Cryptogenic organising pneumonia.

Organising pneumonia is defined histopathologically by intra-alveolar buds of granulation tissue, consisting of intermixed myofibroblasts and connective tissue. Although nonspecific, this histopathological pattern, together with characteristic clinical and imaging features, defines cryptogenic organising pneumonia when no cause or peculiar underlying context is found. Rapid clinical and imaging improvement is obtained with corticosteroid treatment, but relapses are common after stopping treatment.