Inferior accessory fissure of the lung

Last revised by Raymond Chieng on 30 Mar 2024

The inferior accessory fissure of the lung, also known as Twining's line, divides the medial basal bronchopulmonary segment from the rest of the lower lobe 4.


This accessory fissure is present in around 12% of people when examined with CT 3and is visible on 8% of PA chest x-rays 4. It is approximately five times more common on the right than the left.

Radiographic features

It is commonly incomplete and may only extend for 0.5-2 cm 1,3.

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