Everything about anatomy of diaphragm in brief

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Anatomy of the Diaphragm

Overview

The diaphragm is a dome-shaped musculotendinous partition that separates the thoracic and abdominal cavities by sealing the inferior thoracic aperture. It is the primary muscle of inspiration - when it contracts, its domes flatten and thoracic volume increases, drawing air into the lungs. - Fischer's Mastery of Surgery, 8th ed.

Structure

The diaphragm has two components:

1. Muscular Part - Peripheral fibers arise radially from the margins of the inferior thoracic aperture and converge centrally.

2. Central Tendon - The aponeurotic center into which all muscle fibers insert. It is trifoliate (three-leafed) in shape, extends further anteriorly than posteriorly, and blends with the fibrous pericardium above. During respiration, the central tendon moves while the peripheral attachments remain fixed. - Fischer's Mastery of Surgery

The right dome rises higher (reaching rib V) than the left dome, partly because the liver supports it from below. - Gray's Anatomy for Students

Origin (Peripheral Attachments)

The diaphragm has three parts of origin:

Part	Origin
Sternal part	Two muscular slips from the posterior surface of the xiphoid process
Costal part	Inner aspect of costal cartilages and ribs 7-12
Lumbar part	Right crus (L1-L3/4), Left crus (L1-L2/3), via anterior longitudinal ligament

Arcuate ligaments of the lumbar part:

Median arcuate ligament - joins the two crura in the midline, arches over the aorta
Medial arcuate ligament (medial lumbocostal arch) - from the body of L2 to its transverse process, over psoas major
Lateral arcuate ligament (lateral lumbocostal arch) - from the transverse process of L2 to the tip of the 12th rib, over quadratus lumborum

A muscular weak spot called the lumbocostal trigone (Bochdalek triangle) exists between the costal and lumbar parts - a common site of congenital diaphragmatic hernia. - Fischer's Mastery of Surgery

Openings (Hiatuses)

There are three major openings, memorized by the mnemonic "8, 10, 12":

Diaphragm openings at vertebral levels T8, T10, T12

Opening	Level	Structures Passing Through
Caval opening	T8	IVC, right phrenic nerve, lymphatics
Esophageal hiatus	T10	Esophagus, anterior + posterior vagal trunks, left gastric artery and vein
Aortic hiatus	T12	Aorta (posterior to median arcuate ligament), thoracic duct, azygos vein

Additional smaller openings:

Sternocostal hiatus (foramen of Morgagni / space of Larrey) - between sternal and costal parts; transmits the superior epigastric artery (branch of internal thoracic artery) and lymphatics from the liver. A retrosternal/parasternal hernia can occur here.

The esophageal hiatus is formed mainly by fibers of the right crus, which split to surround the esophagus like a sphincter. There is considerable variation (shown in the diagram below): - Fischer's Mastery of Surgery

Inferior view of diaphragm showing crura, hiatuses, and their anatomical variations

Nerve Supply

Motor + Sensory (central):

Phrenic nerves (C3, C4, C5 - "C3, 4, 5 keeps the diaphragm alive")
They descend on the lateral surface of the fibrous pericardium, anterior to the lung root, and enter the diaphragm medially
The left phrenic nerve enters the muscular part of the left hemidiaphragm just lateral to the cardiac surface
The right phrenic nerve passes through the caval opening or central tendon
Each phrenic nerve branches into: sternal (anteromedial), anterolateral, posterolateral, and crural branches

Sensory (peripheral):

Intercostal nerves 9-11 supply the periphery of the diaphragm

Sympathetic fibers also reach the diaphragm via the inferior phrenic plexus (from the celiac plexus). - Fischer's Mastery of Surgery

Blood Supply

Surface	Arterial Supply	Venous Drainage
Superior (thoracic)	Superior phrenic aa. (from thoracic aorta), musculophrenic + pericardiophrenic aa. (from internal thoracic)	Superior phrenic veins → azygos/hemiazygos
Inferior (abdominal)	Inferior phrenic aa. (branches of abdominal aorta or celiac trunk)	Inferior phrenic veins → IVC and left suprarenal vein

The inferior phrenic arteries are the main supply to the abdominal surface. - Fischer's Mastery of Surgery

Lymphatic Drainage

Superior surface - drains to anterior, middle, and posterior phrenic lymph nodes
Inferior surface - drains to phrenic nodes (lymphatics pierce the diaphragm) and to aortic (para-aortic) nodes (following the inferior phrenic vessels)

Relations

Side	Relations
Superior (thoracic)	Heart + pericardium (centrally), pleura + lungs (peripherally)
Inferior (abdominal)	Liver (right), stomach + spleen (left), kidneys and adrenals (posteriorly)

The costodiaphragmatic recess - the pleural recess between the thoracic wall and diaphragm - is the most clinically important recess; it accommodates lung expansion during deep inspiration. - Gray's Anatomy for Students

Structures That Pass Posterior to the Diaphragm (Not Through It)

The sympathetic trunk, splanchnic nerves, and the azygos/hemiazygos veins pass posterior to the diaphragm under the medial and lateral arcuate ligaments rather than through a formal hiatus.

Clinical Correlates

Hiatus hernia - herniation through an enlarged esophageal hiatus (most common diaphragmatic hernia in adults)
Bochdalek hernia - congenital defect through the lumbocostal trigone, usually on the left; presents in neonates with respiratory distress
Morgagni hernia - through the sternocostal hiatus; usually right-sided, often asymptomatic in adults
Referred pain - phrenic nerve irritation (e.g., subphrenic abscess, ruptured spleen) causes referred pain to the shoulder tip (C4 dermatome)

Verterbral origin

The vertebral (lumbar) origin of the diaphragm is via the crura and arcuate ligaments:

Right crus: L1 - L3 (sometimes L4)
Left crus: L1 - L2 (sometimes L3)
Median arcuate ligament: joins the two crura, arches over the aorta
Medial arcuate ligament: L2 body → L2 transverse process (over psoas major)
Lateral arcuate ligament: L2 transverse process → 12th rib tip (over quadratus lumborum)

From the previous textbook content already in context (Fischer's Mastery of Surgery), here is the detailed breakdown:

Vertebral Origin of the Diaphragm (Lumbar Part)

Crura

The crura are tendinous at their origin, blending with the anterior longitudinal ligament of the vertebral column:

Crus	Vertebral Levels
Right crus	L1 to L3/L4 vertebral bodies, intervertebral discs, and anterior longitudinal ligament
Left crus	L1 to L2/L3 vertebral bodies, intervertebral discs, and anterior longitudinal ligament

The right crus is longer and larger than the left, because the aorta pushes the origin further to the right.
The two crura are joined anteriorly by the median arcuate ligament, which arches over the front of the aorta at the T12/L1 level to form the aortic hiatus.
Fibers of the right crus diverge and reconverge around the esophagus to form the esophageal hiatus (in most people).

Arcuate Ligaments

These are thickenings of the fascia covering posterior abdominal muscles - they serve as additional "ligamentous" vertebral origins:

Ligament	From	To	Structure it arches over
Median arcuate ligament	Left crus	Right crus (midline junction)	Aorta (+ thoracic duct)
Medial arcuate ligament	Body of L2	Transverse process of L2	Psoas major muscle
Lateral arcuate ligament	Transverse process of L2	Tip of 12th rib	Quadratus lumborum muscle

Weak Points at the Vertebral Origin

Lumbocostal trigone (Bochdalek triangle) - a small triangular gap between the costal and lumbar parts of the diaphragm, just medial to the lateral arcuate ligament. It is covered only by connective tissue (no muscle). This is the commonest site of congenital diaphragmatic hernia (Bochdalek hernia), which is typically left-sided (because the right side is protected by the liver).
Structures that sneak under the arcuate ligaments (do not pierce the diaphragm):
- Under the medial arcuate ligament: sympathetic trunk, greater/lesser/least splanchnic nerves
- Under the lateral arcuate ligament: subcostal nerve and vessels
Fischer's Mastery of Surgery, 8th ed.

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