The diaphragm is derived from four embryological sources which fuse in the neck and then descend:
- septum transversum; eventually forms the central diaphragmatic tendon
- pleuroperitoneal membranes
- the dorsal mesenteric mesoderm:
- eventually forms the median section of the diaphragm
- includes the crura and the mesentery around the oesophagus and vena cava
- the dorsal body wall mesoderm:
- relative enlargement of the lungs cleaves the inside surface of the body wall
- the innermost layer of this division forms the peripheral margins of the eventual diaphragm
- mesenchyme from the septum transversum migrates into this area to form skeletal muscle:
- myoblasts are derived from C3-5
- in descent, they bring their nerve supply
Failure of tissue fusion of any of the four masses can lead to potential spaces that are traversed to produce congenital diaphragmatic hernia e.g.:
- Bochdalek's foramen leading to Bochdalek's hernia
- Morgagni's foramen leading to Morgagni's hernia