What is the differential diagnosis of right hilum enhancement on a chest x-ray?

Right Hilum Enhancement on Chest X-Ray: Differential Diagnosis

The differential diagnosis of right hilar enhancement on chest X-ray includes pulmonary hypertension with enlarged pulmonary arteries, lymphadenopathy (from malignancy, sarcoidosis, or metastatic disease), primary lung cancer, and less commonly, vascular anomalies or diaphragmatic pathology causing apparent hilar prominence.

Primary Vascular Causes

Pulmonary Hypertension

• Enlargement of the right descending pulmonary artery >15 mm in women (>16 mm in men) at the hilum is highly suggestive of pulmonary hypertension, with sensitivity of 93%, specificity of 88%, and accuracy of 92% 1
• The main pulmonary artery enlargement (>35 mm from midline to left lateral border) occurs in 96% of pulmonary hypertension cases 1
• Additional findings include central pulmonary artery enlargement with rapid tapering (pruning) and right heart chamber enlargement 1
• Chest radiography has high sensitivity (96.9%) and specificity (99.1%) for detecting moderate to severe pulmonary hypertension 1

Lymphadenopathy

Malignant Causes

• Primary lung cancer is the most common malignant cause of unilateral hilar enlargement, particularly in patients with smoking history 2
• Metastatic lymphadenopathy from occult primary tumors can present as isolated hilar masses, including squamous cell carcinoma, small cell carcinoma, and adenocarcinoma 3
• Lung cancer with mediastinal invasion can cause hilar prominence through direct extension or lymph node involvement 4

Benign Causes

• Sarcoidosis can rarely present as a unilateral hilar mass mimicking lung cancer, though bilateral hilar lymphadenopathy is more typical 2
• Castleman disease, though extremely rare at the hilum, should be considered when imaging shows characteristic enhancement patterns 5

Diagnostic Algorithm

Initial Evaluation

• Chest X-ray is the appropriate first-line imaging study, though it has limitations in determining the underlying cause 1, 4
• Measure the right descending pulmonary artery diameter at the hilum on posterior-anterior view to assess for pulmonary hypertension 1
• Evaluate for associated findings: cardiac enlargement, pulmonary vascular pruning, or parenchymal abnormalities 1

Advanced Imaging

• CT scan of the chest with contrast is the gold standard for definitive diagnosis when chest X-ray findings are abnormal or inconclusive 4, 6
• CT provides superior anatomic discrimination and can differentiate vascular enlargement from lymphadenopathy or masses 7, 8
• MRI can provide additional information when CT findings remain inconclusive, particularly for vascular assessment 1

Functional Assessment

• Transthoracic Doppler echocardiography should be performed when pulmonary hypertension is suspected, with sensitivity of 85% and specificity of 74% for moderate to severe disease 1
• PET-CT scan can help differentiate malignant from benign causes when lymphadenopathy or mass is identified 2

Critical Pitfalls to Avoid

• Do not assume all hilar enlargement represents malignancy—benign conditions like sarcoidosis can present as unilateral hilar masses requiring histological confirmation 2
• Normal chest radiographs do not exclude significant pathology; if clinical suspicion persists with unexplained symptoms, proceed directly to CT imaging 1, 4, 6
• Chest X-ray is insensitive for mild pulmonary hypertension; further evaluation with echocardiography is warranted when symptoms suggest elevated pulmonary pressures despite normal-appearing hilar vessels 1
• Always obtain tissue diagnosis before assuming lung cancer, as histological examination is required for definitive diagnosis 2, 3
• Consider patient risk factors: smoking history increases likelihood of malignancy, while systemic symptoms may suggest sarcoidosis or other inflammatory conditions 2