Inflammatory pseudotumour of soft tissues: a clinicopathological and immunohistochemical analysis of 18 cases.

Pseudosarcomatous proliferation of myofibroblasts, fibroblasts and inflammatory cells have been reported in a wide variety of sites and are most commonly termed inflammatory pseudotumours. Despite increasing recognition, the occurrence of inflammatory pseudotumour in somatic soft tissue is poorly documented, such that these lesions are commonly mistaken for a variety of benign and malignant neoplasms. This report documents our experience of 18 cases of soft tissue inflammatory pseudotumour. All arose in adults (median age 54.5 years; range 28-83 years) and showed no sex predilection. Anatomical location was varied but the head and neck region and abdominal cavity were most common. They displayed a spectrum of histological appearances but all were characterized, to a greater or lesser extent, by an admixture of myofibroblasts and fibroblasts, most commonly arranged in short interwoven fascicles, together with a polymorphic inflammatory cell component, consisting principally of lymphocytes and plasma cells. In some cases xanthoma cells were prominent. Simple surgical excision appeared to be curative. The importance of recognizing the presence of a wide clinicopathological spectrum is emphasized and the differential diagnosis, especially from fibrohistiocytic neoplasms or Hodgkin's disease, is discussed.