Corpus Luteum Cyst
This is a corpus luteum cyst, not a follicular cyst, based on the timing 2 weeks before menstruation (luteal phase) and the 6cm size. 1
Physiologic Timing and Cyst Type
The menstrual cycle timing is the critical distinguishing factor here:
- Follicular cysts develop during the follicular/proliferative phase (days 1-14 of the cycle, after menstruation begins) 1
- Corpus luteum cysts occur during the luteal/secretory phase (days 14-28, after ovulation and before the next period) 1
Since this patient is 2 weeks before her period, she is in the mid-to-late luteal phase, making this a corpus luteum cyst by definition 1.
Size Considerations
The 6cm size further supports this diagnosis:
- Physiologic follicles are defined as simple cysts <3cm 1
- Corpus luteum cysts can be larger and still physiologic, though the O-RADS guidelines classify cysts >3cm as requiring follow-up rather than purely physiologic 1
- At 6cm, this exceeds the physiologic corpus luteum definition (<3cm) but remains consistent with a functional luteal cyst that has enlarged 1
Expected Ultrasound Features
If this is a typical corpus luteum cyst, ultrasound may show 1:
- Thick-walled cyst with crenulated (scalloped) inner margin
- Internal echoes (avascular)
- Peripheral vascularity on color Doppler ("ring of fire" sign)
- Smooth wall despite thickness
Management Approach
For this 6cm simple cyst in a premenopausal woman, follow-up ultrasound in 8-12 weeks is recommended to confirm its functional nature and ensure resolution 1. The optimal timing for reevaluation is during the proliferative phase (after her next menstrual period), allowing involution of the functional cyst to occur 1.
Key Management Points:
- No immediate intervention needed for simple cysts 5-10cm in premenopausal women 1
- Repeat imaging in 8-12 weeks to document resolution or reassess for wall abnormalities 1
- If the cyst persists or enlarges on follow-up, gynecologist referral is indicated 1
Common Pitfall to Avoid
Do not prescribe oral contraceptives to "treat" this cyst—combined oral contraceptives do not hasten resolution of functional ovarian cysts and provide no benefit 2. Watchful waiting with repeat imaging is the appropriate strategy 2.