What are the potential causes of prominence of the right hilum on a chest x-ray?

Potential Causes of Right Hilum Prominence on Chest X-Ray

The most common causes of right hilar prominence are pulmonary hypertension (manifesting as enlargement of the right descending pulmonary artery), lung cancer with hilar lymphadenopathy, and infectious/inflammatory conditions including tuberculosis, sarcoidosis, and fungal infections. 1, 2, 3

Primary Vascular Causes

Pulmonary hypertension is the leading vascular cause and should be suspected when the right descending pulmonary artery measures >15 mm in women or >16 mm in men at the hilum, which has 93% sensitivity and 88% specificity for this diagnosis. 1 Additional radiographic features include:

• Main pulmonary artery enlargement >35 mm from midline to left lateral border (present in 96% of pulmonary hypertension cases) 1
• Central pulmonary artery enlargement with rapid peripheral tapering ("pruning" pattern) 4, 1
• Right heart chamber enlargement 4, 1
• Chest X-ray demonstrates 96.9% sensitivity and 99.1% specificity for moderate to severe pulmonary hypertension 1

Malignant Causes

Lung cancer represents the most concerning etiology, particularly in patients with >20 pack-year smoking history, as hilar and mediastinal lymph nodes are the most common sites of intrathoracic spread. 2 Key features include:

• Hilar mass with or without associated mediastinal widening 5, 2
• May present with superior vena cava syndrome if there is mediastinal extension 5
• Chest radiograph may show widened mediastinum or right hilar mass, though imaging can appear normal in early cases 5

Infectious and Inflammatory Causes

Tuberculosis can present as a hilar mass mimicking malignancy, with associated hilar and mediastinal lymphadenopathy, particularly in lobar pneumonia patterns involving the apical posterior segments of the upper lobe or superior segment of the lower lobe. 4, 3

Sarcoidosis uncommonly presents as unilateral hilar mass (typically bilateral hilar adenopathy is classic), but this presentation occurs and requires histological confirmation as it can demonstrate high PET-CT uptake mimicking malignancy. 2, 6, 7

Other infectious causes include:

• Histoplasmosis (can present as enlarging hilar mass) 8
• Mycoplasma pneumoniae (rare presentation with hilar lymphadenopathy and diffuse nodular shadows) 9

Diagnostic Algorithm

Measure the right descending pulmonary artery diameter at the hilum on posterior-anterior chest X-ray as the initial step to assess for pulmonary hypertension. 1 Then evaluate for:

• Cardiac enlargement, pulmonary vascular pruning, or parenchymal abnormalities 1
• Associated findings such as pleural effusion (46% in pulmonary embolism), atelectasis/infiltrate, or elevated diaphragm 4
• Amputation of hilar artery (36% in PE vs 1% in non-PE patients) 4

CT chest with IV contrast is the gold standard for definitive diagnosis when chest X-ray findings are abnormal or inconclusive, as it provides superior detection of mediastinal and hilar adenopathy and spatial localization. 1, 2 This is critical because:

• Chest radiography alone misses up to 72% of lesions 2
• CT distinguishes between vascular enlargement, lymphadenopathy, and mass lesions 1, 2
• IV contrast improves detection of vascular abnormalities and enhancing masses 2

When pulmonary hypertension is suspected based on hilar vessel enlargement, perform transthoracic Doppler echocardiography (85% sensitivity, 74% specificity for moderate to severe disease). 1

For suspected malignancy or lymphoma with accessible hilar/mediastinal nodes, proceed to endobronchial ultrasound-guided needle aspiration (EBUS-NA) for tissue diagnosis. 2

Critical Pitfalls to Avoid

Never rely on chest radiography alone when hilar prominence is identified—sensitivity is inadequate and up to 72% of lesions may be missed; proceed directly to CT imaging. 1, 2

Do not assume malignancy without histological confirmation, as benign conditions like sarcoidosis, tuberculosis, and histoplasmosis can present as hilar masses with high PET-CT uptake. 2, 6, 3, 8

Normal chest radiographs do not exclude significant pathology; if clinical suspicion persists with unexplained symptoms (dyspnea, chest pain, syncope), proceed directly to CT imaging. 1

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

Avoid ordering CT without and with contrast (dual-phase), as there is no supporting literature for this approach in hilar mass evaluation. 2