Left Hemidiaphragm: Anatomy and Clinical Significance
The left hemidiaphragm is the portion of the diaphragm muscle located on the left side of the body, separating the left thoracic cavity from the abdominal cavity, and is more commonly affected by traumatic and congenital hernias than the right side due to the absence of the protective effect of the liver. 1
Anatomical Structure and Function
The diaphragm is a dome-shaped musculoaponeurotic structure that serves as:
- The primary muscle of respiration
- A separator between thoracic and abdominal cavities
- A contributor to gastroesophageal junction competence
The diaphragm consists of two distinct hemidiaphragms (left and right) that have some important differences:
- The left hemidiaphragm is typically positioned lower than the right hemidiaphragm due to the presence of the liver on the right side
- The left hemidiaphragm has openings for the esophagus and aorta
- It is more susceptible to herniation due to less protection compared to the right side
Clinical Significance of the Left Hemidiaphragm
Vulnerability to Injury and Herniation
The left hemidiaphragm is more frequently affected by both traumatic and congenital hernias:
- 50-80% of diaphragmatic hernias after blunt trauma affect the left hemidiaphragm 1
- 85% of Bochdalek hernias (most common congenital diaphragmatic hernia) occur on the left side 1
- This vulnerability is attributed to the protective effect of the liver on the right side, which reduces traumatic force 1
Diagnostic Imaging
When evaluating the left hemidiaphragm, several imaging modalities are used:
- Chest X-ray (anteroposterior and lateral): First-line imaging with sensitivity of 2-60% for left-sided hernias 2
- CT scan with IV contrast: Gold standard with sensitivity of 14-82% and specificity of 87% 2
- Ultrasound: Valuable for bedside assessment, particularly in immobile patients or those in intensive care 3
- Fluoroscopy: Primarily used for evaluating diaphragmatic motion 4
Diagnostic Signs of Left Hemidiaphragm Abnormalities
Key radiographic findings suggesting left hemidiaphragm pathology include:
- "Dangling diaphragm" sign
- "Dependent viscera" sign
- "Collar sign"
- Intrathoracic herniation of abdominal contents
- Forward displacement of gastric bubble
- Missing gastric folds 2
Common Pathologies Affecting the Left Hemidiaphragm
Traumatic Diaphragmatic Hernias
- More common on the left side (50-80% of cases) 1
- Caused by blunt trauma (e.g., road traffic collisions) or penetrating injuries
- Can present acutely or have delayed presentation years after injury
- Symptoms include dyspnea (86%) and abdominal pain (17%) 1
Congenital Diaphragmatic Hernias
- Bochdalek hernia: Most common type (95% of congenital hernias), predominantly affects the left posterior diaphragm (85%) 1
- Can remain asymptomatic until adulthood, with an incidence of 0.17% in adults 1
- May present with gastrointestinal and respiratory symptoms
Elevation or Paralysis
- Can result from phrenic nerve injury, stroke, or thoracic/abdominal surgery
- Ultrasound is particularly valuable for diagnosis and follow-up of paresis or paralysis 3
Clinical Pitfalls and Caveats
Delayed diagnosis is common: 5-45% of diaphragmatic hernias have delayed diagnosis 1
Right-sided injuries are more lethal: Although left-sided injuries are more common in hospitalized patients, right-sided injuries are more common in autopsy findings, suggesting higher mortality 1
Negative CT does not rule out pathology: CT scan has a sensitivity of only approximately 64% for internal hernias 2
Intermittent herniation may be missed on static imaging, making dynamic studies important in some cases 2
Misdiagnosis as pneumonia or bronchiolitis can occur, especially following viral illness with respiratory distress 1
The left hemidiaphragm's unique anatomical position and vulnerability to injury make it an important structure to evaluate in trauma patients and those with unexplained respiratory or gastrointestinal symptoms.