Hilum Fat: Anatomy and Clinical Significance

The hilum is the medial indentation on each lung where bronchi, pulmonary vessels, nerves, and lymphatics enter/exit. Hilum fat is the peribronchovascular adipose tissue surrounding these structures, continuous with mediastinal fat.

Imaging Relevance

• On CT, hilum fat appears as low-attenuation tissue around hilar vessels/bronchi.
• Loss of hilum fat planes suggests pathology: hilar mass, lymphadenopathy, fibrosis, or post-radiation changes.
• Enlarged hilar nodes displace or efface hilum fat.

Clinical Context

Hilum fat is a normal landmark; its preservation or obliteration aids radiologists in assessing hilar pathology (lung cancer, sarcoidosis, TB, lymphoma). It is not a distinct anatomical compartment but a radiological sign.