Histogenesis and classification of diffuse and cystic uterine adenomyosis

Purpose: Recently, focal adenomyosis was classified into three subtypes according to magnetic resonance imaging findings: connected to the endometrium (subtype I), connected to the perimetrium (subtype II), and not connected to either the endometrium or the perimetrium (subtype III). However, diffuse adenomyosis and cystic adenomyosis have not been investigated. We attempted to classify diffuse-type adenomyosis and cystic-type adenomyosis according to magnetic resonance imaging findings and verified the validity of the previous classification of focal adenomyosis. Methods: A total of 1504 cases of adenomyosis (focal, n = 1093; nodular, n = 15; diffuse, n = 383; cystic, n = 13) shown in magnetic resonance imaging findings of patients who underwent conservative surgical treatment from 2002 to 2016 at our hospital were reviewed according to the criteria of Kishi. Results: Of the 383 patients with diffuse adenomyosis, 272 (70.8%) were classified as subtype I, while all cases of cystic-type adenomyosis developed in the lateral wall of the uterus were classified as subtype III. Conclusion: Our findings indicate that diffuse adenomyosis develops from the same mechanism as focal adenomyosis subtype I. In addition, we consider that subtype III has greater relationship with cystic adenomyosis than the other types.