A cyst is a closed pocket or sac of tissue that typically contains air, fluids, or semi-solid material. While many people ask about cysts forming in the uterus, true fluid-filled sacs within the uterine wall (myometrium) or lining (endometrium) are extremely rare. The masses most frequently found inside the uterus are actually solid tissue growths, not fluid-filled cysts. These fluid-filled structures, correctly called cysts, are most often found on the ovaries, which sit immediately next to the uterus.
Understanding Masses Found in the Uterus
The most common masses detected within the uterus are solid tumors or tissue overgrowths, which are structurally distinct from true cysts. These growths are typically composed of muscle or endometrial tissue, giving them a dense, non-cystic composition. True cysts in the muscular wall of the uterus, known as myometrial cysts, are uncommon lesions. They often arise from cystic degeneration within a fibroid or a condition called cystic adenomyosis.
Masses commonly mistaken for cysts fall into two main categories based on location. The first includes non-cystic growths inside the uterus, such as polyps and fibroids. The second involves true cysts located on adjacent organs, most notably the ovaries, whose close proximity often leads to misidentification.
Endometrial Polyps and Uterine Fibroids
Endometrial polyps are tissue overgrowths that develop from the lining of the uterus (endometrium). These growths are typically attached to the uterine wall by a broad base or a thin stalk and can range in size from a few millimeters to several centimeters. Polyps are generally benign, though they can cause symptoms like irregular menstrual bleeding, spotting between periods, or bleeding after menopause.
The other common uterine mass is the uterine fibroid, also known as a leiomyoma. This is a dense, non-cancerous tumor made of the smooth muscle tissue of the uterine wall. The location of the fibroid significantly determines the symptoms experienced. Submucosal fibroids grow inward into the uterine cavity, often causing the most significant symptoms, such as heavy, prolonged bleeding and subsequent anemia.
Intramural fibroids are situated entirely within the muscular wall of the uterus, leading to pelvic pain or pressure alongside heavy menstrual flow. Subserosal fibroids grow outward on the outer surface of the uterus. Since they do not affect the uterine lining, they rarely cause heavy bleeding. Instead, large subserosal masses often cause “bulk-related” symptoms, such as frequent urination or constipation, by pressing on the adjacent bladder or bowel.
Ovarian Cysts and Why They Cause Confusion
The frequent confusion regarding “cysts in the uterus” stems from the high frequency of true cysts forming on the ovaries, which are located immediately next to the uterus. Because the ovaries and uterus are structurally close, an ovarian mass is often mistakenly referred to as a uterine one. An ovarian cyst is the classic example of a true fluid-filled sac in the pelvic region.
The majority of ovarian cysts are functional cysts that develop as a normal part of the menstrual cycle. These cysts, such as follicular or corpus luteum cysts, are usually harmless, cause little discomfort, and often resolve on their own within two to three menstrual cycles. Other types include endometriomas, which are cysts filled with old blood resulting from endometriosis, and dermoid cysts, which can contain various tissues like hair or fat.
Symptoms related to ovarian cysts include a dull ache, pelvic fullness or bloating, or sometimes sharp, sudden pain. This sharp pain can occur if a cyst ruptures or causes the ovary to twist in a condition called ovarian torsion. While most are benign, their proximity to the uterus makes them the primary source of confusion when discussing pelvic masses.
Identifying and Treating Uterine and Ovarian Growths
Identification of any mass typically begins with a pelvic examination and diagnostic imaging. The most common tool is the transvaginal ultrasound, which uses sound waves to create a detailed image. This imaging can distinguish between a dense, solid mass and a fluid-filled one. In some cases, a Magnetic Resonance Imaging (MRI) scan may be used to provide a comprehensive mapping of the mass’s size and exact location.
Management strategies vary widely depending on the mass type, symptom severity, and the patient’s reproductive goals. For small, asymptomatic fibroids or functional ovarian cysts, watchful waiting is often recommended, as many resolve naturally over time. Hormonal medications may also be prescribed to manage symptoms like heavy bleeding caused by fibroids or to prevent the recurrence of some ovarian cysts.
When symptoms are severe or the mass is large, surgical intervention may be necessary. Procedures are specialized for the type of mass. Examples include a polypectomy to remove a polyp, a myomectomy to remove a fibroid while preserving the uterus, or a cystectomy to remove an ovarian cyst. The goal of treatment is to relieve discomfort and restore quality of life using the least invasive method possible.