The objective of this study was to re-examine the histogenesis of adenomato
id tumors. This benign neoplasm is characterized by gland-like structures w
ith a pseudodinfiltrative pattern, usually involving fibromuscular tissue a
t a certain distance from an overlying surface mesothelium.
Twenty cases of adenomatoid tumors and four cases of reactive submesothelia
l lesions, characterized by marked proliferation of subserosal mesenchymal
cells, were reviewed. Nineteen of twenty adenomatoid tumors, including lesi
ons with ill-defined borders, showed no connection with surface mesothelium
. At the periphery of small tumors, isolated glands, clusters of epithelioi
d cells and single epithelioid, and spindled cells showing no connection to
adjacent glands or cell clusters were identified. The tumor cells shared f
eatures with reactive subserosal stromal cells including an infiltrative pa
ttern and histochemical and immunohistochemical properties.
The differences between adenomatoid tumors and reactive submesothelial tiss
ue are quantitative in nature: predominant amount of spindled cells in reac
tive submesothelial lesions, and predominant amount of glandlike structures
in adenomatoid tumors. It is proposed that adenomatoid tumors arise from p
luripotent mesenchymal cells that differentiate toward submesothelial cells
and eventually mesothelial cells. This differentiation is probably induced
by the adjacent submesothelial cells.