Phenotypic Characterisation of the Inner and Outer Myometrium in Normal and Adenomyotic Uteri

Abstract

Background and Aim: To study the characteristics of the inner (IM) and outer (OM) myometrium in the presence and absence of uterine adenomyosis. Methods: Case control blinded comparison carried out in a university department. Morphometric features of the myometrium were studied in uteri from pre- and postmenopausal women with and without uterine adenomyosis as the sole pathology. Uteri were also divided according to the phase of the cycle and examined using immunohistochemistry and image analysis. Results: Cell density and total nuclear area were statistically significantly greater in the IM compared to OM, in pre- and postmenopausal women, in both the adenomyosis and control uteri. The difference in nuclear size was statistically significant only in the premenopausal group. The change from the IM to the OM in cell density and total nuclear area was gradual with no distinct zonation. Examined features did not vary with cycle phase. Both the IM and OM in adenomyosis exhibited lower cell density and larger nuclei compared to controls. In adenomyosis, immunostaining for α-smooth muscle actin, desmin and Ki-67 was consistent with myometrial hyperplasia and hypertrophy. Conclusions: There are clear differences between the IM and the OM but the transition is gradual, with no distinct zonation. Adenomyosis is characterised by reduced cell density, and increased nuclear size and features of hyperplasia and hypertrophy that are not confined to the IM.