So-called inflammatory myofibroblastic tumour: a proliferative lesion of fibroblastic reticulum cells?

The term inflammatory pseudotumour was originally used in a generic fashion for any lesion which simulated a neoplastic condition at a clinical, macroscopic and microscopic level but which was thought to have an inflammatory/reactive pathogenesis. In more recent times, the term has been employed in a more restrictive sense for a mass lesion characterized microscopically by the proliferation of a spindle cell component against a heavy inflammatory infiltrate of mixed composition but usually with a predominance of mature lymphocyte and plasma cells. The spindle cell component has generally been regarded as being of mesenchymal nature and having morphological and phenotypical features consistent with fibroblasts or myofibroblasts, the latter cell being clearly preferred over the former in the more resent reports. The term inflammatory myofibroblastic tumour (IMFT) is the one currently favoured, which proposes the myofibroblastic nature of the process. It is the purpose of this review to bring forth some evidence that the neoplastic spindle cell component of IMFT may be instead derived from the subtype of cells of the accessory immune system that have been variously called fibroblastic reticulum cells, myoid cells, and dictyocytes.