pneumomediastinum

[nōō′mō-mē′dē-ə-stīnəm]
n.
  1. The escape of air into the mediastinal tissues, usually from interstitial emphysema or from a ruptured pulmonary bleb.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.