Diffuse Adenomyosis Coexisting with rASRM Stage IV Endometriosis in a Young Woman: Diagnostic Delay and Imaging Discrepancy.

Introduction: Adenomyosis is increasingly recognized in young women and frequently coexists with endometriosis, suggesting shared pathogenic mechanisms. Delayed recognition of symptoms may contribute to disease progression, while discrepancies between preoperative imaging and intraoperative findings remain a diagnostic challenge. We report a case of diffuse adenomyosis coexisting with revised American Society for Reproductive Medicine (rASRM) stage IV endometriosis, highlighting diagnostic delay and the complementary roles of transvaginal ultrasound (TVUS), magnetic resonance imaging (MRI), and laparoscopy. Case Presentation: A 22-year-old nulligravid woman presented with severe dysmenorrhea since adolescence, accompanied by dyschezia, dysuria during menstruation, and chronic pelvic pain. TVUS demonstrated diffuse posterior adenomyosis according to the Morphological Uterus Sonographic Assessment (MUSA) criteria, bilateral ovarian endometriomas, left hydrosalpinx, a posterior compartment lesion suspicious for deep infiltrating endometriosis (DIE), and a negative sliding sign suggestive of pelvic adhesions. TVUS identified posterior compartment DIE and pelvic adhesions that were subsequently confirmed during laparoscopy, whereas MRI confirmed diffuse adenomyosis and bilateral adnexal disease without identifying posterior compartment involvement. Fertility-preserving laparoscopic adhesiolysis, adenomyomectomy, bilateral ovarian cystectomy, and left salpingectomy were performed. Histopathological examination confirmed adenomyosis and bilateral ovarian endometriomas. Postoperatively, the patient was commenced on dienogest while awaiting future fertility treatment. Discussion: This case demonstrates that adenomyosis may occur in young women and coexist with advanced endometriosis. The close anatomical relationship between posterior adenomyosis and posterior DIE provides clinical support for the outside-to-inside pathogenic hypothesis. In this case, TVUS outperformed MRI in detecting posterior compartment disease, illustrating the complementary strengths of multimodal imaging, with laparoscopy remaining the reference standard for definitive assessment. Conclusion: Persistent dysmenorrhea in young women should not be considered a normal menstrual symptom. Early specialist referral and comprehensive multimodal imaging assessment are essential to reduce diagnostic delay, facilitate fertility-preserving management, and improve recognition of advanced adenomyosis and endometriosis.