MRI-based Classifications for adenomyosis
According to the typical classification (classification 1), adenomyosis was mainly classified as focal adenomyosis and diffuse adenomyosis. Adenomyosis is defined as focal when the lesion is surrounded by circumscribed adenomyomas in the inner one third of the myometriun, whereas diffuse adenomyosis is diagnosed when the lesion extends to the outer two thirds of the myometrium and up to gross involvement of the entire uterus14. According to Kishi et al5 (classification 2), adenomyosis was divided into four groups based on different etiologies: subtype I (intrinsic), subtype II (extrinsic), subtype III (intramural), and subtype IV4 (indeterminate). Subtype I is characterized by the invagination of the basal endometrium into the myometrium without affecting the outer myometrial layer, while subtype II directly invades uterine serosa from peritoneal or pelvic endometriosis without affecting the inner myometrial layer5. According to Bazot and Daraï7(classification 3), we defined adenomyosis as three subtypes: internal (similar to intrinsic), external (similar to extrinsic), and adenomyomas (similar to intramural adenomyoma). According to Kobayashi et al8 (classification 4), we categorized patients into six subtypes on the basis of affected areas and volumes, i.e., subtype 1-3 (internal adenomyosis) and subtype 4-6 (external adenomyosis). Subtype 1 and subtype 4 represent the volumes <1/3 of uterine wall; subtype 2 and subtype 5 represent the volumes <2/3 of uterine wall; subtype 3 and subtype 6 represent the volumes ≥2/3 of uterine wall. According to Gong et al9 (classification 5), adenomyosis could be classified as internal adenomyosis (asymmetric internal as subtype 1, symmetric internal as subtype 2), external adenomyosis (asymmetric external as subtype 3), intramural adenomyosis (subtype 4), and full thickness adenomyosis (asymmetric full thickness as subtype 5, symmetric full thickness as subtype 6).