What does the term infiltrate refer to in radiology?

In radiology, the term infiltrate specifically refers to any ill-defined radiodensity that suggests the presence of pathological changes within the tissue of the lung, typically indicating conditions such as pneumonia. An infiltrate appears as a cloud-like or hazy area on an X-ray or CT scan where normal anatomy may be obscured, which is indicative of disease processes such as infection, inflammation, or fluid accumulation.

The nature of the infiltrate being ill-defined is key, as it distinguishes it from other types of radiological findings, such as well-defined nodules or masses that have clear borders. This aspect of being ill-defined helps clinicians to differentiate between various diagnoses based on the appearance of the radiographs. Infiltrates often require further evaluation to identify the underlying cause.