What can cause a slight elevation in the right hemidiaphragm on chest imaging?

Causes of Slight Elevation of the Right Hemidiaphragm on Chest Imaging

The most common causes of right hemidiaphragm elevation include diaphragmatic paralysis from phrenic nerve injury, diaphragmatic eventration (congenital thinning), subdiaphragmatic pathology (hepatomegaly, subphrenic abscess, masses), and less commonly, pulmonary embolism or mediastinal tumors causing phrenic nerve dysfunction. 1

Primary Etiologies

Phrenic Nerve Dysfunction

• Phrenic nerve injury from prior procedures such as chest tube insertion or cardiac surgery is a leading cause of diaphragmatic paralysis 1
• Lung cancer with mediastinal invasion can cause phrenic nerve dysfunction, making malignancy an important consideration in the differential diagnosis 1
• Diaphragmatic paralysis manifests as absence of orthograde excursion on quiet and deep breathing, with paradoxical motion on sniffing during fluoroscopy 2

Diaphragmatic Eventration

• Complete eventration of the right hemidiaphragm is a rare congenital condition where the diaphragm is replaced by a thin fibromembranous sheet instead of normal muscle 3, 4
• Eventration represents congenital thinning of diaphragmatic muscle and manifests as focal weakness 2
• This condition is relatively uncommon in adults but should be considered when other causes are excluded 4

Subdiaphragmatic Pathology

• Subdiaphragmatic processes pushing the diaphragm upward include hepatomegaly, subphrenic abscess, hepatic masses, or other abdominal organ pathology 1
• These conditions mechanically elevate the diaphragm rather than causing intrinsic diaphragmatic dysfunction 1

Diaphragmatic Hernia

• Traumatic or non-traumatic diaphragmatic hernia can present as hemidiaphragm elevation 1
• CT findings include diaphragmatic discontinuity, "dangling diaphragm" sign, "dependent viscera" sign, and elevated abdominal organs 1
• Normal chest radiographs occur in 11-62% of cases with diaphragmatic injuries, making this diagnosis challenging 1

Other Causes

• Pulmonary embolism can present with elevated hemidiaphragm in 36% of cases, though this is a nonspecific finding 1

Diagnostic Approach

Initial Imaging Assessment

• Chest X-ray is the appropriate first-line study to identify the elevated hemidiaphragm, though it has limitations in determining the underlying cause 1
• On lateral chest radiograph, evaluate the radius of curvature or shape of the diaphragm—this is the most important factor for detecting paralysis versus eventration 5
• A ratio of HH/APD > 0.28 suggests against paralysis 5

Advanced Imaging When Indicated

• CT scan of chest and abdomen is the gold standard for definitive diagnosis when chest X-ray findings are abnormal or inconclusive, with sensitivity of 14-82% and specificity of 87% 1
• Look for specific CT signs: diaphragmatic discontinuity, segmental non-recognition of the diaphragm, "collar sign" (constriction of herniating organ at rupture level), and thickened diaphragm 1
• MRI can provide additional information when CT findings remain inconclusive, particularly for vascular assessment 1

Functional Assessment

• Fluoroscopic sniff test is a simple and effective method of diagnosing diaphragmatic dysfunction, classifying it as paralysis, weakness, or eventration 2
• Ultrasonography may be useful, especially in pregnant patients with suspected non-traumatic diaphragmatic hernia 1
• Electromyographic measurements of phrenic nerve conduction time and diaphragmatic EMG response can document abnormal diaphragmatic function, confirming 67% of radiographic suspicions 6

Critical Pitfalls to Avoid

• Do not assume a normal chest X-ray excludes significant pathology—normal radiographs occur in 11-62% of diaphragmatic injuries or uncomplicated hernias 1
• Do not overlook malignancy as a cause of diaphragmatic elevation, especially in patients with risk factors for lung cancer or mediastinal masses 1
• Avoid misdiagnosing diaphragmatic hernia as simple elevation—look for specific imaging signs such as the "collar sign" and organ herniation 1
• Do not confuse eventration with paralysis—the shape and radius of curvature on lateral chest radiograph can differentiate these conditions without requiring fluoroscopy 5
• Consider bilateral evaluation—agreement between radiographic abnormalities and functional testing is high for right-sided elevation (92%) but poor for left-sided (13%), so asymmetry assessment is crucial 6