Anatomy of the Diaphragm
Embryology, the three openings, phrenic nerve, and phrenotomy principles.
The diaphragm is a dome-shaped musculotendinous structure forming the floor of the thoracic cavity and the roof of the abdominal cavity. It has a central tendinous portion and a peripheral muscular portion comprising sternal, costal, and lumbar components.
Embryology
During gestation, the diaphragm begins developing at week 4 and is complete by week 10. It derives from four embryological structures:
| Embryological structure | Adult counterpart |
|---|---|
| Septum transversum | Central tendon |
| Pleuroperitoneal membranes (right and left) | Posterolateral muscular diaphragm |
| Somites (C3–C5 myotomes) | Peripheral muscular diaphragm |
| Mesentery of the oesophagus | Crural / lumbar part |
Gross anatomy
Muscular components and origins
- Sternal part: two slips from the posterior surface of the xiphoid process
- Costal part: inner surfaces of the lower 6 ribs and their costal cartilages — interdigitates with transversus abdominis
- Lumbar (crural) part: right crus from L1–L3; left crus from L1–L2; medial and lateral arcuate ligaments (thickenings of the fascia over psoas major and quadratus lumborum respectively)
Openings of the diaphragm
| Level | Opening | Structures transmitted |
|---|---|---|
| T8 | Vena caval foramen | IVC · right phrenic nerve |
| T10 | Oesophageal hiatus | Oesophagus · left and right vagus nerves · oesophageal branches of left gastric vessels · lymphatics |
| T12 | Aortic hiatus | Aorta · thoracic duct · azygos vein |
I 8 10 Eggs At 12 — IVC at T8 · oEsophagus at T10 · Aorta at T12
Additional structures passing through the diaphragm
- Left phrenic nerve — pierces the left dome of the diaphragm directly (not via a named foramen)
- Greater, lesser, and least splanchnic nerves — through the crura
- Sympathetic trunks — posterior to the medial arcuate ligaments
- Hemiazygos vein — through the left crus
Nerve supply — phrenic nerve
The phrenic nerve arises from the anterior rami of C3, C4, and C5 — predominantly C4. It is the sole motor supply to the diaphragm and also provides sensory supply to the central diaphragmatic peritoneum (referred pain to the shoulder tip — C4 dermatome).
Course: Descends through the neck lateral to scalenus anterior → crosses the thoracic inlet anterior to the subclavian artery → descends in the middle mediastinum anterior to the lung root.
- Right phrenic nerve: passes through the vena caval foramen with the IVC at T8
- Left phrenic nerve: pierces the muscular diaphragm separately, anterior to the left dome
- Terminal branches: anterior, lateral, and posterior — run in the intramuscular plane between thoracic and abdominal surfaces, providing segmental innervation
Incisions in the diaphragm must be carefully planned to avoid transection of terminal phrenic branches. The circumferential incision (2–3 cm parallel to the costal attachment) provides wide abdominal access with minimal risk to the innervation. The radial incision is placed between the lateral and posterior terminal branches. On the right, phrenotomy provides excellent access to the dome of the liver (useful for combined lung-liver hydatid or hepatic abscess). On the left, it provides access to the stomach, spleen, pancreas, and distal oesophagus.
Blood supply
The rich dual blood supply (both thoracic and abdominal) makes pedicled diaphragmatic flaps an excellent option for buttressing bronchial stumps, closing oesophageal defects, and chest wall reconstruction.
Surgical approaches to the diaphragm
| Approach | Indications | Notes |
|---|---|---|
| Posterolateral thoracotomy | Thoracic pathology with diaphragm involvement; trauma; right-sided diaphragm repair | Standard approach; excellent diaphragm exposure |
| Thoracoabdominal incision | Combined thoracic and abdominal pathology (e.g. oesophageal cancer) | Excellent bilateral exposure; divides costal margin |
| Laparoscopy | Hiatal hernia; eventration; chronic traumatic hernia | Bilateral diaphragm access; magnified view; preferred for elective procedures |
| Laparotomy (midline / subcostal) | Diaphragmatic injury with associated abdominal injury | Rapid access in haemodynamically unstable patient |
All clinical content should be verified against current guidelines before clinical application. This resource is intended for revision and educational purposes only.
Standard textbooks
- Shields TW, LoCicero J, Reed CE, Feins RH. General Thoracic Surgery. 7th ed. Lippincott Williams & Wilkins.
- Sellke FW, del Nido PJ, Swanson SJ. Sabiston & Spencer Surgery of the Chest. 9th ed. Elsevier.
- Pearson FG, et al. Thoracic Surgery. 3rd ed. Churchill Livingstone.