PSEUDOSARCOMATOUS MYOFIBROBLASTIC TUMOR OF THE URINARY-BLADDER IN CHILDREN - A STUDY OF 11 CASES WITH REVIEW OF THE LITERATURE - AN INTERGROUP RHABDOMYOSARCOMA STUDY

Pseudosarcomatous myofibroblastic tumor (PMT) is the result of reactiv e proliferation of myofibroblasts. In children, PMT of the urinary bla dder can be mistaken for embryonal rhabdomyosarcoma clinically, radiol ogically, and by light microscopy. We are reporting the clinical, hist ological, and immunohistological features of 11 patients with childhoo d PMT of urinary bladder that were diagnosed initially as a sarcoma, u sually rhabdomyosarcoma. The morphologic spectrum of PMT is broad, wit h mixtures of myxoid, leiomyomatous, and sclerosing matrix patterns, t he myxoid type being the most common. The proliferating cells consist of three forms of myofibroblastic cells: long spindle cells (type I), intermediate spindle cells (type II), and ganglion-like cells (type II I), together with various types of inflammatory cells. The immunohisto logic profile of the proliferating cells was characterized by positive reactions to vimentin, muscle-specific actin, ct-smooth-muscle actin, polyclonal desmin, and keratin. Ultrastructural studies showed myofib roblastic differentiation of the tumor cells. No patients have had met astases or local recurrence. Histologic, immunohistochemical, and clin ical data from 71 cases of PMT, including the 11 cases in this report, confirm the benign behavior of these lesions. The etiology of these l esions is unclear, including the absence of surgical or other trauma i n all of the children.