Corpus luteum

Vaginal

ultrasound showing a 25 millimeter wide corpus luteum with a fluid-filled cavity in its middle (shown as dark in the image since it is anechoic). The rest of the ovary is seen at right, with 3 small follicles seen in the same plane. The woman was pregnant at 9 weeks of gestational age.

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The corpus luteum (plural: corpora lutea) is a temporary endocrine structure involved in ovulation and early pregnancy.

During ovulation, the primary follicle forms the secondary follicle and subsequently the mature vesicular follicle.

At ovulation the follicle ruptures expelling the ovum into the fallopian tube. The remnants of the follicle after ovulation is referred to as the corpus luteum and ranges from 2-5 cm in diameter but involutes as it matures. The corpus luteum produces estrogen and progesterone, maintaining optimum conditions for implantation if the ovum is fertilised:

fertilised: the corpus luteum continues to produce these hormones and maximizes the chance of implantation into the endometrium; it reaches a maximum size at ~10 weeks and finally resolves at around 16-20 weeks
not fertilised: the corpus luteum involutes and turns into a corpus albicans by around 2 weeks

In some instances (especially in twin pregnancies), there may be more than one corpus luteum - (e.g. two corpora lutea)

Radiographic features

Ultrasound

The corpus luteum is a thick walled cyst with characteristic "ring of fire" peripheral vascularity. It usually has a crenulated inner margin and internal echoes.

Differential diagnosis

General considerations include:

adnexal ectopic pregnancy
- ectopic pregnancy is more echogenic than the ovary in 77-88%
- corpus luteum is more echogenic than the ovary in ~3%
ovarian neoplasm

History and etymology

The term "corpus luteum" is derived from the Latin meaning "yellow body" where "corpus" means body and "luteum" means yellow. The corpus luteum eventually involutes into the "corpus albicans" ("white body").