Ovarian cysts, torsion and benign ovarian tumours

• Most ovarian cysts in women of reproductive age are functional (follicular or corpus luteum) cysts, are benign, and resolve on their own within a few menstrual cycles. ^[6]
• Benign non-functional cysts include dermoid cysts, endometriomas, haemorrhagic cysts and other benign tumours; each has predictable ultrasound features.
• Adnexal (ovarian) torsion is a surgical emergency: sudden unilateral pelvic pain with nausea and vomiting, often with an ovarian mass, treated by prompt laparoscopy with detorsion rather than oophorectomy. ^[1]
• Transvaginal ultrasound is the first investigation in almost every case; the ACR O-RADS ultrasound system turns its features into a risk of malignancy and a management plan.
• Operation is reserved for suspected malignancy, torsion, rupture with haemorrhage, a large cyst, or symptoms that do not settle; fertility is preserved whenever possible.

By the end of this page you should be able to:

1. Describe how a functional cyst forms, why it is usually self-limiting, and when it needs treatment.
2. Recognise an endometrioma and a dermoid cyst on ultrasound and state their main complications.
3. Recognise a haemorrhagic cyst and outline its short-interval follow-up.
4. Explain the presentation of adnexal torsion and why detorsion with conservation of the ovary is the standard operation.
5. Use the six O-RADS ultrasound categories and the classic benign lesion tables to assign a risk of malignancy and a follow-up plan.
6. Apply the RCOG and ACOG approaches to suspected ovarian masses in premenopausal and postmenopausal women.

The adult ovary is part of a cyclic system. Each month a follicle enlarges and, after ovulation, the corpus luteum forms. Most cysts are simply exaggerations of these normal structures. A minority are true neoplasms, most of them benign, and a small number are malignant. Because the first question for any adnexal mass is "could this be cancer?", the page keeps two things in tension throughout: the reassuring natural history of functional cysts, and the need to exclude malignancy in persistent or complex masses. The current guidelines most often cited are ACOG Committee Opinion No. 783 for adolescent torsion ^[1], RCOG Green-top Guideline No. 62 for suspected ovarian masses in premenopausal women ^[2], and the ACR O-RADS ultrasound system version 2022 ^[4]. ^[5]

An ovarian cyst is a fluid-containing structure within or arising from an ovary. An adnexal mass is the wider term and includes masses of the fallopian tube, paraovarian tissues and, occasionally, other pelvic organs. Ovarian cysts are not one disease; they fall into broad groups:

• Functional (physiologic) cysts, produced by the normal cycle: follicular cysts and corpus luteum cysts.
• Haemorrhagic cysts, which are functional cysts into which bleeding has occurred.
• Endometriomas, from endometriosis.
• Dermoid cysts (mature cystic teratomas), the commonest benign neoplastic cyst of reproductive life.
• Other benign cystic tumours, such as serous and mucinous cystadenomas.
• Borderline and malignant tumours, which must be excluded in any persistent or complex mass.

In the ACR O-RADS ultrasound system a cyst is "physiologic" (O-RADS 1) only if it is a normal follicle of 3 cm or less, or a corpus luteum of about that size, in a premenopausal woman ^[7]. Everything else is a lesion that must be characterised.

Benign cysts are extremely common: most women of reproductive age have at least one cyst detected incidentally at some point, and most of these are functional and resolve without treatment. A broad epidemiological estimate is that about one in five women develops a pelvic mass during life, without implying malignancy ^[5]. Simple cysts are the most likely type in every age group. Their importance rises after the menopause, because the prior probability of malignancy is higher in older women, which is why any cyst in a postmenopausal woman is followed more cautiously ^[5].

• Age pattern. Functional cysts predominate between puberty and menopause. In adolescents, a normal-sized ovary may itself undergo torsion in as many as 46% of torsion cases, so that torsion is not always caused by a large mass ^[1].
• Malignancy overall is uncommon. Most adnexal masses are benign in all age groups; the purpose of evaluation is to find the minority that are not.

Functional cysts arise from the cycle itself: a follicle that does not rupture, or a corpus luteum that does not involute, continues to grow under hormonal drive ^[5]. Risk factors include ovulation-inducing agents, smoking, pregnancy, hypothyroidism and tubal ligation, all of which can produce persistent cysts ^[5].

Endometriomas are caused by endometriosis: ectopic endometrial tissue bleeds into the ovary, producing a haemorrhagic cyst filled with dark brown endometrial fluid, the classic "chocolate cyst."

Dermoid cysts are germ-cell tumours containing well-differentiated tissues from all three germ layers (ectoderm, mesoderm and endoderm), which is why they may contain hair, fat, teeth or bone.

Haemorrhagic cysts usually represent bleeding into a corpus luteum or another functional cyst.

Other recognised risk factors for adnexal masses include a family history of breast, ovarian or bowel cancer, a personal history of endometriosis, prior pelvic surgery and pelvic inflammatory disease.

Follicular cysts start when the usual mid-cycle luteinising hormone surge does not trigger rupture of the follicle. The follicle keeps enlarging beyond 2.5 cm and keeps producing oestrogen, which can suppress menstruation ^[5]. Corpus luteum cysts form when the corpus luteum fails to regress, or bleeds into its cavity. Both are therefore exaggerations of normal structures, which is why most regress when the hormonal drive changes.

Endometriomas are not simple cysts at all: repeated cycles of bleeding into the ovary produce haemosiderin-laden fluid and a fibrous wall, so they feel firm and look like ground-glass echoes on ultrasound.

Dermoid cysts grow slowly from retained embryonic tissue and are present for years before they are found.

Haemorrhagic cysts evolve as blood organises: fibrin strands form a reticular "cobweb" pattern and a clot retracts, producing the classic ultrasound appearance.

Torsion occurs when a mass is heavy enough, or ligaments long enough, to let the ovary rotate on its pedicle. The venous and lymphatic outflow is obstructed first, so the ovary becomes swollen and cyanotic; arterial flow is lost later. This order matters clinically, because Doppler can still show arterial flow in an early torsion.

Many cysts are silent. Functional, dermoid and endometriomal cysts are frequently found incidentally at ultrasound done for another reason, for menstrual problems, or for subfertility.

Benign cysts needing little urgent action. A small, simple cyst may cause no symptoms at all, or a vague low pelvic ache, heaviness or pressure symptoms from a large mass.

Endometrioma. Pelvic pain, dysmenorrhoea, deep dyspareunia and subfertility are typical, and the cyst is usually an incidental ultrasound finding on top of known endometriosis.

Torsion. This is the emergency presentation and should be recognised on clinical grounds, because imaging is useful but never conclusive ^[1]:

• sudden-onset, severe, intermittent, non-radiating unilateral lower abdominal or pelvic pain, often with nausea and vomiting; ^[1]
• an adnexal mass or fullness on examination, or a normal examination;
• episodes that settle and recur (intermittent torsion);
• in about half of adolescents, an ovary without an associated mass or cyst ^[1].

Rupture or haemorrhage. Sudden pain with haemodynamic upset in a woman with a known or suspected cyst; many cases are mild and settle with analgesia.

Examination should look for a palpable pelvic mass, tenderness, signs of peritonism, tachycardia and pallor. A pregnancy test is mandatory in every woman of reproductive age.

The clinical problem is usually to decide whether a cyst is physiologic/benign, torsed, haemorrhagic or malignant.

Pregnancy (including ectopic pregnancy) is excluded in every woman of reproductive age before attributing bleeding or pain to a cyst ^[2][5].

Transvaginal ultrasound is the single most effective test for an adnexal mass, performed with a description of site, size, internal contents, wall and septations, vascularity and ascites ^[5]. Abdominal ultrasound is added when anatomy is distorted or a mass is too large for the transvaginal probe ^[5]. A simple cyst of 10 cm or less in any woman is highly likely to be benign, with a malignancy rate below 1% ^[5].

Ovarian reserve and hormonal status (oral contraceptives, hormone therapy) should be known at the time of scanning ^[5].

The ACR O-RADS ultrasound system (2019 version, updated version 2022) converts ultrasound features into a numeric risk of malignancy and a management recommendation ^[3][4][7]. It applies whenever a non-physiologic adnexal lesion is found, and it is built on the IOTA-based lexicon of descriptors. The categories are summarised below; the full lexicon and the version 2022 changes are in the referenced papers and the harmonised teaching tables ^[4][7].

Three common cyst types have "classic" appearances that put them in O-RADS 2 when smaller than 10 cm, each with its own management rule ^[5][7]:

• Haemorrhagic cyst. Unilocular, avascular, with a reticular ("cobweb") pattern and/or a retractile clot with straight or concave margins. Premenopausal: 5 cm or less needs no follow-up; 5 to 10 cm needs an ultrasound in 2 to 3 months. Early postmenopausal (under 5 years): ultrasound in 2 to 3 months, or expert scan or MRI. Late postmenopausal: should not occur; reassess with other descriptors ^[7].
• Dermoid cyst. Up to 3 locules with no internal vascularity plus hyperechoic component(s) with shadowing, hyperechoic lines and dots, or floating echogenic spheres. If not excised, ultrasound at about 12 months (May consider ultrasound in 12 months even for 3 cm or less) ^[7].
• Endometrioma. Up to 3 locules, no internal vascularity, homogeneous low-level "ground-glass" echoes with smooth walls; punctate wall foci are highly characteristic. Premenopausal: 12-month follow-up if not excised. Postmenopausal: confirm (ultrasound in 2 to 3 months, expert scan, or MRI) then 12-month follow-up ^[5][7].

A classic cyst that does not resolve or that changes at follow-up should be reclassified using other descriptors rather than labelled "typical" ^[5].

In a postmenopausal woman an ovarian cyst should first be assessed with serum CA125 together with transvaginal ultrasound ^[5]. CA125 is raised in about 85% of epithelial ovarian cancers; in stage I disease it may be raised in only half ^[5]. The normal value is taken as less than 35 U per mL ^[5]. It should never be used on its own to diagnose or exclude cancer. It is less useful in premenopausal women, in whom benign conditions (endometriosis, fibroids, menstruation) raise it.

Where ultrasound suggests possible malignancy, a risk of malignancy index helps triage. Prefer the RMI I version, where a score of 200 (sensitivity about 78%, specificity about 87%) predicts a higher chance of cancer and should prompt referral, although some centres use an equally acceptable threshold of 250 with lower sensitivity (about 70%) and higher specificity (about 90%) ^[5]. CT of the abdomen and pelvis is recommended when the RMI is 200 or above and confirms the need for a gynaecological oncology multidisciplinary assessment; CT, MRI and PET are not recommended for the initial evaluation of a simple cyst ^[5].

Ultrasound features that should raise concern for malignancy are cyst size over 10 cm, solid or papillary components, irregularity, septations of 3 mm or more, ascites and high colour Doppler flow ^[5]. Where a mass is indeterminate, short-interval follow-up (6 to 12 weeks) in a menstrual phase appropriate part of the cycle, or MRI, helps; in postmenopausal women an indeterminate mass should be considered for surgical evaluation ^[5].

There is no single "positive" test for a typical benign cyst. Instead we combine age, menopausal status, ultrasound morphology (and O-RADS category), rate of change and, in postmenopausal women, CA125 or RMI. The key cut-offs are:

• Simple cyst 10 cm or less in any woman is highly likely benign (below 1% malignancy) ^[5].
• A normal CA125 of less than 35 U per mL does not exclude cancer in a postmenopausal woman ^[5].
• Endometrioma or dermoid 10 cm or larger, or with internal vascular flow, changes risk, and malignancy in such cysts usually occurs in women older than 45 to 50 years ^[5].
• Torsion is a clinical diagnosis with imaging support; no ultrasound sign alone excludes it ^[1].

Most cysts need no emergency care. The emergencies are torsion (below), rupture with haemodynamic compromise, and severe pain in pregnancy.

Premenopausal women. The RCOG Green-top Guideline No. 62 (2011, second edition in development) addresses suspected ovarian masses in premenopausal women and provides a framework for deciding which can stay in benign gynaecology and which need a gynaecological oncologist ^[2]. Confirm the mass is real with a good-quality transvaginal ultrasound and exclude pregnancy and non-ovarian causes of pain. Most small simple cysts are physiologic and settle within three menstrual cycles.

Expectant management is usually correct:

• a simple cyst under 3 cm in a premenopausal woman is a physiologic finding that needs no follow-up;
• a small cyst above 3 cm and up to 7 cm is almost certainly benign and can be followed with ultrasound until stability is shown;
• keep CA125 for postmenopausal women or when malignancy is suspected.

If a cyst persists or grows after several cycles it is unlikely to be functional and needs further evaluation (MRI or surgical evaluation).

The clot and fibrin resolve with the cycle, so a classic haemorrhagic cyst in a premenopausal woman up to 5 cm needs no follow-up, and 5 to 10 cm needs an ultrasound in 2 to 3 months to confirm resolution ^[7]. In early postmenopause (under 5 years), confirm within 2 to 3 months with ultrasound, an expert scan or MRI. Reassess anything that persists ^[5][7].

Dermoids are benign but slow-growing and, importantly, are the ovarian mass most likely to undergo torsion. They should generally be followed with ultrasound about every 12 months if not removed ^[5][7]. Surgical removal is warranted if the cyst is large (a dermoid replacing most of the ovary, or over 5 to 6 cm), if it causes symptoms, if it is growing, or if malignancy cannot be excluded ^[5]. In premenopausal women, laparoscopic ovarian cystectomy is preferred over removing the whole ovary; oophorectomy is reserved for postmenopausal women or when the cyst has replaced the ovary ^[5].

Malignant change occurs in only 0.17% to 2% of dermoids, is almost always squamous cell carcinoma, and tends to affect women over 50 years with cysts larger than 10 cm (case reports down to 3 cm exist) ^[5]. Torsion is the commoner acute risk.

Diagnosis is usually by the characteristic ultrasound appearance, ideally by a scan specialist. Management depends on symptoms, plans for pregnancy and cyst size:

• Asymptomatic and small: follow with ultrasound (12-monthly if stable) and treat the underlying endometriosis ^[5].
• Pain or subfertility in a woman who wishes to conceive: laparoscopic ovarian cystectomy, not simple drainage and coagulation, is the operation that reduces recurrence of both the cyst and pain ^[5].
• Recurrence is common; as many as 1% of endometriomas undergo malignant transformation, usually endometrioid or clear cell carcinoma, especially in women over 45 years and in cysts larger than 9 cm ^[5].
• Delaying surgery in endometriosis is common practice; surgery before assisted reproduction is not routinely offered unless there is pain or follicle access is impaired.

Secondary prevention after cystectomy uses at least 18 to 24 months of a levonorgestrel-releasing intrauterine system or combined hormonal contraception when pregnancy is not wanted, and long-term combined hormonal contraception thereafter, to suppress recurrence ^[5].

Hormonal suppression (combined hormonal contraception, progestogens, a levonorgestrel intrauterine system, or GnRH agonists or antagonists) is first-line for endometriosis-associated pain, with surgery reserved for women who do not respond or who want pregnancy ^[5].

Adnexal torsion is the fifth most common gynaecological emergency ^[1]. The management is based on clinical suspicion and rapid laparoscopy.

Points from the ACOG guideline that drive practice: torsion is more likely with benign functional cysts and mature teratomas; malignancy is rare in these patients ^[1]. A surgeon should not remove a torsed ovary in a reproductive-age woman unless it is unavoidable; preservation is the standard even when the ovary appears necrotic ^[1]. Histology of a necrotic ovary shows true necrosis in only 18% to 20% of such cases, and normal follicular activity is seen on ultrasound after surgery ^[2].

Masses suspicious for malignancy, complex indeterminate cysts in postmenopausal women, persistent cysts over 7 to 10 cm and symptomatic cysts generally proceed to surgery. Round and slow; preserve fertility until the diagnosis is clear:

• simpler masses: benign gynaecology (laparoscopic approach preferred);
• suspected malignancy: gynaecological oncology after staging CT;
• salpingectomy or opportunistic salpingectomy can be added where malignancy is not suspected and the woman is near menopause.

Intra-abdominal spillage of cyst contents should be avoided, particularly for dermoids.

Follow-up rules come from the SRU consensus and O-RADS ^[5][7]:

• Simple cysts: premenopausal 5 cm and under need no follow-up; 5 to 7 cm yearly until stable; over 7 cm deserves MRI or surgical evaluation. Postmenopausal: 1 cm and under no follow-up; 1 to 7 cm yearly, at least initially. ^[5]
• Haemorrhagic, dermoid and endometrioma cysts: follow-up as above in the O-RADS table.
• Dermoids and endometriomas: at least yearly until surgically removed, or longer intervals once stability is assured.

Torsion is diagnosed late and ovaries are lost when it is mistaken for appendicitis or infection. Simple clinical vigilance and prompt laparoscopy save more tissue than sophisticated imaging. Where ultrasound quality is poor, a Doppler study can be misleading; treat on clinical grounds. If complex imaging is unavailable, a clean history, free-fluid on bedside ultrasound, a pregnancy test and an urgent laparoscopy are the whole protocol.

• Torsion (most serious acute complication of an ovarian cyst), with ischaemia and loss of the ovary if delayed.
• Rupture and haemorrhage, usually of a functional or haemorrhagic cyst; most cases are self-limiting.
• Malignant transformation in a minority of dermoids and endometriomas (percentages above); this argues for follow-up and removal of persistent complex masses.
• Infertility, particularly from endometriomas and from repeated surgery.
• Recurrence of functional cysts if the underlying cause (such as ovulation induction) persists; endometriomas recur frequently without hormonal suppression.

The prognosis of a functional or typical benign cyst is excellent: most resolve without treatment. Dermoids, endometriomas and cystadenomas are cured by resection; recurrence depends on completeness of excision. Adnexal torsion treated promptly with detorsion retains ovarian function in most women.

There is no routine screening for ovarian cysts. Regular gynaecological review, early treatment of endometriosis, fertility-preserving counselling and avoidance of unnecessary surgery are the practical preventive measures. Recurrence of functional cysts is reduced by treating ovulation disorders.

• Adolescents. Torsion is not always associated with a mass (up to 46%) ^[1]. Detortion with conservation is always attempted first; cystectomy is deferred if the ovary is very oedematous. Ovulation suppression reduces recurrent functional cysts.
• Pregnancy. Most pregnancy-related cysts are corpus luteal or follicular and resolve by 14 to 16 weeks' gestation; cysts over 5 cm or with complex morphology are less likely to resolve ^[5]. Surgery, if needed, is safest in the second trimester. Torsion is more common in pregnancy and early postpartum.
• Postmenopausal women. Any cyst needs CA125 and ultrasound, and persistent or complex masses need surgical evaluation because the risk of malignancy is higher.
• Fertility. Preserve ovarian tissue wherever possible in premenopausal women, even in apparently necrotic ovaries.

• Suspected torsion or severe acute pelvic pain with adnexal mass should go the same day to gynaecology for diagnostic laparoscopy.
• Haemodynamic instability, suspected ectopic pregnancy or severe intra-abdominal bleeding.
• Suspicion of malignancy (solid or papillary elements, high Doppler flow, ascites, elevated RMI, or age over 45 with complex mass).
• Persistent cyst over 7 to 10 cm, or one that is growing on follow-up.
• Endometrioma with significant pain or subfertility.
• Any mass in a postmenopausal woman that is suspicious or that persists at follow-up.

• Most ovarian cysts in reproductive life are functional, benign and self-limiting.
• An ovarian mass present for more than a few cycles is unlikely to be functional and needs evaluation.
• Transvaginal ultrasound first; it separates simple, classic benign and suspicious masses better than any other test.
• A simple cyst of 10 cm or less has a malignancy rate below 1%.
• CA125 is used with ultrasound in postmenopausal women; a normal result does not exclude cancer.
• Use O-RADS to convert morphology into a risk of malignancy and a plan.
• Dermoids are followed about yearly; endometriomas are followed similarly and resected for pain or fertility.
• Haemorrhagic cysts of under 5 cm in premenopausal women need no follow-up; 5 to 10 cm needs an ultrasound in 2 to 3 months.
• Endometrioma malignancy occurs in about 1% of cases, usually in women over 45 years with cysts above 9 cm.
• Dermoid malignant change occurs in 0.17% to 2%, usually over 50 years and 10 cm or larger. ^[5]
• Adnexal torsion is a clinical emergency: sudden pain with nausea and vomiting, and 46% of adolescents have an apparently normal-sized ovary involved.
• Treat suspected torsion with prompt laparoscopy, detorsion and conservation of the ovary; remove only if the ovary disintegrates.
• A dark, oedematous ovary usually recovers; preservation is the standard.

Benign and malignant adnexal masses, endometriosis, ovarian cancer, menstrual disorders, contraception and intrauterine systems, infertility, pelvic pain and acute abdomen, and gynaecological ultrasound. These corresponding MedGrasp pages are listed by name only until they are verified.