An immunohistochemical and ultrastructural investigation on the presence of "smooth muscle differentiation" in stromal ovarian tissue was carried out in 10 adult
granulosa cell tumors, six juvenile
granulosa cell tumors, six
thecoma/fibrothecomas, six cases of stromal
hyperplasia, and in 10 normal ovaries. For immunohistochemistry,
formalin-fixed
paraffin-embedded tissues were processed using anti-alpha smooth muscle actin (alpha-SM actin) and anti-
desmin as primary
monoclonal antibodies. All adult
granulosa cell tumors and juvenile
granulosa cell tumors showed an intense alpha-SM actin immunoreaction, but weaker for
desmin. Immunostain was diffuse in six out of 10 and five out of six adult
granulosa cell tumors and juvenile
granulosa cell tumors, respectively. Ultrastructurally, intermediate filaments focally converging into well developed desmosomes as well as peripheral bundles of myofilaments were documented both in adult
granulosa cell tumors and juvenile
granulosa cell tumors. In
thecoma/fibrothecomas and stromal
hyperplasia, alpha-SM actin and
desmin expression was minimal or absent; on electron microscopy some "myoid" features and myofibroblasts were also seen. In normal ovaries, alpha-SM actin was found intensely expressed in the theca externa, focally identified in cortex-medulla, and unstained in the theca interna layer. Immunoreaction increased during folliculogenesis, going from a thin positive alpha-SM actin layer around secondary follicles to a strong diffuse
stain in mature follicles. Our immunohistochemical and ultrastructural results indicate that a "smooth muscle differentiation" is a typical component of the specialized gonadal stromal tissue. A diffuse and focally alpha-SM actin is constantly present in
granulosa cell tumors and
thecoma/fibrothecomas, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)