Mucinous cystadenoma of the ovary

by Emily Goebel, MD FRCPC
June 7, 2023

What is mucinous cystadenoma?

A mucinous cystadenoma is a non-cancerous type of ovarian tumour.  While these tumours are non-cancerous, they can grow to be very large in size and can cause significant symptoms for many patients.

How do pathologists make this diagnosis?

For most women, the diagnosis of mucinous cystadenoma is only made when the entire tumour has been surgically removed and sent to a pathologist for examination. The fallopian tube and uterus may be removed at the same time.

Your surgeon may request an intraoperative or frozen section consultation from your pathologist. The diagnosis made by your pathologist during the intraoperative consultation can change the type of surgery performed or the treatment offered after the surgery is completed.​

Most tumours are similar in look and feel to a balloon filled with fluid. The inside of the tumour may be one large space or many small spaces filled with fluid. Pathologists call these spaces cysts.

When the tumour is examined under the microscope, the tissue on the inside of the cysts is made up of an abnormal type of epithelium that produces a thick, gelatinous fluid called mucin. The mucin fills the inside of the tumour.

Some tumours will have thicker walls or solid areas in the centre of the tumour. These tumours contain more cells and less fluid and are called mucinous cystadenofibromas. However, they are still non-cancerous.

Atypia

Atypia is a word pathologists use to describe cells that look different from cells normally found in that location. Most mucinous cystadenomas do not contain any atypical cells. A tumour with atypical cells is sometimes called a mucinous tumour with focal atypia.

Examination of the tumour surface

Most mucinous cystadenomas have a smooth outer surface. Any solid areas on the surface will be examined closely under the microscope to make sure they do not contain any abnormal cells.

Epithelial proliferation

The inner surface of most mucinous cystadenomas are lined by a flat single layer of cells. Some tumours, however, have small growths or proliferations of the mucinous epithelium that make them look more complex when examined under the microscope.  If the tumour has areas with these features, it may be called a mucinous tumour with focal epithelial proliferation.