What is indicated by cavity formation in a radiological diagnosis?

Cavity formation in a radiological diagnosis typically indicates the presence of necrotic tissue within the lungs, which is a hallmark of specific pathologies. Tuberculosis is characterized by the development of cavitary lesions as it progresses, notably within lung tissues where the bacteria create areas of caseous necrosis. These cavities appear on radiological imaging as spaces or "holes" resulting from the destruction of lung tissue due to the inflammatory response to the infection.

In the context of the other options, atelectasis pertains to the collapse of lung tissue and does not lead to cavity formation. Pulmonary edema involves excess fluid in the lungs and primarily presents with consolidations or "whitened" areas on imaging rather than cavitations. A pulmonary embolus refers to a blockage in the pulmonary arteries, which may show signs of infarction but does not result in cavitary changes. Therefore, the indication of cavities specifically aligns with the pathological process seen in tuberculosis, confirming this choice as the correct answer.