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Selected images from a first trimester ultrasound.
There is a hypoechoic, centrally cystic cyst in the left ovary. On color Doppler imaging, there is a characteristic "ring of fire" appearance to the cyst. In the setting of an intra-uterine pregnancy (gestational sac with a yolk sac +/- embryo), this is cystic lesion is characteristic of a corpus luteum. In the absence of an intrauterine pregnancy, it may still be a corpus luteum cyst, but one should maintain suspicion for a possible ectopic pregnancy.