Sonographic confirmation of an intra-uterine pregnancy. Asymptomatic.
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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 intra-uterine pregnancy, it may still be a corpus luteum cyst, but one should maintain suspicion for a possible ectopic pregnancy.
A corpus luteum is a normal finding in a pelvic ultrasound and should not be misinterpreted as a malignancy.
In the setting of pregnancy (positive beta hCG), the dilemma is whether this finding represents an ectopic pregnancy. In the setting of an intra-uterine pregnancy (IUP), this vascular cyst is overwhelmingly likely to be a corpus luteum rather than an IUP and an ectopic pregnancy (1:30,000).
Without an IUP, one should be much more guarded in diagnosis a vascular adnexal mass as a corpus luteum. If there are concerning clinical features (pain, bleeding) or if there is hemoperitoneum, then an adnexal mass should be considered an ectopic pregnancy until proven otherwise.
Some use the term "corpus luteum" and "corpus luteal cyst" interchangeably. Some reserve the term "corpus luteal cyst" for a corpus luteum in the setting of a first trimester pregnancy.