 The best known of these surgeries are those that reshape the genitals, which are also known as "genital reassignment surgery" or "genital reconstruction surgery" (GRS)- or "bottom surgery" (the latter is named in contrast to "top surgery", which is surgery to the breasts; bottom surgery does not refer to surgery on the buttocks in this context).However, the meaning of "sex reassignment surgery" has been clarified by the medical subspecialty organization, the World Professional Association for Transgender Health (WPATH), to include any of a larger number of surgical procedures performed as part of a medical treatment for "gender dysphoria" or "transsexualism".According to WPATH, medically necessary sex reassignment surgeries include "complete hysterectomy, bilateral mastectomy, chest reconstruction or augmentation ... including breast prostheses if necessary, genital reconstruction (by various techniques which must be appropriate to each patient ...)... and certain facial plastic reconstruction."