An ovarian cyst is a fluid-filled sac that develops on or inside an ovary. These sacs are extremely common and are often a normal part of the menstrual cycle, causing no symptoms and resolving on their own. While most ovarian cysts are harmless, size is a factor healthcare providers use to determine the potential for complications. Risk increases when a cyst grows large enough to interfere with normal ovarian function or shows characteristics suspicious for a non-benign growth.
Distinguishing Functional from Pathological Cysts
The potential for a cyst to become dangerous depends more on its origin and composition than on size alone. Ovarian cysts fall into two main categories: functional and pathological. Functional cysts are physiological and form as a direct result of the normal menstrual process.
Functional cysts include follicular cysts, which develop when the follicle fails to rupture and release the egg during ovulation, swelling with fluid instead. Corpus luteum cysts form after the egg is released, when the remaining tissue seals up and fills with blood or fluid. These functional cysts are nearly always benign, temporary, and usually disappear within a few menstrual cycles.
Pathological cysts are non-functional growths arising from abnormal cell development, unrelated to the menstrual cycle. Examples include dermoid cysts, which contain various tissues like hair and fat, and endometriomas, often called “chocolate cysts.” Pathological cysts are more likely to persist, grow large, and require medical attention, though most remain non-cancerous.
Size Thresholds for Monitoring and Intervention
The specific size of an ovarian cyst acts as a guideline for monitoring and intervention, with different thresholds applying to simple (functional) and complex (pathological) cysts. For premenopausal women, simple cysts measuring less than 50 millimeters (mm) are considered physiological. They require no routine follow-up, as they are expected to resolve spontaneously and are overwhelmingly benign.
As a simple cyst grows into the moderate size range of 50 mm to 70 mm, closer monitoring is usually recommended. This often involves a follow-up ultrasound scan within three to six months to ensure the cyst is shrinking or has disappeared, confirming its functional nature. If a simple cyst persists or enlarges beyond 70 mm to 80 mm, a referral for consideration of surgical removal is commonly made.
Cysts exceeding 80 mm are often recommended for surgical intervention due to the increased risk of mechanical complications like ovarian torsion, even if they are not causing symptoms. For complex cysts, which show features like solid components or thick walls on imaging, the size threshold for concern is much lower. A complex cyst of any size, even under 50 mm, warrants a more urgent investigation due to the possibility of malignancy.
Signs of Immediate Medical Concern
While size is a factor for chronic risk assessment, acute danger is defined by the sudden onset of severe symptoms, which require immediate medical attention. The most serious immediate concerns are ovarian torsion and cyst rupture. Ovarian torsion occurs when the ovary twists around the ligaments that hold it in place, cutting off its own blood supply.
This twisting causes sudden, severe, sharp pain on one side of the lower abdomen, often accompanied by intense nausea and vomiting. Cysts larger than 50 mm are more likely to cause torsion because their size makes the ovary top-heavy and unstable. If blood flow is restricted for too long, the ovarian tissue may die, necessitating emergency surgery to save the ovary.
Cyst rupture occurs when the cyst wall tears, releasing contents into the pelvic cavity and causing sudden, sharp abdominal pain. While some ruptures are uncomplicated and resolve quickly, a rupture from a large cyst can lead to significant internal bleeding. Symptoms such as dizziness, weakness, rapid heartbeat, or signs of shock following severe pain signal a medical emergency requiring immediate evaluation and possible surgery.
Management and Treatment Options
For most small, simple cysts detected incidentally, the primary treatment is “watchful waiting,” where the cyst is monitored with follow-up ultrasounds to confirm its resolution over a few menstrual cycles. Hormonal contraceptives, such as birth control pills, may be prescribed in some cases to prevent ovulation and reduce the chance of new functional cysts forming.
If a cyst is persistently large, highly symptomatic, or displays suspicious characteristics on imaging, surgical intervention is the standard next step. The procedure is typically a minimally invasive laparoscopy, where the cyst is removed (ovarian cystectomy) through small incisions. In cases of extremely large, highly suspicious, or ruptured cysts, a traditional open surgery, known as a laparotomy, may be necessary.
If the cyst is very large or highly suspicious for malignancy, the entire ovary may need to be removed in a procedure called an oophorectomy. Treatment is highly individualized based on the cyst’s size, imaging characteristics, symptoms, and menopausal status.