RALS

Mnemonic

RALS, for the position of the pulmonary artery relative to the bronchus at each hilum:

• RA - on the Right, the artery is Anterior
• LS - on the Left, the artery is Superior

This is the reliable way to identify left from right lung on imaging and in the dissecting room, and it follows from the left main bronchus passing under the aortic arch while the right does not.

The other hilar rule is that on both sides the veins are the most anterior and inferior structures.

Expansion

• Right pulmonary artery is Anterior to the bronchus.
• Left pulmonary artery is Superior to the bronchus.