Membranous dysmenorrhea and decidual casts: A scoping review

BACKGROUND: Membranous dysmenorrhea, characterized by the expulsion of intact endometrial tissue rather than gradual dissolution during menstruation, occasionally presents as a decidual cast-a complete triangular mold of the uterine cavity. This poorly understood condition is likely underdiagnosed. OBJECTIVES: This study maps and describes the existing English literature on membranous dysmenorrhea and decidual cast expulsion, focusing on clinical presentation, etiology, and management. SEARCH STRATEGY: A scoping review was conducted according to Joanna Briggs Institute methodology and PRISMA-ScR guidelines. PubMed, EMBASE, Web of Science, and CINAHL were searched using the terms "membranous dysmenorrhea," or "membranacea dysmenorrhea," or "decidual cast," limited to English-language publications. The final search was performed in February 2026. Google Scholar and manual screening of references supplemented the search. SELECTION CRITERIA: English-language full text publications reporting on membranous dysmenorrhea or decidual cast expulsion were included, encompassing case reports, case series, and observational studies. DATA COLLECTION AND ANALYSIS: Data extracted included publication type, geographical origin, patient demographics, clinical features, and management approaches. Thematic analysis was performed to identify key patterns. MAIN RESULTS: One hundred and thirteen publications met inclusion criteria, including 86 case reports/series describing 121 individual cases, plus 42 additional cases from a single-author report. Patient ages ranged from 9 to 53 years. Most cases involved vaginal passage of tissue, with or without pain. Early reports noted spontaneous and recurrent episodes, while recent cases were often sporadic and involved hormonal treatments, particularly progestins. Additional associations were infection, ectopic pregnancy, pregnancy in uterus bicornis/didelphys, and postpartum hemorrhage. Proposed etiologies include hormonal influences (endogenous/exogenous progesterone), endometritis, or normal menstruation variants. Most cases resolved without intervention. Some required dilatation and evacuation of the uterine cavity. CONCLUSION: Membranous dysmenorrhea and decidual cast expulsion are benign phenomena that might cause diagnostic confusion and unnecessary interventions. Increased clinical awareness is essential for appropriate counseling and to distinguish this condition from early pregnancy loss. Hormonal contraceptives might act as both triggers and therapeutic agents. Further research beyond case reports is needed.