Inferior accessory fissure of the lung

Last revised by Ciléin Kearns on 30 Jan 2023

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.

Epidemiology

This accessory fissure is present in around 12% of people when examined with CT and is visible on 5-8% of frontal chest x-rays. 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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Cases and figures

  • Case 1: inferior accessory fissure
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  • Case 2: inferior accessory fissure
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  • Case 3: right inferior accessory fissure
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  • Case 4: right inferior accessory fissure
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  • Case 5: Twining's line
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  • Case 6: right inferior accessory fissure
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