What does a scalloped hemidiaphragm (half of the diaphragm) on an X-ray (X-ray computed tomography) indicate?

Scalloped Hemidiaphragm on X-ray

A "scalloped" hemidiaphragm appearance on chest X-ray typically indicates an abnormally elevated diaphragm with an irregular, wavy contour rather than the normal smooth dome shape, suggesting either diaphragmatic eventration, paralysis, or underlying pathology causing diaphragmatic elevation.

Radiographic Appearance and Significance

The scalloped or irregular contour of an elevated hemidiaphragm differs from the normal smooth dome configuration and warrants further investigation to determine the underlying cause 1.

Key distinguishing features on chest X-ray include:

• Shape assessment: The radius of curvature on lateral chest radiograph is the most important factor for detecting diaphragmatic paralysis versus eventration 1
• Eventration typically shows a smooth but elevated contour without paradoxical motion, while paralysis may show a more irregular or scalloped appearance 2, 1
• Suspicious findings include abnormal lucency, soft tissue opacity with mediastinal deviation, or hemidiaphragm elevation 3

Differential Diagnosis

The scalloped/elevated hemidiaphragm can indicate:

• Diaphragmatic eventration: Abnormal elevation where the diaphragm is replaced by a thin fibromembranous sheet instead of normal muscle 4, 5
• Diaphragmatic paralysis: Results from phrenic nerve injury (from prior chest procedures, cardiac surgery) or lung cancer with mediastinal invasion 3
• Diaphragmatic hernia: Traumatic or non-traumatic herniation of abdominal contents into the thorax 6, 3
• Subpulmonic effusion: Can mimic elevated diaphragm with lateral peaking and steep lateral slope 6
• Subdiaphragmatic pathology: Masses or processes pushing the diaphragm upward 3

Diagnostic Algorithm

Initial imaging approach:

1. Chest X-ray (PA and lateral) is the appropriate first diagnostic study to identify the elevated hemidiaphragm 6, 3
2. Fluoroscopy provides more accurate assessment of diaphragmatic motion and can differentiate eventration (no paradoxical motion) from paralysis (paradoxical motion present) 6, 4, 2
3. CT scan with IV contrast is the gold standard when hernia or other structural pathology is suspected, with 14-82% sensitivity and 87% specificity 6, 3, 7

Specific CT findings to evaluate:

• Diaphragmatic discontinuity or segmental non-recognition 6
• "Dangling diaphragm" sign (free edge curling toward abdomen) 6
• "Dependent viscera" sign (organs abutting chest wall) 6
• "Collar sign" (constriction of herniated organ at rupture level) 6, 3
• Elevated abdominal organs or thickened diaphragm 6

Ultrasound can assess diaphragmatic excursion, thickness, and identify paradoxical movement with high sensitivity and specificity for neuromuscular disorders 6

Clinical Pitfalls to Avoid

Critical diagnostic errors:

• Don't assume benign elevation: Normal chest radiographs occur in 11-62% of diaphragmatic injuries or uncomplicated hernias 6, 3
• Don't overlook malignancy: Lung cancer with mediastinal invasion can cause phrenic nerve dysfunction and diaphragmatic elevation 3
• Don't confuse subpulmonic effusion: This shows lateral peaking with steep lateral slope and gradual medial slope, requiring lateral decubitus views or ultrasound for differentiation 6
• Don't rely solely on chest X-ray: Initial radiographic findings are misinterpreted in approximately 25% of cases 6

Management Considerations

Symptomatic patients require intervention:

• Diaphragmatic plication is indicated for all symptomatic patients with elevated diaphragm regardless of etiology (eventration or paralysis) 2, 8
• Surgery restores normal pulmonary parenchymal volume and eliminates paradoxical motion 4, 2
• For diaphragmatic hernia, laparoscopic repair is strongly recommended in stable patients 6, 3

Asymptomatic patients with incidentally discovered elevated diaphragm can be managed conservatively with observation 4, 8