Diaphragm Anatomy

• The diaphragm is a wide, thin, flat muscle which separates the thorax from the abdomen.
• It has the shape of a dome with superior convexity
• It inserts on the lower circumference of the thorax and is notched at the back by the projection of the thoracolumbar vertebral column
• The center presents a tendinous formation
• Numerous organs from the thorax pass through it

Diaphragm Characteristics

• This unpaired muscle presents two parts: one on the right and one on the left
• The diaphragm has double innervation
• Automatism occurs through nervous impulses

Insertions and Anatomical Constitution

• The lumbar vertebrae
• The costal, chondral, and sternal
• The tendinous center
• The anatomical constitution of the muscle includes the right and left cupolas, foramen, and hiatus

Lumbar Portion of the Diaphragm

• Represented by solid and inextensible fibrotendinous cords; from where denomination of right and left pillars comes
• The main pillars are anterior
• Accessory pillars are lateral
• The third pillars are present

Main Pillars

• Two main pillars are distinguished, one on the right and one on the left of the median line

• The right pillar is inserted on the anterior face of the 1st, 2nd, and 3rd lumbar vertebrae and on the corresponding intervertebral discs

• It sometimes descends to the 4th lumbar vertebra

• The left pillar inserts on the 1st and 2nd lumbar vertebrae and on the corresponding discs

• Sometimes descending to the 3rd lumbar vertebra

• The two pillars emit fibres by their medial border that cross each other in the midline

• Arches can be formed below vertebral body concavities

• The lumbar arteries pass under this arch

• The upper end of each pillar emits muscular fibers

• Medial fibers overlap those coming from the opposite side to form the aortic hiatus in front of the vertebral column

• Lateral fibers attach to the accessory pillar

• Median fibers run vertically towards the tendinous center, while others run obliquely, crossing and arranged in 8 around the aortic and oesophageal hiatuses

Accessory Pillars

• Located to the right and left of the main pillars
• Each inserts on the lateral face of the vertebral body of the 2nd lumbar and of the II-L2 disc
• Behind and lateral to the corresponding main pillar

Accessory Pillar Origin Points

• Medial fibers adhere to fibers from main pillar

• Lateral fibers describe a caudally concave curve to fix on the end of first lumbar vertebra's rib apophysis

• Forms the medial arcuate ligament

• The psoas muscle passes below this ligament

• Its concavity adheres to the iliac fascia psoas portion

• Its convexity originates muscular fibers

• There are third pillars

• It's a transition between vertebral and costal insertions

• Detaches from first lumbar vertebra's rib's apex

• As it passes in front of the quadratus lumborum muscle, it describes a curve that leads to the free end of the 12th rib or 11th when the 12th is short

• This third pillar is also known as the lateral arcuate ligament

Costal Portion of the Diaphragm

• Laterally, the fibers attach to the medial face of the last ribs and cartilage through digitations

• Two extended arches are distinguished

  • The 1st from 12th to the 11th rib medial face apex
  • The 2nd from 11th to 10th rib anterior end

• These are known as Senac's arcades

  • The insertion on the 9th is chondrocostal
  • On the 8th it is condrolateral
  • On the 7th it is mediocondral

Sternal Portion

• Attaches to posterior face of xiphoid apophysis using two slips
• Fascicles separated by small connective space: the median hiatus of the sternal part of Marfan
• The sternal insertions are separated from the costal portion by the sternocostal triangle of Larrey

Tendinous Center

• Found between all the muscular fibers
• Acts as an insertion for the circumference of the lower thorax
• Forms a brilliant, nacred fibrous sheet ("Von Helmont's mirror")
• Has a trefoil shape with 3 leaflets

Tendinous Center Leaflets

• The leaflets are named anterior, lateral right, and lateral left

• The lateral leaflets are separated from the posterior notch

• The anterior leaflet is widest, but shortest

• The right leaflet is oblique to the back and right, attached to the anterior leaflet by a narrower segment, where the foramen of the inferior vena cava is found

• The left leaflet spreads back and to the left

• The fibrous sheet that makes it up generates fundamental fibers from multiple muscle fascicles and association fibers that do not lie on the same plane (Bourgery)

• The tendinous center is made of fascicles and association fibers

  • The semicircular upper band, more clearly seen on thoracic wall, the most posterior on right leaflet
  • Runs underneath and behind foramen of inferior vena cava and runs into anterior leaflet
  • The semicircular lower band, more clearly seen on abdomen, has horseshoe shape connecting right and left sheets, passing in front and laterally around vena cava

• The diaphragm is constructed from a series of digastric muscles with a tendinous center

• It is formed by two cupolas, or hemidiaphragms

  • The right is higher and can reach the 5th rib during forced expiration, receiving the right phrenic nerve
  • The left is lower and receives the left phrenic nerve

Three Main Openings in Diaphragm

• Serve to allow passage of the the thorax to the abdomen or vice versa:
  • Inferior vena cava, the aorta, and the esophagus
• Several accessory openings also exist

Foramen of the Inferior Vena Cava

• Located at the junction of medial and lateral folioles in tendinous center
• Fibrous, the largest diaphragm opening
• Irregular quadrangle, surrounded by semicircular bands of Bourgery
• At the level of the T9 vertebra
• Lets abdominal branch of right phrenic nerve pass through

Esophageal Hiatus

• Positioned in front, to the left, and above the aortic hiatus
• Borders entirely muscular and thick
• Mostly projects on left side of vertebral column at T10
• A tonic sphincter that closes the bolus alimentarius
• The two vagus nerves pass through this, the right being behind and the left being in front

Aortic Hiatus

• It is a fibromuscular hiatus
• The lateral face is built from media muscular surface of pillars
• Posterior wall is formed by vertebral bodies T11 and T12, lined with fibrous emanations
• In front, the superposition of muscle bands formed by fibers coming from medial main pillars meet at arcuate median ligament
• Behind the aorta is located the origin of thoracic duct

Other Structures That Pass Through

• Between the main pillar and medial arcuate ligament: sympathetic trunk and minor splanchnic nerve
• Lateral and over the medial arcuate ligament: the greater splanchnic nerve
• To the right, below the medial arcuate ligament: the azygos vein
• To the left, crossing the main left pillar: the hemiazygos vein
• Crossing the sternocostal triangle: the superior epigastric vessels

Thoracic Relations

• Pleuropulmonary (lateral) and mediastinal (medial) relations can be distinguished

• Relations between pleura and lungs are lined with diaphragmatic parietal pleura without interposition of connective tissue: the sheet is inseparable from diaphragm

• Diaphragm is related by circumference to the costodiaphragmatic recess of pleura

• Each cupola is related with base of the lung: bottom face middle and bottom lobes on right side; inferior face and small part of primary lobe on left side

Mediastinal Relations

• Anteriorly, the fibrous pericardium intimately adheres the diaphragm and the heart is set at tendon center through its serous fibrous wrapping
• Posteriorly, the diaphragm, nearly vertically, has anterior limit of lower mediastinum part
• Contains esophagus, thoracic duct, splanchnic nerves, thoracic sympathetic trunks and azygos veins

Arterial Supply

• The internal thoracic artery, a branch of the subclavian artery, gives rise to a collateral artery which descends along the thorax

• This collateral artery accompanies the phrenic nerve: the pericardiophrenic artery (superior diaphragmatic)

• A branch stems from inner thoracic artery where it passes the diaphragm, the Musculophrenic Artery

• This is a terminal branch going to the front and lateral muscular part of diaphragm associated with costodiaphragm recess

• The inferior phrenic artery is a collateral branch of the abdominal aorta

• Runs to the left and right via underside diaphragm slope

Venous Drainage

• Veins inverse course of arteries
• Tributaries of vena cava system
• Can anastomose with venous system in liver and esophagus

Innervation

• The diaphragm, which functions automatically, receives the phrenic nerves and the last 6 intercostal nerves