Enlarged ovary on ultrasound is usually because of some underlying abnormality. Usually ovaries are about 4 cm in size when measured in greatest dimension with some normal variation. Enlarged ovary on ultrasound is most commonly seen from something within like a cyst or mass. Other causes include infection, torsion or twisting of the ovary, polycystic ovarian syndrome and variations in the menstrual cycle.
The most common reason in my experience to see a significantly enlarged ovary is from a cyst. Most of these are benign cysts or tumors as long as they are simple, meaning entirely composed of fluid and not having any internal nodules, solid components or fluid in the pelvis. Most of the simple cysts can be either ignored or followed if they are large. More complex cysts may need close follow up or evaluation by a surgeon depending on other malignant appearing features. Other masses such as dermoids or benign tumors can increase the size of the ovary as well.
An inflamed ovary can also be enlarged. This is most commonly from pelvic inflammatory disease. It is an ascending infection from the vagina into the uterus, tubes, and ovaries. Usually, there are other findings of inflammation in the pelvis in addition to enlarged ovaries. In late cases, there may be masses where the ovaries are or cavities filled with pus. Dilated Fallopian tubes are also commonly seen.
Ovarian torsion is another cause of enlarged ovary on ultrasound. This is when the ovary and Fallopian tube twists. This can be occasional twisting or persistent. It is a surgical emergency because the ovarian tissue can be permanently injured if not treated. Most commonly, ovarian torsion occurs because of a cyst or mass which leads to twisting. In some cases, the ovary is more mobile than usual. Most patients present with sudden pain, nausea and vomiting. The diagnosis is made with ultrasound. Often the ovary will be enlarged, abnormal in position and have abnormal blood flow. There is often free fluid in the pelvis.
Polycystic ovarian syndrome is a syndrome of excess male hormones called androgens, dysfunction of ovulation and multiple small Follicles in the ovaries. Women with his syndrome will often have enlarged ovaries with multiple follicles or small cysts. The ovaries can also enlarge during ovulation mid cycle as a normal response.
Enlarged ovary on ultrasound can therefore be a benign normal finding all the way to serious conditions like torsion and cancer. Often there is a reason as to why the ovary is enlarged and this is commonly seen on ultrasound. The clinical history will also be important. If your ovary is enlarged and associated with sudden pain onset, than a twisted or torsed ovary becomes the main concern. More chronic pain can be from a cyst or mass.