Cumulus oophorus

Last revised by Dennis Odhiambo Agolah on 6 Aug 2022

Cumulus oophorus refers to an appearance in the ovary in which multiple granulosa cells enlarge around a developing oocyte. These support cells ("cumulus cells") serve multiple functions in the maturation of the oocyte. They may occasionally be seen during a pelvic ultrasound, and should not be confused with a pathological finding.

60-65% of the time a cumulus oophorus is visualized 12-24 hours before ovulation 3.

It comprises a collection of the cells in a mature follicle that protrude into the cavity of the follicle. It is a sign of imminent ovulation, but its absence has little significance in predicting the maturity of the oocyte. 

On ultrasound, the cumulus oophorus appears as a cyst along the wall of the dominant follicle

Radiographic features

  • it may be seen as a small anechoic cyst (or group of cysts) around a dominant follicle

Differential diagnosis

  • septated ovarian cyst: the stage of the menstrual cycle may help differentiate​

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