Transfissural pulmonary diseases occur when a pathological process extends from one lobe via an interlobar fissure into an adjacent lobe ¹. The finding is most commonly due to primary malignancy; however, some infections are known to do so.

Terminology

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

Pathology

There is an ongoing debate about whether a tumor that crosses a fissure should be upstaged. 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.

Differential diagnosis

• infection

  • tuberculosis

  • actinomycosis

  • nocardiosis

  • Streptococcus anginosus ²

  • blastomycosis

  • mucormycosis

• malignancy: tumor infiltration of the lung fissures has been described for many lung cancers and lymphoma ^1,2

​Practical points

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.