Pulmonary infiltrate is the generic term for any blockage to an air space in a lung caused by the build-up of a substance that is foreign to the lung, according to the UBM Medica network. These substances include fluid, red, white or malignant blood cells, protein, pus and immunological substances, notes the Chinese University of Hong Kong.
The term "pulmonary infiltrate" evolved as a term for radiologists to use to describe any sort of blockage in the air space of a lung that is visible on a radiology scan, says the UBM Medica network. Causes of such blockages can include any substance foreign to the lung that accumulates gradually and eventually fills an air space. Other causes include any naturally-occurring substance in the lung that accumulates in a quantity greater than the normal amount. Pulmonary infiltrates lead to increased soft tissue density of the lung that is easily observable on a scan.
Pulmonary infiltrates are associated with conditions such as chronic pneumonia, acute respiratory distress syndrome and atelectasis, the collapse of air spaces in the lung, states The Chinese University of Hong Kong.
A persistent pulmonary infiltrate occurs as the result of an offending foreign substance lingering in the parenchyma of the lung for an extended period of time, according to BMJ. In certain cases, the conditions caused or exacerbated by pulmonary infiltrates are non-resolving.