KEY FACTS
Terminology
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Follicular cyst (FC) forms from persistent follicle, ovulation does not occur
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Corpus luteum cyst (CLC) forms from graafian follicle following ovulation
Imaging
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FC: Intraovarian cystic lesion with thin walls
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CLC: Occur after ovulation in latter part of menstrual cycle
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Thick, hyperechoic wall
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Central anechoic/hypoechoic cavity
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Marked vascular flow within CLC wall: “Ring of fire”
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Commonly complicated by hemorrhage
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Top Differential Diagnoses
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Ectopic pregnancy: “Ring of fire” separate from ovary, usually tubal ectopic
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Ovarian neoplasm
Clinical Issues
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FC and CLC occur during reproductive years
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FL and CLC ≤ 5 cm: No follow-up necessary
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FL and CLC > 5 and ≤ 7 cm: Annual follow-up ultrasound
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Further imaging or surgical evaluation recommended with simple cyst > 7 cm
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Follow-up imaging in 6-12 weeks recommended with hemorrhagic cyst > 5 cm
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CLC may enlarge initially with fertilization and pregnancy
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Most no longer seen by sonography by early 2nd trimester (16 weeks)
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Malignancy rate in unilocular simple cysts: < 1%
Diagnostic Checklist
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Majority of functional ovarian cysts will resolve spontaneously
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Even if CLC is persistent, may monitor through pregnancy if no malignant features
Scanning Tips
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Gentle transducer pressure, manual external compression, or scanning while patient coughs may help confirm intraovarian location of CLC vs. tubal ectopic pregnancy, which would be located separate from ovary
arising from the left ovary.
; If in doubt, look for the bridging ovarian parenchyma 
in continuity with CLC. Gentle pressure on the ovary with the transducer can also help demonstrate that the CLC arises from the ovary. Small retracted clot is present within this CLC 
.
