Synopsis
Explain how follicular and corpus-luteum cysts arise, distinguish a physiological transient cyst from important mimics, and choose safe observation, reassessment or escalation without unnecessary surgery.
- A follicular cyst forms when a dominant follicle does not rupture or regress; a corpus-luteum cyst forms after ovulation and may contain blood, giving it a thicker or more complex appearance.
- Many premenopausal simple cysts are physiological. RCOG states that a thin-walled simple cyst under 50 mm usually resolves within two to three menstrual cycles and generally needs no routine follow-up.
- For an asymptomatic simple cyst measuring 50–70 mm, yearly ultrasound follow-up is advised; a cyst larger than 70 mm merits further imaging such as MRI or consideration of surgery because ultrasound may not show the whole lesion reliably.
- Transvaginal ultrasound characterises wall, locules, internal echoes, solid components, papillary projections, vascularity and free fluid; transabdominal imaging complements it when the lesion extends beyond the pelvic field.
- Do not order CA125 routinely for a clearly simple cyst in a premenopausal patient: menstruation, endometriosis, fibroids and infection can raise it, while a normal value does not exclude early cancer.
- Combined oral contraception does not make an existing functional cyst resolve sooner, although contraceptive choice may independently reduce future ovulation and should be discussed for its usual indications.
- Persistence, growth, new symptoms or changing morphology argues against a transient functional cyst and should prompt repeat characterisation and gynaecology assessment.
- Observation requires a named result owner and explicit advice to seek urgent care for sudden severe pain, vomiting, faintness or worsening abdominal distension.