Abstract
RATIONALE: Cotyledonoid dissecting leiomyoma (CDL) is an exceptionally rare and morphologically unusual benign uterine leiomyoma. Its malignant-mimicking radiographic and intraoperative features pose a significant diagnostic challenge, often leading to misinterpretation and potentially overtreatment. This case is reported for its rarity and to highlight the critical importance of pathological recognition. PATIENT CONCERNS: A 23-year-old female presented with a recurrent pelvic mass detected during a routine follow-up examination 2 years after the initial surgical resection of a uterine mass. The patient was asymptomatic. DIAGNOSES: Histopathological examination of both the initial and recurrent masses confirmed the diagnosis of CDL. The specimens exhibited characteristic features including intramural dissecting growth and an exophytic, cotyledon-like nodular appearance. INTERVENTIONS: The patient underwent surgical excision for both the primary uterine mass and the recurrent pelvic mass. OUTCOMES: The patient recovered well postoperatively with no complications. No evidence of disease was found at the most recent follow-up visit. LESSONS: This case represents the first documented instance of recurrent CDL in China and only the second reported globally. It underscores that recurrence, although exceedingly rare, is a possible outcome for CDL. Pathological confirmation is paramount to achieve an accurate diagnosis, avoid a misdiagnosis of malignancy, and prevent unnecessary radical surgery or adjuvant therapy, thus preserving fertility and quality of life in young patients.