Progressive massive fibrosis

Progressive massive fibrosis (PMF) refers to the formation of large mass-like conglomerates, predominantly in the upper pulmonary lobes, associated with radiating strands. These classically develop in the context of certain pneumoconioses (especially coal worker's pneumoconiosis and silicosis) although similar mass-like densities have occasionally been described with talcosis.

Radiographic features

Plain radiograph

May be seen as large symmetric bilateral opacities with irregular margins in the upper lobes ³.

CT

Mass-like areas of lung opacification associated with radiating strands are seen; the "sausage-shaped" mass is characteristic. These regions commonly contain air bronchograms and calcifications ⁴. These areas can shrink over time and migrate towards the hilar regions ⁵.

MRI

Magnetic resonance imaging can be helpful for distinguishing between progressive massive fibrosis and lung cancer ³. The latter typically appears as T2-bright, whereas progressive massive fibrosis appears as T2-dark (compared to skeletal muscle) ³.

The most frequent MRI appearance are regions which have following signal characteristics ^1,2:

• T1: iso- to hyperintense
• T2:
  • hypointense (compared with skeletal muscle)
  • areas of internal high T2 signal
  • there may be rim enhancement

Nuclear medicine

On PET-CT, progressive massive fibrosis can be FDG-avid ³.

Differential diagnosis

Possible differential considerations include:

• pulmonary talc granulomatosis
• sarcoidosis
• lung cancer: has a higher SUVmax on PET-CT ⁷

In some situations consider pulmonary manifestations of sarcoidosis.