Ovarian cyst found by chance: follow-up scans
An ovarian cyst is a sac filled with fluid on or inside an ovary, and it may be found on an ultrasound done for another reason. (MedlinePlus) ACOG says most adnexal masses (on the ovary, fallopian tube or nearby tissue) are found by chance on an exam or pelvic scan, and most are benign. (ACOG PB 174) This page covers which cysts get repeat scans and when, not surgery or treatment.
The main guidance
- O-RADS US (American College of Radiology): scores ovarian and adnexal lesions from 0 to 5 by their look on ultrasound, with a risk of cancer and a follow-up plan for each score. Version 2022 added more benign features and says lower-risk score 3 lesions can be watched with ultrasound. (O-RADS US v2022)(Strachowski 2023)
- SRU 2019 consensus (Society of Radiologists in Ultrasound): follow-up and reporting sizes for simple cysts, based on studies showing a very low risk of cancer. (SRU 2019)
- RCOG Green-top Guidelines (UK): No. 34 for cysts after menopause (2016, minor update December 2025) and No. 62 for ovarian masses before menopause (2011). (RCOG GTG 34)(RCOG GTG 62)
Who it applies to
The SRU sizes apply to people with no symptoms, or whose symptoms are not clearly caused by the cyst. (SRU 2019) The SRU, O-RADS and ACR guidance on cysts found by chance applies to people who are not pregnant and are at average risk of ovarian cancer. (Wang 2022) O-RADS counts a person as after menopause after 1 year or more without periods; if that is unclear, or the uterus has been removed, it uses age over 50. (O-RADS US v2022) For a family history or a gene change, see ovarian cancer screening.
The O-RADS US scores
| Score | Risk of cancer | Usual next step |
|---|---|---|
| 0 | Incomplete scan | Repeat ultrasound or MRI |
| 1 | Normal ovary, or a follicle or corpus luteum (usually 3 cm or less) | None |
| 2 | Almost certainly benign (under 1%) | None, or a repeat ultrasound in 6 or 12 months by size and type |
| 3 | Low (1% to under 10%) | Ultrasound within 6 months if left in place; specialist ultrasound or MRI if solid; gynecologist |
| 4 | Intermediate (10% to under 50%) | Beyond screening: specialist ultrasound or MRI, gynecologist with a gynecologic oncologist |
| 5 | High (50% or more) | Beyond screening: gynecologic oncologist |
Source for the table: the O-RADS US v2022 assessment categories. (O-RADS US v2022)
Simple cysts by size
A simple cyst is a thin, smooth-walled sac of clear fluid with no solid parts. O-RADS scores it 2 when under 10 cm, or 1 when it is a normal follicle of 3 cm or less before menopause. (O-RADS US v2022)
| Size | Before menopause | After menopause |
|---|---|---|
| 3 cm or less | None (counted as a normal follicle) | None |
| Over 3 cm to 5 cm | None | Ultrasound in 12 months |
| Over 5 cm, under 10 cm | Ultrasound in 12 months | Ultrasound in 12 months |
| 10 cm or more | O-RADS 3: ultrasound within 6 months if left in place, and a gynecologist | |
Source for the table: the O-RADS US v2022 assessment categories. (O-RADS US v2022) O-RADS notes a shorter interval may be used for some people, for example because of clinical factors. (O-RADS US v2022)
Repeat checks and when they stop
- Smaller on the repeat scan (by 10% to 15% or more): no more scans. (O-RADS US v2022)(SRU 2019)
- Stable: O-RADS lists one more ultrasound at 24 months from the first scan; the SRU says a 2-year scan may help because measurements vary. (O-RADS US v2022)(SRU 2019)
- Larger (by 10% to 15% or more): O-RADS suggests ultrasound at 12 and 24 months from the first scan, then gynecology. The SRU says simple cysts that grow are likely cystadenomas, a benign growth. (O-RADS US v2022)(SRU 2019)
- New solid parts or other changes: the cyst is scored again with the full O-RADS terms. (O-RADS US v2022)(SRU 2019)
- Non-simple cysts: a smooth single cyst with internal echoes or incomplete septa, or a smooth two-part cyst, is still O-RADS 2. Over 3 cm and under 10 cm, O-RADS lists an ultrasound in 6 months. (O-RADS US v2022)
Typical benign findings
O-RADS lists set plans for lesions with a typical benign look: (O-RADS US v2022)
- Hemorrhagic cyst: before menopause, none up to 5 cm, and an ultrasound in 2 to 3 months for over 5 cm to under 10 cm. In the first 5 years after menopause, a scan in 2 to 3 months, a specialist ultrasound or MRI to confirm it.
- Dermoid cyst and endometrioma: a yearly ultrasound if left in place (for a dermoid of 3 cm or less, it may be considered); after menopause an endometrioma is confirmed first with a short-interval scan, specialist ultrasound or MRI.
- Paraovarian cyst, peritoneal inclusion cyst, hydrosalpinx: no imaging follow-up.
When MRI or a specialist is used
O-RADS says MRI with contrast is more specific than ultrasound for solid lesions and for cysts with solid parts. (O-RADS US v2022)(Strachowski 2023) RCOG says MRI should not be the first scan after menopause, but is the second-line test when ultrasound is inconclusive. (RCOG GTG 34) O-RADS refers scores 4 and 5 to a gynecologic oncologist, alone or with a gynecologist. (O-RADS US v2022)
CA-125 only in set cases
- After menopause: RCOG assesses a cyst with a CA-125 blood test and a transvaginal ultrasound. It counts a cyst as significant only if it is over 3 cm, and a simple single cyst of 3 cm or less needs no follow-up. It also says CA-125 should not be used on its own to decide whether a cyst is cancer. (RCOG GTG 34)
- Before menopause: RCOG says CA-125 is not needed when the scan clearly shows a simple cyst, and that it is often raised by fibroids, endometriosis, adenomyosis or pelvic infection. For a complex mass under age 40, it lists LDH, alpha-fetoprotein and hCG. (RCOG GTG 62)
- MedlinePlus says a CA-125 test may be done if an ultrasound is abnormal or after menopause. (MedlinePlus)
For what CA-125 can and cannot do as a screening test, see ovarian cancer screening.
MedlinePlus, when to contact a medical professional. Contact your provider if: (MedlinePlus)
- You have symptoms of an ovarian cyst
- You have severe pain
- You have bleeding that is not normal for you
Also contact your provider if you have had following on most days for at least 2 weeks:
- Getting full quickly when eating
- Losing your appetite
- Losing weight without trying
These symptoms may indicate ovarian cancer. Studies which encourage women to seek care for possible ovarian cancer symptoms have not shown any benefit. Unfortunately, there is no proven effective means of screening for ovarian cancer.
Routine age-based screening
A cyst found by chance does not replace the routine screenings for your age. For other findings on a scan, see kidney cyst found by chance, adrenal mass found by chance and lung nodule found by chance.
Where they differ:
- After menopause, 3 cm to 5 cm. O-RADS lists an ultrasound in 12 months. (O-RADS US v2022) The SRU recommends follow-up only above 3 to 5 cm, using 5 cm when the cyst is very well imaged. (SRU 2019) RCOG lists a repeat check in 4 to 6 months with a normal CA-125, and discharge after 1 year if the cyst is unchanged or smaller. (RCOG GTG 34)
- Before menopause, larger cysts. O-RADS lists one ultrasound at 12 months for over 5 cm to under 10 cm. (O-RADS US v2022) The SRU uses over 5 to 7 cm for follow-up. (SRU 2019) RCOG (2011) lists a yearly ultrasound for 5 to 7 cm and considers MRI or surgery above that. (RCOG GTG 62)
- CA-125. RCOG uses it with ultrasound to assess cysts after menopause. (RCOG GTG 34) The O-RADS tables do not use it; they base follow-up on the scan and menopause status. (O-RADS US v2022)
- How often to rescan. O-RADS notes there is little evidence for the best interval and length of follow-up. (O-RADS US v2022)
Your doctor decides what your result means for you.
Questions people ask
Is an ovarian cyst found by chance usually serious?
Usually not. ACOG says most adnexal masses are found by chance and most are benign. MedlinePlus says cancer is very unlikely with a simple cyst. (ACOG PB 174) (MedlinePlus)
Which simple cysts need no follow-up?
Before menopause, O-RADS lists no follow-up for a simple cyst up to 5 cm. After menopause, O-RADS and RCOG list none for a simple cyst of 3 cm or less. (O-RADS US v2022) (RCOG GTG 34)
When is the repeat ultrasound done?
O-RADS lists a repeat ultrasound in 12 months for larger simple cysts. If the cyst is smaller, no more scans; if stable, one more at 24 months. RCOG lists 4 to 6 months for a 3 to 5 cm cyst after menopause. (O-RADS US v2022) (RCOG GTG 34)
Do I need a CA-125 blood test?
Not always. RCOG measures CA-125 for cysts after menopause. Before menopause, RCOG says it is not needed when a scan clearly shows a simple cyst, and it is often raised for other reasons. (RCOG GTG 34) (RCOG GTG 62)
When is an MRI used?
When ultrasound cannot settle what a cyst is. O-RADS says MRI with contrast is more specific for solid lesions and cysts with solid parts; RCOG calls MRI the second-line test. (O-RADS US v2022) (RCOG GTG 34)
Related
- Fibroids seen by chance on a scan
- Thick womb lining found by chance after menopause
- Liver lesion found by chance: follow-up scans
- Gallbladder polyp found by chance: follow-up scans
- Pancreatic cyst found by chance: follow-up scans
- Ovarian cancer screening: CA-125 and ultrasound
- Kidney cyst found by chance: Bosniak follow-up
- Adrenal mass found by chance: follow-up tests
- Lung nodule found by chance: follow-up scans
- Pelvic exam: who needs one and what happens
- Screenings after menopause
- After an abnormal screening result
- False positives and overdiagnosis
- Screenings by age and gender