An ovarian cyst is a fluid-filled sac within the ovary. Often they cause no symptoms. Ovarian cysts are common findings usually discovered incidentally on physical examination or imaging. Ovarian cysts can cause complications, including rupture, hemorrhage, and torsion, which are considered gynecological emergencies. Therefore, it is essential to promptly diagnose and treat them. Occasionally they may produce bloating, lower abdominal pain, or lower back pain. The majority of cysts are harmless. If the cyst either breaks open or causes twisting of the ovary, it may cause severe pain. This may result in vomiting or feeling faint, and even cause headaches. Most ovarian cysts are related to ovulation, being either follicular cysts or corpus luteum cysts. Other types include cysts due to endometriosis, dermoid cysts, and cystadenomas. Many small cysts occur in both ovaries in polycystic ovary syndrome (PCOS). Pelvic inflammatory disease may also result in cysts. Rarely, cysts may be a form of ovarian cancer. Diagnosis is undertaken by pelvic examination with an ultrasound or other testing used to gather further details.