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Topic

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Diaphragm

The diaphragm is a dome-shaped musculotendinous partition separating the thoracic and abdominal cavities. It plays a vital role in respiration, contracting and flattening during inspiration to increase thoracic volume and relaxing during expiration. The diaphragm has a central tendon where its muscle fibers converge and three major openings: the caval opening (T8), the esophageal hiatus (T10), and the aortic hiatus (T12). Its muscular parts include the sternal part (arising from xiphoid process), costal part (from lower six ribs), and lumbar part (arising from crura attached to lumbar vertebrae).

Synonyms

  • Thoracoabdominal diaphragm

  • Respiratory diaphragm

  • Phrenic diaphragm

Function

  • Principal muscle of inspiration: contracts and flattens to expand thoracic cavity

  • Aids in expiration by passive relaxation

  • Contributes to intra-abdominal pressure regulation (defecation, urination, childbirth)

  • Serves as a barrier between thoracic and abdominal cavities

  • Provides hiatuses for passage of great vessels and esophagus

Arterial Supply

  • Superior surface: pericardiacophrenic and musculophrenic arteries (branches of internal thoracic artery), superior phrenic arteries (branches of thoracic aorta)

  • Inferior surface: inferior phrenic arteries (branches of abdominal aorta)

Venous Drainage

  • Superior surface: pericardiacophrenic and musculophrenic veins → internal thoracic vein; superior phrenic veins → azygos and hemiazygos veins

  • Inferior surface: inferior phrenic veins → inferior vena cava or left renal vein

Nerve Supply

  • Motor innervation: phrenic nerve (C3–C5) — “C3, 4, 5 keep the diaphragm alive”

  • Sensory innervation: phrenic nerve (central portion), intercostal nerves (T5–T11) and subcostal nerve (T12) (peripheral portions)

MRI Appearance

T1-weighted images:

  • Diaphragm appears as a low signal intensity muscular structure separating thoracic and abdominal cavities

  • Central tendon is very low signal (fibrous tissue)

  • Useful for identifying diaphragmatic continuity and defects

T2-weighted images:

  • Muscle remains low to intermediate signal, adjacent fat and abdominal contents provide contrast

  • Pathology (edema, inflammation, tumors) may appear as hyperintense areas within the muscle

STIR (Short Tau Inversion Recovery):

  • Fat suppression increases visibility of edema, inflammatory, or infiltrative changes

  • Normal diaphragm stays low signal, whereas pathology shows hyperintensity

T1 Post-Contrast (Gadolinium-enhanced):

  • Normal diaphragm enhances mildly and homogeneously

  • Defects, tumors, or inflammatory processes enhance irregularly or asymmetrically

CT Appearance

Non-contrast CT:

  • Diaphragm appears as a thin muscular sheet between thoracic and abdominal cavities

  • Best visualized with lung and soft tissue windows

  • Hernias or defects are seen as abdominal contents extending into thoracic cavity

Contrast-enhanced CT (CECT):

  • Provides clear definition of diaphragmatic margins

  • Excellent for detecting trauma (rupture), congenital defects, tumors, or abnormal vascularization

  • Multiplanar reformats (coronal, sagittal) are particularly useful for assessing integrity

MRI images

Diaphragm anatomy MRI AXIAL image -img-00000-00000

MRI images

Diaphragm anatomy MRI coronal image -img-00000-00000

CT image

Diaphragm anatomy CT axial image -img-00000-00000