Mesenchymal proliferation with decidual-like morphology in seminal vesicles of aging mice

Lesions characterized by spindle and epithelioid cells and nuclear progeste rone receptors are described in seminal vesicles of four aging mice. The le sions of two mice also contain granular metrial gland (GMG)-like cells. The same cellular details are seen in the uterine decidual reaction and the si milar urinary bladder lesion in mice, also called mesenchymal tumor. Theref ore, it is hypothesized that these lesions in male accessory sex glands and the urinary bladders of aging male and female mice are of mesenchymal orig in with the potential for differentiation along several pathways, leading e specially to lesions with decidual-like morphology, but also to lesions whi ch contain only spindle cells. The decidual hypothesis is further supported by the occurrence of round eosinophilic granules and focal necrosis, inter preted as a sign of regression in all these lesion types. The bilateral les ions of a fifth mouse consist of spindle cells and scar-like tissue, the la tter suggesting regression, and lack epithelioid and GMG-like cells. In thi s case, verification of the diagnosis depends on the demonstration of proge sterone receptors, absent in normal glands. Uterine decidual reactions during pregnancy are brought about by priming wi th progesterone/estrogen, initiation through the blastocyst, and maintenanc e through progesterone. Experiments by others show that priming may also oc cur through growth factors/growth hormone, initiation through prostaglandin s, and maintenance through testosterone in mice. It is hypothesized that up on such stimulation, certain cells in male accessory sex glands and the uri nary bladder, possibly derived from the Muellerian ducts or other subperito neal tissue, appear to have the potential in mice of developing into spindl e and epithelioid cells, including decidual-like cells. All published uterine decidual reactions and lesions with decidual-like mor phology in other organs of mice stayed within the peritoneal coverage of th eir respective organ and did not metastasize despite their "anaplastic", tu mor-like appearance. Thus, they should be considered non-neoplastic. It is proposed to name above lesions in male accessory sex glands and urina ry bladders "mesenchymal proliferation, decidual type" or "mesenchymal prol iferation, spindle-cell type", depending on their cellular characteristics.