Further reading:

https://doi.org/10.3390/diagnostics13203171

<aside>

The Hilum Overlay Sign is a chest radiographic sign used to determine whether a mediastinal or hilar mass is anterior, posterior, or arising from the hilum.

</aside>

It helps assess whether pulmonary hilar structures (e.g., pulmonary vessels, bronchi) are visible through a mediastinal opacity.

![a. PA CXR demonstrates a well demarcated rounded opacity along the right parahilar region of the right lung field with hilar vessels visible within the opacity, consistent with hilum overlay sign, indicating that the mass is either anterior or posterior to the hilum. b, c. HRCT one week later confirms the finding by demonstrating a lobulated soft-tissue mass lesion in the superior segment of the right lower lobe, just posterior to the right hilum.

Case courtesy Dr Nabarun Das, MD, Dr Marrie Pegu & Dr Supriya Paul // #SMCHCase ](attachment:077070ed-5d45-45b9-a1b8-cbe8f3a9c487:HOS1.webp)

a. PA CXR demonstrates a well demarcated rounded opacity along the right parahilar region of the right lung field with hilar vessels visible within the opacity, consistent with hilum overlay sign, indicating that the mass is either anterior or posterior to the hilum. b, c. HRCT one week later confirms the finding by demonstrating a lobulated soft-tissue mass lesion in the superior segment of the right lower lobe, just posterior to the right hilum.

Case courtesy Dr Nabarun Das, MD, Dr Marrie Pegu & Dr Supriya Paul // #SMCHCase

![Hilum overlay sign. Chest radiograph PA view (A) shows well-marginated mass over right hilum (arrowheads). Hilar vessels (arrow) are seen through the mass, suggesting the mass is either anterior or posterior to the hilum. Chest radiograph lateral view (B) confirms the anterior location of the mass (arrowheads).

Ahuja J, Strange CD, Agrawal R, Erasmus LT, Truong MT. Approach to Imaging of Mediastinal Masses. Diagnostics. 2023; 13(20):3171. https://doi.org/10.3390/diagnostics13203171](https://prod-files-secure.s3.us-west-2.amazonaws.com/2aa05644-4658-4c26-84d3-64c36b55fb6c/fd1ead49-30e8-45a8-a200-30d9830a095f/diagnostics-13-03171-g002.webp)

Hilum overlay sign. Chest radiograph PA view (A) shows well-marginated mass over right hilum (arrowheads). Hilar vessels (arrow) are seen through the mass, suggesting the mass is either anterior or posterior to the hilum. Chest radiograph lateral view (B) confirms the anterior location of the mass (arrowheads).

Ahuja J, Strange CD, Agrawal R, Erasmus LT, Truong MT. Approach to Imaging of Mediastinal Masses. Diagnostics. 2023; 13(20):3171. https://doi.org/10.3390/diagnostics13203171

Principle

If pulmonary vessels and bronchi of the hilum are clearly seen through the mass, the mass is not located in the hilum.
Therefore, the mass must lie either anterior or posterior to the hilum.
If the hilar structures are obscured, the mass is likely arising from or involving the hilum.

Application

Visibility of Hilum	Interpretation
Hilum clearly visible through the opacity	Mass is not hilar (anterior or posterior to hilum)
Hilum obscured	Mass is hilar in origin

This is most often used to differentiate:

Mediastinal masses vs. hilar masses
Lymphadenopathy vs. vascular structures

Clinical Examples

Scenario	Likely Diagnosis
Right paratracheal mass with visible right pulmonary artery	Anterior mediastinal mass (e.g., thymoma, thyroid mass)
Homogeneous opacity obscuring right pulmonary artery	Hilar mass (e.g., bronchogenic carcinoma, lymphadenopathy)

Principle

Application

Related Signs