An ovarian cyst is basically a pocket of fluid, like a small water balloon. If it’s a simple cyst meaning no debris floating around in the fluid and no fibrous partitions and it’s also less than 3 cm in diameter—it’s generally considered insignificant and not needing treatment or followup. Cysts less than 3 cm are also unlikely to cause pain, even if they develop rapidly.
A larger cyst can cause a lot of pain if it comes on quickly, because it will really stretch the nerve endings. If it develops slowly, it might get very big without causing any pain or other symptoms.
It’s usually called a “complex cyst” if there are particles floating around inside most often a hemorrhagic cyst because there’s been bleeding into the fluid or if it got those partitions I mentioned.
If a cyst is causing a lot of pain, they might go in laparoscopically to remove it, especially if they think the ovary might be twisted ovarian torsion. Otherwise, they usually check it again via ultrasound after 4–6 weeks – frequently, the cyst has resolved on its own. We sometimes do a blood test for CA125 to make sure we’re comfortable waiting that month and a half. @casheroo is correct that birth control pills can help it clear up. If it’s still there on recheck, then it’s time for laparoscopy so it can go to pathology. Cysts are usually benign, but if it’s persistent, you want to be sure.