Review Article: "Mesenchymal Tumor" or "Decidual-Like Reaction"?

Abstract

For more than 40 yr, an unusual urinary bladder lesion has been known to occur in certain strains of mice, but no consensus has been obtained regarding its etiology, pathogenesis, biology, or classification. The lesion was first assumed to be epithelial and nonneoplastic, then it was called a smooth muscle cell tumor or leiomyosarcoma because of ultrastructural characteristics for smooth muscle cells. Later, the nonspecific term "mesenchymal tumor" was introduced due to histomorphologic differences from all smooth muscle tumors known. Recently, a proposal was made to name it "decidual-like reaction" because of the histomorphologic similarity to the rare spontaneous decidual reaction in the uterus of aging mice. Both

Proliferative and Nonproliferative Lesions of the Rat and Mouse Male Reproductive System

“…Comments: The definitive nature of this lesion is still under debate (Karbe 1999). One view regards the lesion as a benign tumor based on the potential to be locally invasive.…”

“…It differs somewhat from that of the ventral prostate: the lesion is less uniform and is characterized by small acini with a single layer of atypical cuboidal to somewhat flat cells with pale cytoplasm and hypochromatic nuclei, the cellular polarity is often disturbed and no sign of secretory activity is seen, some necrosis and thickening of periacinar fibromuscular tissue is often found. (Karbe 1999). One view regards the lesion as a benign tumor based on the potential to be locally invasive.…”

Urinary Tract

“…The subepithelial capillary plexus may be the site of vascular proliferative changes. 497,498 Since a report by Bonsor and Jull in 1956, these lesions have been described following implantation of foreign bodies and administration of chemicals under names such as vegetative changes and leiomyosarcoma. 497,498 Since a report by Bonsor and Jull in 1956, these lesions have been described following implantation of foreign bodies and administration of chemicals under names such as vegetative changes and leiomyosarcoma.…”

“…498 Given the diverse and bizarre histological appearances of many non-neoplastic lesions of mesenchymal tissues in human pathology, it would not be surprising if these lesions were non-neoplastic in nature. 498 Given the diverse and bizarre histological appearances of many non-neoplastic lesions of mesenchymal tissues in human pathology, it would not be surprising if these lesions were non-neoplastic in nature.…”

Histopathological and Immunohistochemical Characterization of Spontaneously Occurring Uterine Deciduomas in Young Adult Rats

“…Hyperplastic lesions of decidual stromal cells, so-called decidual reactions/decidual tumors, have been found in the uterus or subserosal abdominal locations in rats 1 , 2 , mice 3 , 4 , guinea pigs 5 , rabbits 6 , dogs 7 , monkeys 8 , and humans 9 , 10 . These lesions are characterized by focally extensive areas of hyperplastic and hypertrophied eosinophilic, round, oval to somewhat elongated cells, which are thought to be endometrial stromal cells.…”