74 A Rare Case of Heterotopic Ossification in an Extrauterine Leiomyoma

Introduction/Objective Heterotopic ossification is a histologic finding where mature lamellar bone inappropriately forms in soft tissue, often as a result of trauma or tissue injury. While this finding is occasionally seen in uterine tissue, it is rarely encountered in extrauterine fibroids. Methods/Case Report Here we present a case of a nulliparous 40 year-old female with a 10-year history of progressive abnormal uterine bleeding and pelvic pain. Ultrasound revealed multiple fibroids that grew over 10-years, the largest measuring up to 10.9 cm on MRI. These lesions were ultimately resected via total abdominal hysterectomy. During the procedure, a smaller 3-4 x 2 cm extrauterine fibroid was found to have parasitized to the rectum and mesentery. Sections were submitted for histologic evaluation following decalcification, revealing this tissue to be a benign calcified leiomyoma with focal heterotopic ossification with bone marrow elements present, a rare finding in premenopausal individuals believed to result from long standing inadequate blood supply to the leiomyoma. The differential diagnosis may include sarcoma or carcinosarcoma with heterotopic sarcomatous elements. Results NA Conclusion This case highlights a rare reactive change, not to be confused with sarcoma, that pathologists may encounter when examining long standing leiomyomas, including those found outside the uterus.