SN2 SHORT NOTE 5M ★ High-yield

Describe the development of the diaphragm. Add a note on congenital diaphragmatic hernia.

Anatomy · 1st Professional — Pre-Clinical

The diaphragm develops from four sources between the 4th and 12th weeks, separating the thoracic from the abdominal cavity.

Source	Contribution	Nerve supply
Septum transversum	Central tendon	Phrenic (C3, 4, 5)
Pleuroperitoneal membranes	The paired dorsolateral parts that close the canals	Phrenic
Dorsal mesentery of the oesophagus	Crura and the median portion	Phrenic
Body wall myotomes	Peripheral muscular rim	Lower six intercostal nerves (sensory to the periphery)

Failure of the pleuroperitoneal membrane to close, usually on the left (about 85%), because the right canal closes earlier and is supported by the liver
Bochdalek hernia — posterolateral; the common congenital form
Morgagni hernia — anterior, retrosternal; rarer and often asymptomatic
Incidence about 1 in 2500
Presents with respiratory distress at birth, a scaphoid abdomen, bowel sounds in the chest and mediastinal shift
Diagnosed antenatally by ultrasound, with polyhydramnios
Treatment is stabilisation first — ventilation and pulmonary hypertension management — and repair only afterwards; operating early does not help the hypoplastic lung
Do not use bag-and-mask ventilation, which distends the herniated bowel and worsens compression; intubate and pass a nasogastric tube

Anomaly	Nature
Eventration	The muscle fails to develop but the membrane is intact; the diaphragm is thin and rises, but there is no true defect
Hiatus hernia (congenital short oesophagus)	Part of the stomach lies in the thorax
Accessory diaphragm	Rare duplication
Phrenic nerve palsy	From birth injury to the brachial plexus roots; the dome is elevated and paradoxical on inspiration

The distinction between a hernia and an eventration matters — eventration needs plication and has a far better prognosis, since the lung has not been compressed to the same degree
Referred pain to the shoulder from any subdiaphragmatic irritation is explained entirely by the embryological origin of the central diaphragm
The peripheral diaphragm is supplied by intercostal nerves, so peripheral irritation, as in basal pleurisy, is felt in the lower chest and abdominal wall instead
Associated anomalies are present in up to half of congenital diaphragmatic hernias — cardiac, neural tube and chromosomal — so a full assessment is needed

All questions in Systemic Embryology