Bulging fissure sign | Radiology Signs

Answer:

The bulging fissure sign represents expansive lobar consolidation causing fissural bulging or displacement by copious amounts of inflammatory exudate within the affected lung parenchyma. It is classically associated with right upper lobe consolidation due to Klebsiella pneumoniae infection, though it can occur with any form of pneumonia. The sign indicates an aggressive lobar bacterial pneumonia, often with lung necrosis. Other pathogens associated with this sign include Streptococcus pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Legionella pneumophila, Yersinia pestis, and Mycobacterium tuberculosis. Beyond infectious causes, the bulging fissure sign can also result from any space-occupying process in the lung such as pulmonary hemorrhage, lung abscess, or malignant infiltration including bronchoalveolar carcinoma. The prevalence of this sign has been decreasing due to prompt administration of antibiotic therapy in suspected pneumonia cases. It is also less commonly detected in hospital-acquired Klebsiella pneumonia compared to community-acquired infections.

Why is it called so?:

The sign is named for the characteristic bulging or outward displacement of the pulmonary fissure on imaging. The fissure, which normally appears as a thin linear structure separating lung lobes, becomes displaced outward or anteriorly due to the expanding consolidation in the adjacent lobe, creating the appearance of a bulge.

Pathophysiology:

The bulging fissure sign develops through the following mechanism: an aggressive bacterial infection or space-occupying lesion causes intense inflammatory response within a lung lobe. This results in the production of large volumes of exudative fluid and inflammatory material that accumulates within the consolidated lobe. The accumulated exudate causes the affected lobe to expand beyond its normal boundaries. This lobar enlargement exerts outward pressure on the adjacent pulmonary fissure, causing it to bow or bulge outward from its normal position. The degree of bulging correlates with the volume of exudate and the aggressiveness of the inflammatory process. On frontal chest radiographs, the fissure below an enlarged consolidated lobe bulges downward, while on CT imaging, the fissure appears displaced posteriorly or laterally depending on location and severity.

Alternative names:

No alternative names exist for this sign.

Other associated named signs:

Other classical thoracic radiology signs associated with pneumonic consolidation and related pathology include the air crescent sign, Fleishner sign (related to pulmonary embolism), and the juxtaphrenic sign (seen in lobar collapse).