Mass lesions of the myometrium: interpretation and management of unexpected pathology

Uterine leiomyomas are the most common benign uterine smooth muscle tumors. On the basis of imaging, these masses are often presumed to be benign conventional leiomyomas and surgical excision is a common treatment choice. After myomectomy or hysterectomy for presumed leiomyomas, the surgical pathology report may reveal an unexpected diagnosis of another type of mesenchymal tumor. These can range from a variant of benign smooth muscle tumors to smooth muscle tumors of uncertain malignant potential to malignant sarcomas. This review describes these variant pathologies and reviews data on recurrence risk and postoperative management.

The majority of benign smooth muscle tumors will be classified as leiomyomas. Cellular, bizarre nuclei, mitotically active, epitheliod, myxoid, and dissecting are all terms that describe pathologic variants of benign leiomyomas. Smooth muscle tumors of uncertain malignant potential contain both benign and malignant features and should be referred to Gynecologic Oncology for follow-up. Leiomyosarcomas and low-grade endometrial stromal sarcomas may present preoperatively as benign tumors but are malignant with a high risk of recurrence and should be referred to Gynecologic Oncology.

We advocate for the continued benefits of minimally invasive procedures in appropriately selected patients. Despite these measures, unexpected pathologic diagnoses can occur and should be managed appropriately.