Parenchymal changes probably occur histologically in the majority of patients but are only detected on the chest radiograph in 50–70% of cases. Characteristically, parenchymal abnormalities appear as the nodal enlargement is subsiding (in lymphoma such abnormalities tend to progress in unison). The most common radiographic pattern, seen in 75–90% of patients with parenchymal opacities, is of rounded or irregular nodules 2–4 mm in diameter, which are usually well defined. Smaller or larger opacities are not uncommon, though they rarely exceed 5 mm. All zones can be affected but there is usually a mid and upper zonal predominance. The second most common pattern, seen in 10–20% of patients with parenchymal opacity, is patchy airspace consolidation. Opacities sometimes contain air bronchograms and have ill-defined margins that commonly break up into a nodular pattern. They tend to involve predominantly the peribronchovascular regions of the middle and upper lung zones, although they may be diffuse or, occasionally, have a subpleural predominance.
The parenchymal opacities described above will clear completely in about two-thirds of cases and progress to fibrosis in one-third. Permanent fibrotic shadowing is unusually coarse, with a mid and upper zone predominance. The radiographic pattern consists of coarse linear opacities with evidence of volume loss and ring shadowing caused by bullae or traction bronchiectasis. Occasionally a conglomerate opacity develops, resembling progressive massive fibrosis. Pulmonary hypertension, bullous disease with or without mycetoma formation, and pneumothorax are all recognised complications of this fibrotic stage.
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