What is the location of the right hilar and right infrahilar regions in the lung?

Anatomical Location of Right Hilar and Right Infrahilar Regions

The right hilar region is located at the medial aspect of the right lung where the main bronchus, pulmonary artery, and pulmonary veins enter and exit the lung, while the right infrahilar region lies immediately below the hilum extending toward the lower lobe structures.

Right Hilar Anatomy

The right hilum is positioned slightly lower and more anteriorly placed than the left hilum on the mediastinal surface of the lung 1. The hilar zone encompasses lymph node stations 10 and 11 according to the IASLC staging system 2.

Key Vascular Structures at Right Hilum

• The right hilar shadow relates primarily to the ascending and descending pulmonary arteries and the right superior pulmonary vein 3
• The right pulmonary artery bifurcates within the mediastinum before reaching the hilum, creating two distinct vascular converging points visible on chest radiographs 4
• The upper converging point is formed by right upper lobe arterial branches 4
• The lower converging point consists of the right descending pulmonary artery, superior pulmonary vein crossing it, middle lobe artery, and superior segmental artery of the lower lobe 4
• These two converging points can be distinguished in 95% of chest radiographs, with the upper point situated above the single left hilar converging point in 83% of cases 4

Bronchial Anatomy

• The right main bronchus enters the hilum and divides into lobar bronchi 1
• Anatomical variations occur in 16.1% of right lungs, with variations in bronchial number and arrangement 5

Right Infrahilar Region

The infrahilar region extends from the lower border of the hilum downward toward the basal segments of the right lower lobe 2.

Anatomical Boundaries

• The subcarinal zone (station 7) extends down to the level of origin of the right middle lobe bronchus, marking the superior boundary of the infrahilar region 2
• The lower zone encompasses lymph node stations 8 and 9 2
• The right inferior pulmonary vein lies behind the lower hilum and contributes minimally to normal hilar density, with its horizontal course distinguishing it from vertically oriented lower lobe arteries 3

Clinical Significance

Pathologic Considerations

• Soft tissue attenuation in the right hilar and infrahilar regions most frequently represents lung cancer with hilar/mediastinal lymph node metastases, as hilar and mediastinal lymph nodes are the most common sites of intrathoracic spread 2, 6
• Bulky hilar adenopathy can cause extrinsic airway compression with resultant airway symptoms 2, 6
• Recurrent pneumonia in the same anatomic distribution or relapsing COPD exacerbations should raise concern for underlying neoplasm causing postobstructive changes 2, 6

Diagnostic Imaging

• Contrast-enhanced chest CT is essential to characterize soft tissue attenuation, distinguish lymph nodes from vascular structures, and assess mediastinal extension 6
• Conventional tomography in anteroposterior, 55-degree posterior oblique, and lateral projections provides complete hilar assessment 3
• Finding only one converging point on the right (instead of the normal two) suggests collapse of either the upper or lower lobe, whereas visualization of both points excludes major atelectasis 4

Common Pitfalls

• Anatomical variations are extremely common, occurring in 59.18% of right lungs, with variations in pulmonary artery and vein being most frequent (36.73% each) 1
• The right superior pulmonary vein is intimately associated with and inseparable from the arteries, making identification challenging 3
• Prominence of both superior and inferior pulmonary veins may cause hilar pseudotumors 3
• Even when a tumor mass in the pulmonary hilum is highly suggestive of lung cancer, positive diagnosis requires histological examination, as benign conditions like sarcoidosis can present identically 7