A 28-year-old woman presents with severe dysmenorrhea and dyspareunia for 2 years. Pelvic examination reveals a tender, fixed adnexal mass. Coronal MRI pelvis is performed. The structure marked **B** shows a cystic lesion that is T1 hyperintense with T2 hypointense "shading." What is the most likely diagnosis?

Explanation

## Why Chocolate cyst (endometrioma) is right The classic MRI appearance of an endometrioma (chocolate cyst) is T1 hyperintensity due to blood products and hemosiderin, combined with T2 hypointensity and the pathognomonic "shading sign." This represents ectopic endometrial tissue within the ovary, which occurs in ~10% of reproductive-age women. The clinical triad of dysmenorrhea, dyspareunia, and the imaging findings are diagnostic of ovarian endometriosis. (Williams Gynecology 4e) ## Why each distractor is wrong - **Simple ovarian cyst**: Simple cysts are T2 hyperintense (fluid signal) with no T1 hyperintensity or shading; they do not cause dyspareunia or dysmenorrhea. - **Ovarian fibroma**: Fibromas are solid, T2 hypointense lesions without T1 hyperintensity; they do not contain blood products and are not associated with endometriosis symptoms. - **Dermoid cyst (mature teratoma)**: Dermoids show fat-fluid levels and variable T1/T2 signal depending on lipid content, but lack the characteristic T1 hyperintensity with T2 shading sign; they are not associated with dysmenorrhea or dyspareunia. **High-Yield:** Chocolate cyst = T1 hyperintense + T2 hypointense shading sign + dysmenorrhea/dyspareunia = endometrioma on ovary. [cite: Williams Gynecology 4e]