Extrapulmonary hyalinizing granuloma: a rare case with intra-articular and tenosynovial involvement.

Extrapulmonary hyalinizing granuloma (EPHG) is a notably rare condition, representing an exaggerated chronic immune response to antigenic stimuli. This report presents the first documented case of intra-articular and tenosynovial EPHG with radiological evaluation and pathological confirmation in a 60-year-old man presenting with wrist pain and swelling. Imaging findings were relatively symmetric with marked distension of the distal radioulnar joints and extensor tendon sheaths with masses and nodules of various sizes surrounded by synovitis and accompanied by bony erosions. On US, the masses were heterogeneous but mostly hypo- to iso-echoic compared to muscle and relatively hypovascular. On MRI, compared to muscle, the nodules exhibited iso-intense signal on T1-weighted images, iso- to mildly hyper-intense signal on T2-weighted fat-suppressed images, and minimal enhancement on post-contrast images. The diagnosis of EPHG was revealed through biopsy and pathologic examination with glucocorticoids being effective in treatment.