Traumatic cervicomediastinal emphysema resulting from isolated head trauma is a rare occurrence. Herein, we describe a patient who sustained a closed mastoid injury after being struck with a batted baseball, resulting in acute extensive cervicomediastinal emphysema. Upon further assessment, the patient's aerodigestive tract was determined to have remained intact and unaffected by the injury. The source of soft-tissue air originated from the fractured mastoid. This case demonstrates the protective properties of a well-pneumatized mastoid. Furthermore, we elucidate the pathway by which the mastoid air entered and spread into the surrounding soft tissues of the neck and into the chest.