The term pulmonary infiltrate is considered a context-dependent, non-specific and imprecise descriptive term when used in radiology reports (plain film or CT).
From a pathophysiological perspective, the term "infiltrate" refers to “an abnormal substance that accumulates gradually within cells or body tissues” or “any substance or type of cell that occurs within or spreads as through the interstices (interstitium and/or alveoli) of the lung, that is foreign to the lung, or that accumulates in greater than normal quantity within it” ref.
While when used with a better anatomic reference, such as alveolar, air space, interstitial, or nodular, it may occasionally be helpful in suggesting an underlying pathologic basis for the findings on the radiograph, the use of the term in general is discouraged.
According to a study by Patterson et al, the use of the term "infiltrate" on its own was not shown to be very meaningful for the clinician or very beneficial to the patient 1.
According to Fleischner Society recommendations, use of the term "infiltrate" remains controversial and is no longer recommended 3.