The Many Presentations of Pneumomediastinum

Case Report

An 8-month-old boy presented with dyspnea and fever for 1 week. Chest radiography findings showed bilateral pneumonia, pneumomediastinum, and subcutaneous emphysema in the neck and axillae. Mechanical ventilation was initiated shortly after admission. The oxygen saturation and blood pressure suddenly decreased 2 days later, and the patient had decreased breath sounds and a distinctly distended abdomen. Radiography results showed bilateral pneumonia, bilateral pneumothorax, pneumomediastinum, subcutaneous emphysema in the neck and axillae, and pneumoperitoneum (Figure 1). Chest tubes were inserted, and the oxygen saturation level and blood pressure stabilized shortly afterwards. Results of repeat radiography showed the resolution of pneumoperitoneum, pneumothorax, subcutaneous emphysema, and pneumomediastinum (Figure 2). However, he died of severe pneumonia 4 days later.

Figure 1.

Chest radiography findings showing bilateral pneumothorax, subcutaneous emphysema in the neck and axillae, pneumomediastinum, and pneumoperitoneum. The accumulation of air in the anterior mediastinum (curved arrow), tubular artery sign (arrow), extrapleural sign (arrow head), and continuous diaphragmatic sign were observed together.

Figure 2.

Radiographic scan obtained 20 hours later showing resorption of pneumoperitoneum and remarkable absorption of subcutaneous emphysema, pneumothorax, and pneumomediastinum.

Discussion

Pneumomediastinum is defined as the presence of air in the mediastinum. Gas can enter mediastinal spaces from ruptured alveoli, a laceration of the tracheobronchial tree or gastrointestinal tract, and a sinus fracture or iatrogenic manipulation after dental extraction. ¹ Alveolar rupture is the most common cause of pneumomediastinum, and mechanical ventilation is a predisposing factor of pneumomediastinum.

The radiographic signs of pneumomediastinum depend on the depiction of normal anatomic structures that are outlined by the air as it leaves the mediastinum. Various radiographic signs have been well described, such us subcutaneous emphysema, the thymic sail sign, pneumopericardium, a ring around the artery sign, the tubular artery sign, double bronchial wall sign, continuous diaphragm sign, extrapleural sign, and air in the pulmonary ligament sign.^2,3 However, most of the patients presented with 1 or 2 radiographic signs. Constant mechanical ventilation or increased pressure may cause extensive pneumomediastinum. Our patient showed accumulation of air in the anterior mediastinum, tubular artery sign, continuous diaphragmatic sign, and subcutaneous emphysema simultaneously. These radiographic signs are rarely observed together.

Pneumomediastinum can lead to pneumoretroperitoneum. The increased buildup of pressure in the mediastinum because of gas leaking from the alveoli can result in perforation of the parietal pleura and pneumothorax. The air may move further caudally through the aortic and esophageal openings and the sternocostal origin of the diaphragm until it reaches the retroperitoneum space or peritoneal cavity.^3,4 Although pneumoperitoneum is usually the result of a gastrointestinal tract perforation, caution should be exercised when it occurs after pneumomediastinum. Pneumomediastinum alone has no main clinical significance; thus, physicians should treat patients on the basis of their overall clinical findings, associated injuries, and imaging findings. ⁵