Pediatric Pneumomediastinum

  • Etiology:
    — Barotrauma causing rupture of alveoli into pulmonary interstitium
    — Blunt thoracic trauma caused by alveolar rupture and pulmonary interstitial emphysema tracking along pulmonary interstitium to mediastinum
    — Esophageal tear from blunt thoracic trauma or forceful retching or vomiting
    — Forceful coughing through Macklin effect of alveolar rupture related to coughing against a closed glottis leading to air dissection along bronchovascular sheaths and spreading of air along pulmonary interstitium into mediastinum
  • Imaging:
    — Outlines and uplifts thymus leading to spinnaker sail sign of mediastinal air between thymus and heart
    — Continuous diaphragm sign
    — Can extend into subcutaneous tissues of neck and can extend into abdomen through diaphragmatic crus causing pneumoperitoneum and can extend into retroperitoneum causing pneumoretroperitoneum
    — Tracheobronchial injury can also have pneumothorax
  • Note: Esophagram not indicated in patients with spontaneous pneumomediastinum due to forceful coughing
  • DDX:
  • Complications: Can decrease venous return if in posterior mediastinum
  • Treatment:
  • Clinical: Can be a presentation of diabetic ketoacidosis

Radiology Cases of Pneumomediastinum

CXR and CT of pneumomediastinum
CXR AP shows air outlining the thymus (thymic sail sign) and that the diaphragm can be traced throughout its course (continuous diagphragm sign). Axial CT with contrast of the chest shows air in the posterior mediastinum in front of the spine.
CXR of tracheobronchial injury of left mainstem bronchus
CXR AP shows air in the superior mediastinum and neck, airspace disease in the left upper lobe, and a small amount of air in the left pleural space.
CXR of esophageal perforation from nasogastric tube placement
CXR AP shows air outlining the heart in the pericardial space, air outlining the thymus in the mediastinum, and air in the bilateral pleural spaces.
CXR of pulmonary interstitial emphysema
CXR AP shows a branching bubbly appearance to the right lung along with air in the superior mediastinum.
CXR of pneumomediastinum
CXR AP+lateral shows air around the thymus superiorly and air around the heart inferiorly. The diaphragm can be traced continuously across both images. There is also a small amount of air in the apex of the right pleural space.
CXR of bilateral tension pneumothoraces and pneumomediastinum
CXR AP shows a large amount of lucency in the pleural spaces laterally and inferiorly to the right lung and superiorly and inferiorly to the left lung. There is air outlining the thymus and in the neck. The mediastinum remains in the midline.
CXR of respiratory syncytial virus pneumonia / RSV
CXR AP and lateral (above) shows right upper lobe collapse and air outlining the inferior border of the heart (continuous diaphragm sign). Left lateral decubitus CXR (below) shows a small right pneumothorax.