Coexistent diaphragmatic herniation and eventration: Embryologic rationale for therapeutic interventions

Diaphragmatic herniation and eventration are distinct entities that may be congenital or acquired and rarely occur simultaneously. Safe patient care requires differentiation of the two processes. We present an adult patient with coexistent diaphragmatic herniation and eventration to demonstrate the embryologic basis of the two conditions, elucidate the diagnosis, and discuss safe therapeutic intervention. Herniation indicates a structural defect in an otherwise normal diaphragm. Eventration applies to defective muscular content or innervation in a structurally intact diaphragm. Normal diaphragmatic structure and development may be understood as the sum of four component parts: septum transversum, pleuroperitoneal membranes, dorsal mesentery, and striated muscle masses. A failure of myoblast migration and, therefore, neural innervation on the right can produce ipsilateral eventration and a hiatus hernia. During the course of laparotomy for an unrelated process such as acute calculous cholecystitis, hernia repair should be avoided so as to avoid injury to the normal contralateral phrenic nerve, the posterior branch of which being particularly vulnerable. By depriving the patient of innervation to the only functional hemidiaphragm, contralateral neural injury can result inacute respiratory paralysis and patient mortality. © 1994 Wiley‐Liss, Inc.