Cotyledonoid Dissecting Leiomyoma: A Rare Case With Rapid Regrowth After Fertility-Sparing Surgery and Hormonal Therapy.

Cotyledonoid dissecting leiomyoma (CDL) is a rare benign variant of uterine leiomyoma. Its multinodular, placental-like morphology often mimics malignant tumors, leading to overtreatment.  We report a case of a 34-year-old nulliparous Japanese woman who presented with abdominal distension and urinary frequency, and was subsequently diagnosed with CDL. MRI revealed a 30 cm heterogeneous uterine mass. She desired to preserve fertility, so myomectomy was planned. However, because of the tumor's characteristics, complete resection was difficult and partial resection of the tumor was performed due to intraoperative bladder injury, leaving an 8 cm residual tumor. Histopathology confirmed CDL. Despite postoperative gonadotropin-releasing hormone (GnRH) antagonist therapy, the tumor enlarged to 13 cm over nine months. 18F-fluoroestradiol (18F-FES) PET showed no tracer uptake. At the time of presentation to our hospital, she no longer desired fertility preservation. Therefore, she underwent a total hysterectomy with right salpingectomy as the second surgery, and histology confirmed recurrent CDL. She remains disease-free two years postoperatively. CDL is a histologically benign tumor that can exhibit aggressive behavior when incompletely excised. Hormonal therapy appears to have limited efficacy, possibly due to impaired or functionally inactive hormone receptors. Complete surgical resection remains essential to prevent recurrence, whereas fertility-sparing surgery should be considered only when complete removal is technically achievable. Greater awareness of this rare but deceptive entity may help clinicians avoid unnecessary radical procedures and optimize outcomes for affected women.