In this radiology lecture, we review the ultrasound appearance of endometrioma through three unique cases, including an MRI example. Key teaching points include: * Endometriosis = Ectopic endometrial glands and stroma outside of the uterine cavity. Includes endometriomas, extraovarian implants and adhesions. * Endometriomas = Endometriotic cysts within ovary. * Endometriosis is seen in about 10% of women of reproductive age. * Presentation: Pelvic pain, dysmenorrhea, dyspareunia, infertility. * Ultrasound: Diffuse, homogeneous low-level echoes (most specific feature) yielding a ground glass appearance. May have posterior acoustic enhancement. * Endometriomas may have peripheral punctate echogenic foci. These foci have no internal vascular flow but can see twinkle artifact. * Vascular flow may be present in endometrioma septations. * Endometrioma vs. hemorrhagic cyst: Hemorrhagic cysts are acute, usually solitary and unilocular, whereas endometriomas are chronic, sometimes multiple and multilocular. * Endometriomas can rarely (1%) undergo malignant transformation into endometrioid carcinoma or clear cell carcinoma. * MR is the most specific imaging modality for diagnosis of endometrioma = Specificity 98%.* * Homogeneous, T1 “light bulb” bright, T2 dark = “T2 shading.” * Surgical treatment: Depends on disease severity from laparoscopic cyst aspiration/cystectomy to hysterectomy/oophorectomy. * Medical management may be attempted: Oral contraceptives, GnRH agonists *Reference: Togashi K, Nishimura K, Kimura I, et al. Endometrial cysts: Diagnosis with MR imaging. Radiology. 1991;180:73-78. To learn more about the Samsung RS85 Prestige ultrasound system, please visit: https://www.bostonimaging.com/rs85-prestige-ultrasound-system-4 Click the YouTube Community tab or follow on social media for bonus teaching material posted throughout the week! Instagram: https://www.instagram.com/radiologistHQ/ Facebook: https://www.facebook.com/radiologistHeadQuarters/ Twitter: https://twitter.com/radiologistHQ