Ovarian Cysts — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

An ovarian cyst is a fluid-filled sac that develops within or on the surface of an ovary. They are extremely common — up to 18% of premenopausal women have an ovarian cyst at any given time. Most ovarian cysts are functional (related to the normal menstrual cycle) and resolve spontaneously within 1-3 menstrual cycles without requiring treatment. The main types are: functional cysts — follicular cysts (from a follicle failing to rupture at ovulation — simple, thin-walled, typically less than 5 cm, usually resolve in 4-8 weeks) and corpus luteum cysts (from the post-ovulatory corpus luteum failing to resorb — can contain blood, slightly more complex, typically under 5 cm); dermoid cysts (mature teratomas — most common in women aged 20-40, may contain hair, teeth, sebum — benign but may cause torsion due to weight); endometriomas ('chocolate cysts' — from endometriosis implants on the ovary, containing old blood — associated with pelvic pain and infertility); cystadenomas (serous or mucinous — large benign epithelial tumours, can grow very large); and malignant ovarian cysts (ovarian cancer — more common in postmenopausal women; complex ultrasound features). Risk of malignancy is assessed by the Risk of Malignancy Index (RMI — combining CA-125, menopausal status, and ultrasound features).

Functional cysts: the most common ovarian cysts in premenopausal women — arise from the normal follicular development process of the menstrual cycle. A follicular cyst forms when a follicle fails to rupture and release its egg (ovulation does not occur); a corpus luteum cyst forms when the post-ovulatory corpus luteum fills with fluid or blood. Both are entirely normal physiological variants, resolving spontaneously. Risk factors for functional cysts: use of clomiphene (ovulation induction) and gonadotropin therapy in fertility treatment — which stimulates multiple follicle development (ovarian hyperstimulation syndrome). Pathological cysts: endometriomas — retrograde menstruation depositing endometrial tissue on the ovary in endometriosis; dermoid cysts (mature teratomas) — arising from germ cells capable of differentiating into multiple tissue types; cystadenomas — arising from ovarian surface epithelium; rare conditions (polycystic ovary syndrome — multiple small follicular cysts, not true ovarian cysts). Malignant ovarian cysts: risk factors for ovarian cancer include family history (BRCA1/2 mutations — 20-40% lifetime risk vs 1-2% population risk), age (rare under 40; peak incidence 63-64 years), nulliparity, hormone replacement therapy (prolonged use), endometriosis, and obesity.

Most ovarian cysts — particularly functional cysts — are asymptomatic and discovered incidentally on pelvic ultrasound performed for another reason. Symptoms when present: pelvic or lower abdominal pain — dull, aching, unilateral, often cyclical (worse with menstruation or ovulation); abdominal bloating or a sense of fullness; urinary frequency or urgency (large cysts pressing on the bladder); and deep dyspareunia (pain during intercourse). Menstrual irregularity may occur with corpus luteum cysts. Complications presenting as acute abdominal pain emergencies: Ovarian torsion (adnexal torsion): twisting of the ovary and/or fallopian tube on its pedicle — causes severe sudden-onset unilateral lower abdominal pain, often with nausea and vomiting; requires emergency surgery within 6 hours to prevent ovarian infarction. More common in cysts above 5 cm. Cyst rupture: sudden sharp pain (often at the time of ovulation or intercourse) with release of cyst contents into the peritoneal cavity — most resolve conservatively, but haemoperitoneum (bleeding from a ruptured corpus luteum cyst) may require emergency surgery. Signs suggesting malignancy: post-menopausal woman, rapid growth, complex ultrasound features, elevated CA-125, ascites, and cachexia.

Pelvic ultrasound (transvaginal ultrasound — TVS): the gold standard imaging investigation for ovarian cysts. Assesses: cyst size, laterality (left/right), characteristics (simple — unilocular, thin-walled, no solid components, anechoic fluid, no Doppler flow — very low malignancy risk; complex — multilocular, septations, solid elements, papillary projections, thick walls, Doppler flow — higher malignancy risk), and ascites. IOTA (International Ovarian Tumour Analysis) group scoring systems — Simple Rules, ADNEX model — provide validated malignancy risk stratification based on ultrasound features. Risk of Malignancy Index (RMI-1 or RMI-4): combines serum CA-125 (elevated in ovarian cancer, also endometriosis, fibroids, pelvic infection — not specific), menopausal status (premenopausal scores 1, postmenopausal scores 3), and ultrasound score. RMI above 200 — refer to cancer centre for further assessment. Serum CA-125: not reliable as a screening test in premenopausal women (multiple benign causes); more specific in postmenopausal women. MRI pelvis: provides superior soft tissue characterisation of complex cysts — particularly useful for dermoid cysts (chemical shift on T1 fat-suppressed sequences), and to clarify equivocal ultrasound findings. Blood tests: full blood count, LFTs, beta-hCG (exclude ectopic pregnancy in women of reproductive age), AFP (alpha-fetoprotein — germ cell tumours), LDH (dysgerminoma), CEA (mucinous tumours). Laparoscopy: for definitive diagnosis and treatment of complex or suspicious cysts.

Simple functional cysts in premenopausal women (less than 5 cm, thin-walled, unilocular): no treatment required — reassure and repeat ultrasound at 6-8 weeks; most resolve spontaneously. Simple cysts 5-7 cm: annual ultrasound surveillance. All complex or uncertain cysts: gynaecology review. RCOG guidelines (2011, Green-top Guideline 62): simple unilocular cysts under 5 cm in postmenopausal women — annual ultrasound plus CA-125 surveillance for 1 year; simple cysts over 7 cm in any woman — surgical assessment or MRI (large cysts are at risk of torsion). Combined oral contraceptive pill (COCP): does not accelerate resolution of existing functional cysts but may prevent new ones in women with recurrent functional cysts. Surgical management — indications: symptomatic cysts (pain, pressure), cysts not resolving on surveillance, complex or malignant features on imaging, cysts over 5-7 cm (torsion risk), dermoid cysts (laparoscopic cystectomy — shelling out the cyst from the ovary preserving normal ovarian tissue), endometriomas (laparoscopic drainage and diathermy — however, risk of reducing ovarian reserve; discuss in context of fertility). Laparoscopic approach: preferred for most benign cysts — shorter recovery, less adhesion formation. Open surgery (laparotomy): for large cysts (risk of rupture and spillage with laparoscopy), suspected malignancy, or where laparoscopic approach is not feasible. If ovarian malignancy is confirmed: staging laparotomy (peritoneal sampling, omentectomy, lymph node assessment) and adjuvant chemotherapy (platinum-based — carboplatin plus paclitaxel) at a gynaecological oncology centre. Emergency surgery for ovarian torsion: laparoscopic de-torsion within 6 hours (ovary can often be untwisted and preserved if done promptly, even if it appears congested); cystectomy if a cyst is present. Cyst aspiration alone is not recommended — high recurrence rate and risk of cyst rupture.

Ovarian torsion is the most serious acute complication — twisting of the ovary and fallopian tube on its vascular pedicle causes ischaemic infarction if surgery is not performed within 6 hours of onset. It occurs more commonly with cysts above 5 cm. Irreversible ovarian loss occurs if detorsion is delayed — preserving the ovary requires urgent laparoscopic surgery even if the ovary appears ischaemic at the time. Cyst rupture causes peritoneal irritation from follicular fluid and, if the cyst contains blood (haemorrhagic corpus luteum cyst), may cause haemoperitoneum requiring emergency surgery. Endometriomas progressively damage ovarian cortical tissue and reduce ovarian reserve over time, impairing fertility even before surgical intervention. The most clinically important long-term complication of complex ovarian cysts is malignancy — approximately 15% of complex ovarian masses in postmenopausal women are found to be malignant on histopathology. Missed or delayed diagnosis of ovarian cancer significantly worsens staging and prognosis. Adhesion formation from recurrent cysts or previous surgery can impair tubal function and fertility.

Functional ovarian cysts cannot be reliably prevented — they are part of the normal menstrual cycle in most cases. Combined oral contraceptive pill (COCP): suppresses ovulation and reduces the formation of new functional cysts (follicular and corpus luteum cysts) — the COCP does not treat existing cysts but may be considered for women with recurrent functional cysts. Endometrioma prevention: prompt diagnosis and treatment of endometriosis reduces the formation of new endometriomas; laparoscopic excision of endometriomas (rather than drainage alone) reduces recurrence. Ovarian cancer risk reduction: BRCA1/2 carriers — risk-reducing bilateral salpingo-oophorectomy (RRSO) at 35-40 years (BRCA1) or 40-45 years (BRCA2) dramatically reduces ovarian cancer risk; COCP use reduces ovarian cancer risk by 30-50% with 5 or more years of use (protective effect persists for years after stopping). Healthy weight, regular physical activity, and avoidance of prolonged post-menopausal HRT may modestly reduce ovarian cancer risk. Awareness of symptoms: pelvic bloating, early satiety, urinary symptoms, and pelvic pain in postmenopausal women should prompt urgent GP assessment — ovarian cancer is often diagnosed late as early symptoms are non-specific.

See a GP if you experience persistent pelvic or lower abdominal pain, bloating, or urinary symptoms that could be related to an ovarian cyst. Seek immediate emergency care (call 999 or go to A&E) for: sudden severe unilateral lower abdominal pain with nausea and vomiting — this may indicate ovarian torsion (a gynaecological emergency requiring surgery within 6 hours to save the ovary); sudden sharp pelvic pain with cardiovascular instability (dizziness, faintness, heavy bleeding) suggesting a ruptured corpus luteum cyst with haemoperitoneum. GP referral is urgently required (2-week wait pathway) for postmenopausal women with pelvic symptoms, new abdominal distension or bloating, elevated CA-125, or a complex ovarian mass on ultrasound. All women with a known ovarian cyst should attend follow-up imaging as recommended — do not miss surveillance appointments. Any woman with BRCA1/2 gene mutations should be enrolled in cancer surveillance and discuss preventive surgery with a gynaecological oncologist.