Follicle cysts and cystic follicles of the ovary

What are follicle cysts and cystic follicles?

Follicle cysts and cystic follicles are non-cancerous changes commonly seen when the ovary from a reproductive-age woman is examined under the microscope. They are created by the growth of a developing follicle that did not release its ovum during the menstrual cycle. As the follicle grows, an open space called a cyst develops in the center of the follicle.

A cyst that measures less than 3 cm is called a cystic follicle. A cyst that measures more than 3 cm in size is called a follicle cyst. These generally do not cause symptoms. However, a large follicle cyst can rupture and cause pelvic pain.

The ovary

The ovaries are part of the female reproductive tract. They are small organs that are attached to the uterus by the fallopian tubes. The outer surface of the ovary is lined by a thin layer of specialized tissue that forms a barrier around the outside of the ovary called the epithelium.

The tissue below the epithelium is called the stroma. Within the stroma are large cells called ova which contain half of the genetic material necessary to create a new human being. The other half of the genetic material comes from the male sperm cell during fertilization.

Gynecological tract

Ova are surrounded by specialized stromal cells that support the ovum until it is released from the ovary. The ovum and stromal cells form small round structures called follicles. These follicles send and receive signals that create the menstrual cycle.

Normal ovary

Every month, a small number of follicles begin to mature until one ovum (but sometimes more) is released from the ovary. This is called ovulation. The released ovum breaks through the epithelium on the surface of the ovary before entering the fallopian tube.

The follicle that is left behind in the ovary is called the corpus luteum. If fertilization does not occur, the corpus luteum becomes the corpus albicans. Both the corpus luteum and corpus albicans can be seen when an ovary is examined under the microscope by a pathologist.

by Emily Goebel MD FRCPC, updated December 15, 2020
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