, Call E: Nontraumatic suppurative mediastinitis presenting as acute mediastinal widening. Ann Emerg Med 1983; 12:777-779

RELATED ARTICLE: KEY POINTS

* Descending necrotizing mediastinitis is a rapidly progressive infectious process that spreads through the fascial planes of the neck into the mediastinum.

* Early recognition of descending necrotizing mediastinitis is important because of a high mortality rate.

* Descending necrotizing mediastinitis should be suspected in a patient with evidence of severe oropharyngeal infection, neck swelling and crepitations, and complaints of dysphagia and odynophagia.

* Chest x-ray films are often negative early in the disease process. Therefore, computed tomography is the imaging procedure of choice if descending necrotizing mediastinitis is suspected.

From the Department of Internal Medicine, University of Texas Medical Branch at Galveston.

Reprint requests to Bernard Karnath, MD, University of Texas Medical Branch, Department of Internal Medicine, 301 University Blvd, 4.174 John Sealy Annex, Galveston, TX 77555.