Continuous diaphragm sign.

An 11-year-old female presented to the emergency department with fever of 1 day's duration and sore throat. Her family described a 3-week history of cough with fever, trouble breathing, and wheezing. Her medical history included panhypopituitarism and asthma, and she was receiving steroid replacement therapy. She had recently undergone a dental extraction. Examination showed a temperature of 39.5°C, a 3/6 systolic murmur, bibasilar rales, and palpable cervical subcutaneous emphysema. On chest radiograph, the diaphragm appeared continuous and was not obscured by the inferior heart border (Figure 1). A computed tomography scan demonstrated the same finding (Figure 2).

Figure 1

Frontal chest radiograph. The diaphragm is not obscured by the inferior heart border (black arrows).

Figure 2

Coronal reconstruction of chest computed tomography scan demonstrates a clear space between the heart and diaphragm (black arrows).

The images depict a “continuous diaphragm sign,” an infrequent indicator of pneumomediastinum.[1] It is seen on a frontal radiograph when gas in the mediastinum separates the heart and the superior surface of the diaphragm, and it can be seen on either upright or supine views.[1,2] A continuous diaphragm may also be seen with pneumopericardium, although it is much less common.[3,4] Distinguishing the 2 conditions radiographically can be challenging, but pneumopericardium typically appears as an isolated broad band around the heart rather than the multiple thin lucent streaks extending into neck seen with pneumomediastinum.[3]

Pneumomediastinum occurs after alveolar rupture as gas travels along the bronchovascular interstitial sheaths into the mediastinum.[3,5] Nontraumatic causes include invasive procedures and mechanical ventilation, airway obstruction, barotrauma, and pulmonary or pericardial infections, and it has also been described after dental extractions.[3-6] Spontaneous pneumomediastinum is rare and usually benign, and tends to occur in males and younger patients.[7,8] Common symptoms of pneumomediastinum are chest pain and dyspnea, and signs are subcutaneous emphysema, wheezing, and Hammon sign.[3,7,8] Differential diagnoses include pneumothorax and esophageal rupture, and complications include hypotension from impaired venous return, tension pneumothorax, and cardiac tamponade.[3,4,7]

Most cases follow a benign course and require no therapy, although in 1 series prophylactic antibiotics were given and all cases resolved without complication.[8]