A 26-year-old woman is being evaluated for lower abdominal discomfort. Medical history is significant for mild intermittent asthma and migraines without aura. She has never been pregnant. The patient is sexually active with her husband and they use condoms for contraception. She drinks alcohol socially and does not use tobacco or illicit drugs. Her mother was diagnosed with breast cancer at age 52 and her grandfather died of colon cancer at age 77. BMI is 30 kg/m². Ultrasound of the abdomen reveals a right-sided adnexal mass that is subsequently removed with laparoscopic surgery. Histologic findings are shown in the image below: Which of the following is the most likely diagnosis?

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11ec160b_3923_5230_9249_377b805df009_MD0001_00 This patient has a mature teratoma, the most common subtype of ovarian germ cell neoplasm. They are primarily found in women age 10-30. Most patients are asymptomatic and found to have an incidental mass on pelvic examination or ultrasound, but some can present with pain or abdominal discomfort. Teratomas are characterized by the presence of tissue from multiple germ layers (ectoderm, mesoderm, and endoderm). Morphologically, they are subclassified as benign mature teratomas (contain mature tissue) and malignant immature teratomas (contain mature and immature tissue, commonly fetal neuroepithelium). Mature teratomas are cystic lesions and may contain sebaceous content, hair, and teeth. By microscopy, diverse tissues can be seen, including skin (eg, hair follicles, sebaceous glands), bone, respiratory epithelium, and thyroid tissue. Although mature teratomas are benign, they may seldom develop malignant change (eg, squamous cell carcinoma). (Choice A) In ectopic pregnancy, the blastocyst implants outside the endometrial cavity (eg, fallopian tube). It can be diagnosed with transvaginal ultrasonography and β-hCG measurements. Although ectopic pregnancy may present with abdominal pain, histologic evaluation of the mass would reveal chorionic villi. (Choice B) Endometriosis is characterized by endometrial tissue implanted outside the uterine cavity. Ovarian endometriosis may present with abdominal pain and an adnexal mass; however, microscopic examination would show endometrial glands and stroma. (Choice C) High-grade serous ovarian carcinoma usually presents in older women. Typical histologic features include ovarian stromal invasion by atypical cells (pleomorphic, large, irregular nuclei and prominent nucleoli) forming papillae and glandular spaces. (Choice E) Polycystic ovary syndrome presents with clinical/biochemical evidence of hyperandrogenism and oligo/anovulation. Ultrasound would reveal polycystic ovaries (rather than a unilateral adnexal mass), and microscopy would reveal cystic follicles and stromal fibrosis. Educational objective: Teratomas are the most common subtype of ovarian germ cell neoplasms and occur most frequently in women age 10-30. Mature teratomas are benign and show mature tissues derived from multiple germ layers, frequently including skin, hair, and teeth. __________ References: Germ cell tumors of the gonads: a selective review emphasizing problems in differential diagnosis, newly appreciated, and controversial issues. (http://www.ncbi.nlm.nih.gov/pubmed/15761467)

A 26-Year-Old Woman Is Being Evaluated for Lower Abdominal Discomfort