A 28-year-old woman presents with 8 weeks amenorrhea and vaginal bleeding. Transvaginal ultrasound shows a 1.8 cm unilocular anechoic cyst in the right adnexa and a live intrauterine pregnancy. Serum β-hCG is 12,000 mIU/mL. What is the most likely explanation for the adnexal finding?
- A Coexisting ectopic pregnancy (heterotopic pregnancy)
- B Dermoid cyst (mature cystic teratoma)
- C Corpus luteum cyst of pregnancy ✓
- D Hydrosalpinx
Correct answer: C. Corpus luteum cyst of pregnancy
Explanation
A simple unilocular anechoic adnexal cyst in early pregnancy is most commonly a corpus luteum cyst, which produces progesterone to support the pregnancy until the placenta takes over. Heterotopic pregnancy (coexisting intrauterine and ectopic) is rare (approximately 1 in 30,000 in spontaneous conceptions) and would show a more complex adnexal mass, not a simple cyst. Dermoid cysts have characteristic echogenic components. Hydrosalpinx appears as a tubular, fluid-filled structure, not a simple unilocular cyst.
Reference: Callen's Ultrasonography in Obstetrics and Gynecology, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.