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Health condition · Clinically reviewed

Ovarian cyst, ultrasound assessment - and when surgery is actually needed.

Most ovarian cysts are harmless and settle on their own. A clear scan-led pathway tells the few that need attention from the many that don’t.

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A radiographer guides a patient onto the bed of an advanced 3 Tesla MRI scanner in a London imaging suite

Why trust this guide

  • 01

    Clinically reviewed

    Written by our editorial team and reviewed by a registered UK clinician before publication.

  • 02

    Sourced from guidance

    Checked against the RCOG Green-top Guideline and peer-reviewed sources you can see at the end.

  • 03

    Current for 2026

    Reflects modern UK practice - transvaginal ultrasound, the Risk of Malignancy Index and stepped surgical care.

Key facts

Ovarian cysts at a glance.

The essentials, in plain English - what a cyst is, the main types, and how it’s assessed in the UK today.

  • What it is

    A fluid-filled sac on or within the ovary - extremely common and, in most cases, entirely benign.

  • Most common type

    Functional cysts (follicular or corpus luteum) are physiological and usually resolve on their own within a few cycles.

  • Other types

    Endometriomas ("chocolate cysts"), dermoid cysts and, rarely, malignant cysts each need a different approach.

  • Key investigation

    Transvaginal pelvic ultrasound - the central tool for characterising size, structure and risk.

  • Risk scoring

    CA125 plus ultrasound findings feed into the Risk of Malignancy Index (RMI), especially in postmenopausal women.

  • Main management

    Watchful waiting for most simple cysts - surgery reserved for large, persistent, symptomatic or suspicious ones.

Why this guide matters

A scan-led pathway, not needless worry.

Ovarian cysts are common and mostly benign - but the right assessment matters. The three points below shape everything else on this page.

  • Most cysts resolve on their own

    Functional cysts are physiological, not pathological - watchful waiting with a repeat scan is often all that’s needed.

  • Ultrasound does most of the work

    Transvaginal ultrasound characterises the vast majority of cysts without the need for further imaging or surgery.

  • A minority need urgent action

    Torsion, rupture and suspicious features are uncommon but time-critical - knowing the red flags protects you.

How the diagnosis is made

From an incidental finding to a clear plan.

The steps a UK GP or gynaecologist will normally follow, per RCOG guidance - so you know what to expect and why.

  1. 01

    Assessing

    Symptom and risk-factor history

    Pain pattern, cycle timing, menopausal status and family history of ovarian or breast cancer all shape the next step.

  2. 02

    Assessing

    Abdominal and pelvic examination

    A clinician feels for a palpable mass, tenderness or signs of peritonism that might suggest torsion or rupture.

  3. 03

    Confirming

    Transvaginal pelvic ultrasound

    The key diagnostic tool per RCOG guidance - assessing size, whether the cyst is simple or complex, and its likely nature.

  4. 04

    Confirming

    CA125 and the RMI

    CA125 is checked when there are suspicious features, particularly in postmenopausal women, and combined with ultrasound findings to calculate the Risk of Malignancy Index.

  5. 05

    Confirming

    Assessment for torsion or rupture

    Sudden severe pain, guarding or signs of shock prompt immediate clinical assessment and same-day emergency referral.

  6. 06

    Planning

    Size and characteristics guide follow-up

    Small simple cysts in premenopausal women are usually followed with a repeat scan; larger or complex cysts move toward gynaecology review.

  7. 07

    Planning

    Gynaecological oncology referral

    An elevated RMI or suspicious ultrasound features trigger referral to a specialist gynaecological oncology multidisciplinary team.

Typical timeline: a first scan to a settled plan within a few weeks.

Symptoms

What an ovarian cyst actually feels like.

Many cysts cause nothing at all. Others bring pain, bloating or cycle changes - and a few present as an emergency.

  • Often no symptoms

    Many ovarian cysts are found incidentally on a scan done for another reason and cause no problems at all.

  • Pelvic pain or discomfort

    A dull, persistent ache low in the abdomen or pelvis, usually on one side, is the most common complaint.

  • Bloating

    A feeling of fullness or visible abdominal swelling, sometimes worse as the day goes on.

  • Irregular periods

    Hormonally active cysts can disturb the normal cycle - heavier, lighter or less predictable bleeding.

  • Pain during intercourse

    Deep pain during sex, often worse in certain positions, can point to a cyst pressing on nearby structures.

  • Sudden sharp pain - rupture

    A cyst that ruptures can cause sudden, sharp one-sided pain, sometimes with light vaginal bleeding.

  • Ovarian torsion - an emergency

    Severe, sudden pelvic pain with nausea and vomiting suggests the ovary has twisted on its blood supply.

  • Red flag - call 999 or go to A&E

    Sudden, severe pelvic pain, especially with fever, vomiting or fainting, needs emergency assessment straight away.

Treatment

How ovarian cysts are managed in the UK.

Watchful waiting for most, surgery for those that are large, persistent, symptomatic or suspicious - and emergency care when needed.

  • Watchful waiting

    For small simple cysts in premenopausal women - many resolve spontaneously and are followed with a repeat ultrasound.

  • Pain relief

    Simple analgesia manages discomfort while a cyst is monitored or awaiting a decision on surgery.

  • Laparoscopic cystectomy

    Keyhole removal of the cyst while preserving healthy ovarian tissue - the standard approach for persistent or symptomatic benign cysts.

  • Oophorectomy

    Removal of the affected ovary - considered for large, complex or recurrent cysts, or in postmenopausal women.

  • Emergency surgery

    Urgent laparoscopy or laparotomy for suspected torsion or a ruptured cyst with significant internal bleeding.

  • Gynaecological oncology referral

    Any cyst with an elevated Risk of Malignancy Index is managed jointly with a specialist cancer multidisciplinary team.

  • Hormonal contraception

    The combined pill can reduce the chance of new functional cysts forming, though it does not shrink an existing one.

  • Post-treatment follow-up

    A clear plan for symptom review, histology results where relevant, and further scans if needed.

What this guide is based on

The sources behind every claim on this page.

UK national guidance and specialist society standards, current at the time of last review.

Key references

Guidelines and standards we relied on.

A quiet reminder

This guide is for information, not medical advice.

Your GP or gynaecologist knows your history and scan findings and can tell you which parts apply to you. If in doubt, get seen.

  • Royal College of Obstetricians and Gynaecologists (RCOG). Green-top Guideline: Management of Suspected Ovarian Masses in Premenopausal Women.

  • RCOG / British Society for Gynaecological Endoscopy. Ovarian cysts in postmenopausal women.

  • NICE. Ovarian cancer: recognition and initial management (CG122) and suspected cancer referral guidance (NG12).

  • International Ovarian Tumour Analysis (IOTA) group. Ultrasound-based risk stratification of adnexal masses.

Red flags

When an ovarian cyst needs urgent attention.

Most ovarian cysts are manageable in primary care. These are the situations that aren’t - and where urgent or specialist care is needed.

  • Suspected ovarian torsion

    Sudden, severe one-sided pelvic pain with nausea and vomiting is a surgical emergency - call 999 or go straight to A&E.

  • Cyst rupture with bleeding

    Sharp pain with signs of internal bleeding - light-headedness, a racing pulse or fainting - needs immediate emergency care.

  • Elevated Risk of Malignancy Index

    A high RMI from combined ultrasound and CA125 findings warrants urgent referral to gynaecological oncology.

  • Complex cyst after the menopause

    Any complex or growing adnexal mass in a postmenopausal woman is treated with a lower threshold for specialist review.

  • Ascites with a pelvic mass

    Fluid in the abdomen alongside an ovarian mass is a recognised marker of possible malignancy and needs prompt investigation.

  • Rapid abdominal distension

    A cyst or mass that is growing quickly, or causing rapid swelling, should be assessed without delay.

  • Signs of hypovolaemic shock

    Pale, clammy skin, a fast weak pulse or breathlessness after sudden pelvic pain suggests significant internal bleeding.

  • Persistent cyst over 5cm

    A simple cyst that has not resolved on repeat scanning, or is enlarging, usually merits gynaecology review.

  • Strong family history

    A family history of ovarian or breast cancer, including BRCA mutation carriers, changes the threshold for referral and testing.

Living with it

A common finding, with a clear path forward.

Four things that make the biggest difference while a cyst is being watched or treated - tracking symptoms, attending follow-up, knowing the emergency signs and pacing yourself.

A quiet reminder

Most cysts are watched, not worried about.

A repeat scan and a little patience resolves the majority of simple cysts without any surgery at all.

  1. 01 Track

    Keep a symptom diary

    Note when pain occurs relative to your cycle - it helps your clinician tell a functional cyst from something else.

  2. 02 Follow-up

    Attend your repeat scan

    Most simple cysts are followed with a scan in 6 to 12 weeks - this confirms resolution and avoids unnecessary surgery.

  3. 03 Recognise

    Know the emergency signs

    Sudden severe pain, fainting or fever after a known cyst means going to A&E, not waiting for a routine appointment.

  4. 04 Manage

    Pace activity and pain relief

    Simple analgesia and avoiding activities that aggravate discomfort help while a cyst is being monitored.

Frequently asked

Everything we get asked about ovarian cysts.

Quick answers on cancer risk, CA125, rupture, torsion and fertility.

  • What is an ovarian cyst?

    A fluid-filled sac that forms on or within the ovary. Most are functional cysts related to the normal menstrual cycle and resolve on their own, though other types such as endometriomas, dermoid cysts and, rarely, malignant cysts also occur.

  • Are ovarian cysts usually cancerous?

    No - the great majority of ovarian cysts, particularly in premenopausal women, are benign. Ultrasound features and CA125 are used together in the Risk of Malignancy Index to identify the small number that need specialist review.

  • Do all ovarian cysts need treatment?

    Not at all. Small, simple functional cysts in premenopausal women are usually managed with watchful waiting and a repeat scan, since many resolve spontaneously within a few menstrual cycles.

  • What does a CA125 blood test tell you?

    CA125 is a tumour marker that can be raised with ovarian cysts, endometriosis and several benign conditions, so it is interpreted alongside ultrasound findings rather than on its own - particularly important in postmenopausal women.

  • What happens if a cyst ruptures or the ovary twists?

    Both are emergencies. A ruptured cyst can cause sudden pain and internal bleeding, while ovarian torsion cuts off the ovary’s blood supply and needs urgent surgery. Sudden severe pelvic pain should always prompt emergency assessment.

  • Can ovarian cysts affect fertility?

    Most simple cysts do not affect fertility. Endometriomas and surgery to remove a cyst can reduce ovarian reserve to some degree, which is why fertility-preserving techniques are used whenever appropriate.

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