Functional Ovarian Cysts
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Direct answer
Functional ovarian cysts are physiological follicular or luteal cysts that form during the menstrual cycle and usually resolve within a few cycles. The three main types are follicular cysts, corpus luteum cysts and theca lutein cysts, and most need only observation. Surgery is reserved for torsion, haemorrhage or a cyst that persists or looks suspicious on ultrasound.
What you must remember
- Follicular cyst: A persistent unruptured follicle, typically unilocular with a thin wall and no internal solid component.
- Corpus luteum cyst: Forms after ovulation and can bleed, causing haemoperitoneum if it ruptures.
- Ring of fire: Peripheral vascularity around a corpus luteum on colour Doppler, a useful distinguishing sign.
- Theca lutein cyst: Bilateral, multiloculated and enlarged ovaries linked to high hCG states such as molar pregnancy, choriocarcinoma and multiple pregnancy.
- Conservative approach: Most simple cysts in premenopausal women resolve, so repeat ultrasound after about 6 to 8 weeks is the usual approach.
- Oral contraceptives: Combined pills suppress ovulation and may help a persistent follicular cyst.
- Surgical indications: Torsion, rupture with haemodynamic compromise, a cyst persisting beyond about 8 to 12 weeks, or features suspicious for neoplasm.
Three cysts, three causes, one approach
A young woman has a 4 cm unilocular cyst on ultrasound and mild pelvic pain. The table sets out how the three functional cysts differ in origin, appearance and management. Most are found incidentally on scan, so the cyst size should be recorded at each review.
| Cyst | Origin | Key feature | Usual management |
|---|---|---|---|
| Follicular | Unruptured follicle | Thin-walled, unilocular | Observe; pill if persistent |
| Corpus luteum | Luteinised follicle after ovulation | Ring of fire, may bleed | Observe; preserve in early pregnancy |
| Theca lutein | Stimulation by high hCG | Bilateral, multiloculated | Treat the cause; expect regression |
The cause and the hCG status matter more than size alone. Surgery is needed only when a complication or a suspicious feature appears.
Follow-up scans are best compared at the same point in the cycle, since follicles and luteal cysts change with it. A cyst that has disappeared on repeat scan needs no further action. Persistent cysts beyond the usual interval are reassessed before any surgery is planned.
Where the exam tries to catch you
Most traps involve removing a cyst that would have resolved, or missing a cyst that needs urgent care.
- Trap: Operating on every functional cyst above 3 cm Correct: Simple cysts in premenopausal women are usually followed up, since most resolve without surgery.
- Trap: Removing a corpus luteum in early pregnancy Correct: It supports the pregnancy, so it is preserved unless torsion or rupture forces surgery.
- Trap: Treating bilateral multiloculated ovaries as a neoplasm without checking hCG Correct: Theca lutein cysts with raised hCG are expected, so the hCG is checked and the cause treated first.
Frequently asked questions
Which functional ovarian cyst is associated with high hCG levels?
Theca lutein cysts are the functional cysts linked to high hCG levels. They are typically bilateral and multiloculated, and they occur in molar pregnancy, choriocarcinoma, multiple pregnancy and ovulation induction. Their size usually falls as the hCG level falls.
When is surgery indicated for a functional ovarian cyst?
Surgery is indicated for torsion, rupture with haemodynamic instability, or a functional cyst that persists beyond about 8 to 12 weeks. Ultrasound features suspicious for neoplasm also prompt surgery. Simple cysts that resolve on follow-up do not need an operation.
Why should a corpus luteum cyst be preserved in early pregnancy?
A corpus luteum cyst produces progesterone that sustains the early pregnancy until the placenta takes over. Removing it before that transition can cause pregnancy loss. Surgery is therefore avoided unless torsion or rupture forces the decision.
What is the ring of fire sign on colour Doppler?
The ring of fire sign is peripheral vascularity around the wall of a corpus luteum cyst on colour Doppler. It helps distinguish a corpus luteum from a neoplasm, which typically shows internal vascularity within solid components. The sign is most useful when the appearance is otherwise uncertain.
How long should a simple functional cyst be observed before surgery?
A simple functional cyst is usually reviewed with repeat ultrasound after about 6 to 8 weeks, because most resolve in that time. Persistence beyond that interval, or a change in features, prompts further evaluation. Oral contraceptives may be used for a persistent follicular cyst.