Traversal of lung fissures

Last revised by Daniel J Bell on 30 Nov 2021

Only a small number of pulmonary diseases are known to directly traverse the lung fissures such that the lung pathology extends from one lobe via the interlobar fissure into an adjacent lobe 1. The finding is most commonly due to primary malignancy, however, some infections are also known to do so.

A bulging fissure is different as this entity is due to mass effect on the fissure but there is no suggestion that the pathology in question has traversed the fissure so that it is now in two adjacent lobes.

There is an ongoing debate about whether a tumor that crosses a fissure should be upstaged. Currently the TNM staging system for lung cancer does not account for tumors crossing from one lobe of the lung into another. Evidence suggests that if a tumor can cross a complete fissure it is likely more aggressive as it needs to traverse two layers of visceral pleura to do this. The PL grading system tries to account for this. The ninth edition of the TNM staging system for lung cancer is expected in 2024 3-6.

Occasionally the synchronous presence of opacity in two adjacent lobes may incorrectly lead to the presumption that the pathology directly crossed through a fissure but in fact, the infection/malignancy reached both lobes through normal routes, most commonly the airways.

Occasionally due to absence of part or all of an interlobar fissure, a lung pathology will be erroneously assumed to have crossed a fissure, when no such infiltration actually occurred. 

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