Cortical inclusion cyst

What is a cortical inclusion cyst?

A cortical inclusion cyst is a non-cancerous change that is commonly seen when the ovary from a reproductive-age woman is examined under the microscope. It is a small hole that forms from a break in the epithelium on the surface of the ovary. Pathologists use the word cyst to describe any abnormal open space in a tissue sample. The break develops when the ovum is released during ovulation. If the break does not repair fully, a cortical inclusion cyst is left behind. There can be a single cyst or multiple cysts within the ovary.

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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