Hilum overlay sign

Hilum overlay sign is a radiological sign used in chest radiography. It is used to differentiate whether a lung opacity is located in the mediastinum or the lung.

Overview

The hilum overlay sign is based on the principle that normal anatomy should not obscure the hilar structures. If an opacity is located within the lung, it will overlay the hilum on a frontal chest radiograph. If the opacity is located within the mediastinum, it will not overlay the hilum.

Clinical Significance

The hilum overlay sign is particularly useful in determining the location of a lung nodule or mass. This can help to narrow down the differential diagnosis and guide further management. For example, a mediastinal mass could represent a thymoma, lymphoma, or aortic aneurysm, while a lung mass could represent a lung cancer, infectious process, or granuloma.

Limitations

The hilum overlay sign is not always accurate. It can be affected by the patient's positioning, the size of the mass, and the presence of other pathology. It is also less useful in cases where the mass is large or involves both the mediastinum and the lung.

See Also

• Silhouette sign
• Air bronchogram
• Mediastinal shift

References

Hilum overlay sign Resources
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