Eye Test - the Answer

So the plain films (see photo album on Rob's Radiology fan page on Facebook) demonstrate subcutaneous emphysema and air streaks outlining the mediastinum and proximal vessels. This is consistent with:

Pneumomediastinum.

• Pneumomediastinum - air in the mediastinum
• Sources
• - rupture of alveoli - most common cause - increased pressure (ventilator, mucous plug, foreign body, strain against closed glottis) or damage of cells (pneumonia, emphysema, ARDS)
• - laceration of tracheobronchial tract
• - GI tract (esp esophagus)
• - passage of air from head and neck (sinus fx, dental extraction, vascular channels etc), retroperitoneum, chest wall
• The mediastinum communicates with the submandibular space, retropharyngeal space and vascular sheaths in the neck
• The retroperitoneum communicates with the mediastinum through the sternocostal insertion of the diaphragm which also communicates with flanks and pelvis
• Retroperitoneum also communicates through the periaortic and periesophageal spaces
• Clinically - often asymptomatic. Can cause dyspnea and chest pain
• Complications - can cause pneumothorax; rarely - cause hypotension due to decreased venous return to the heart from high pressure in pneumomediastinum
• Features
• Radiograph - look for lucent streaks and bubbles - especially a pleural line above the left heart lateral to PA and aortic arch on frontal view
• Lateral View - Air may outline ascending aorta, PA, trachea and bronchi; can outline thymus, sternal insertion of diaphragm and brachiocephalic veins.
• Lateral - can see air outline anterior to the heart - in a "pneumoprecardium"
• Continuous diaphragm - air between diaphragm and pericardium
• Naclerio's V sign - air along descending aorta inserts into an insertion along left hemidiaphragm and forms a V shape (frontal view)
• Ring around the artery sign - air around right pulmonary artery (best seen on lateral)
• infants - thymic spinnaker sign
• Can also get apical cap of lucency - can look like pneumothorax but won't move with position
• Pneumomediastinum usually doesn't completely surround the heart and usually has multiple thin streaks

Vs. Pneumopericardium

• Usually from penetrating trauma or recent heart surgery
• If from ventilator will have pneumomediastinum usually as well - but requires much higher pressures than pneumomediastinum
• Not as common as Pneumomediastinum
• Often a complete band seen around left ventricle and right atrium
• Does not usually extend into the neck or upper mediastinum
• Halo sign - band around the entire heart
• May outline ascending aorta and main PA but does not extend to arch or trachea
• Pneumopericardium - can change with position but pneumomediastinum won't

References - http://www.ajronline.org/cgi/reprint/166/5/1041 ; http://radiographics.rsnajnls.org/cgi/content/full/20/4/1043 ; and Primer of Diagnostic Imaging by Weissleder et al.