The hilum is the area in the lungs, from where the vessels and bronchi enter..
The Radiological Hilum-
The hilum is the area in the lungs, from where the vessels and bronchi enter the lungs. But in Xray, we can find the hilum by seeing the interaction of the vessels ( the superior pulmonary vein and descending pulmonary artery).
Things to look at the pulmonary hilum-
The things that we need to see in the pulmonary hilum are –
- Position- The left hilum is higher than the right hilum or may be equal, but the right hilum is never higher than the left . Remember it is the opposite of the diaphragm( the right diaphragm is higher than left).
- Concavity- Both hila should be concave.
- Size- the size of the right descending pulmonary artery should be 16 mm in male and 15 mm in the female.
What happens if the position of hilum shifts?
The position of the hilum shifts usually in case of collapse. If the right upper lobe is collapsed, the right hilum is higher than the left side.
If the left hilum is higher than the right hilum by more than 3 mm, you may also see the left upper lobe higher than the left, by more than 3 mm.
Case of right upper lobe collapse. Note the equal position of both hila in the case.
Note the left hilum shifted upwards. Note the veil-like opacity in the left side, and tenting of left hemidiaphragm. This is a case of left upper lobe collapse. Two lines are drawn which show the difference in between the position of the hila. The upper line is drawn at the level of left hilum while lower line is drawn at the level of right hilum.
What are the causes of loss of the concavity of the hilum?
The concavity of hilum is lost and will be convex or will have opacity in the location if there is usually-
- Enlarged hilar lymph nodes.
- Hilar mass.
Note the bulge in the bilateral hila. There is also a bulge in the right paratracheal region. This is a case of sarcoidosis with bilateral hilar and right paratracheal lymphnode enlargement.
Sometimes it may be difficult to identify a large vessel from an enlarged hilar lymph node. See for example-. In such a case, you can discriminate the two by the following-
a. If the perihilar vessels converge towards the lesion, or to approximately 1 cm medial to the lesion, then the lesion is a hilar vessel, and not an enlarged lymph node or mass.
b. If the perihilar vessels don’t converge towards the lesion but are converging away from the lesion, then the opacity is a hilar lymph node or mass.