Ovarian Cyst on a Scan: When It’s Harmless vs When You Need an Oncologist

“You have an ovarian cyst” is one of the most common results an Indian woman hears at the end of a routine pelvic ultrasound. The reactions vary from complete unconcern to outright panic, and both are usually wrong. Most ovarian cysts are entirely benign and will resolve on their own. A small fraction need surgery. An even smaller fraction need cancer-specialist evaluation.

This article maps the features that distinguish the three categories, so you can have a more useful conversation with your doctor about which one applies to you.

What a cyst actually is

An ovarian cyst is any fluid-filled sac on or within the ovary. They occur for many reasons, most of them entirely physiological:

• Functional cysts, the most common type. The ovary makes cysts every month as part of normal ovulation. Most resolve in 1–3 cycles.
• Endometriotic cysts (chocolate cysts), caused by endometriosis. Filled with old blood.
• Dermoid cysts (teratomas), benign tumours containing skin, hair, occasionally cartilage or teeth. Mostly seen in younger women.
• Serous and mucinous cystadenomas, benign tumours of the ovarian surface or interior. Can grow large but are not cancerous.
• Borderline ovarian tumours, a category between benign and frankly cancerous. Behave indolently in most cases.
• Malignant ovarian tumours, frank ovarian cancer. Multiple histological types with different behaviour and treatment.

The point of the work-up is to figure out which category a specific cyst falls into.

The features that matter on imaging

When a radiologist describes an ovarian cyst, they’re looking at several features. The features that suggest benign behaviour:

• Small size (under 5 cm)
• Simple appearance (thin walls, clear fluid, no internal structures)
• Round shape, regular outline
• No solid component
• No internal blood flow on Doppler
• Both ovaries appear normal
• No free fluid in the pelvis

Features that raise concern for malignancy:

• Larger size (especially over 10 cm)
• Complex appearance, thick walls, septations (internal walls dividing the cyst), solid components
• Irregular outline
• Internal blood flow on Doppler imaging
• Bilateral cysts (both ovaries involved)
• Free fluid in the pelvis or abdomen (ascites)
• Other findings, enlarged lymph nodes, peritoneal nodules

The IOTA criteria and the O-RADS classification system are formal scoring systems clinicians use to combine these features into a risk category. Most modern ultrasound reports in India now include an O-RADS score (1 to 5, with higher numbers indicating higher concern).

When CA-125 helps and when it doesn’t

CA-125 is a blood tumour marker that’s elevated in many, but not all, ovarian cancers. It is most useful:

• In postmenopausal women with an ovarian cyst (high specificity for cancer if elevated)
• In monitoring known ovarian cancer during and after treatment

It is less useful in:

• Premenopausal women, because many benign conditions (endometriosis, fibroids, pelvic inflammation, even menstruation itself) elevate CA-125
• As a screening test in the general population (false-positive rate is too high)

For a premenopausal woman with a cyst, a modestly elevated CA-125 is rarely diagnostic on its own. The imaging features matter more.

When to repeat the scan vs when to escalate

For a typical premenopausal woman with a simple-looking cyst under 5 cm, the standard recommendation is a repeat ultrasound in 6–12 weeks. Most functional cysts resolve in that window. If the cyst persists or grows, further evaluation is needed.

For a postmenopausal woman, the threshold is lower: – Any complex cyst, refer for specialist evaluation – Even a simple cyst over 5 cm, usually warrants MRI and CA-125 – Persistent simple cyst over 3 cm, usually warrants follow-up imaging

For women of any age, immediate specialist referral is appropriate when: – The O-RADS score is 4 or 5 – The cyst is large (over 10 cm) regardless of appearance – There’s free fluid, peritoneal nodularity, or enlarged lymph nodes – The cyst has solid components, septations, or blood flow within solid areas – There is a strong family history of ovarian or breast cancer

What happens if surgery is recommended

If a cyst is recommended for surgical removal, two technical questions matter:

1. Who’s doing the surgery? Cysts with any concerning features should be removed by a gynaecological oncosurgeon, not a general gynaecologist. This is because the surgical approach is different, the cyst must be removed intact (without spillage), staging may be required if it turns out to be cancer, and the operating team needs to be prepared to convert to a complete cancer-staging operation if frozen-section pathology shows malignancy.
2. What’s the approach? For low-concern cysts in premenopausal women, laparoscopic removal with cystectomy (cyst removed, ovary preserved) is standard. For higher-concern cysts, an open or robotic approach with the ability to expand the operation if cancer is found is appropriate.

This is the critical distinction: a cyst that turns out to be cancer requires a complete cancer-staging operation, and that operation is materially compromised if a general surgeon has already spilled the contents during initial removal. Getting the right surgeon for the first operation matters.

What to ask your gynaecologist

A few specific questions that produce useful answers:

1. What is the O-RADS score or risk category for my cyst?
2. What is the CA-125 result, and how should it be interpreted given my age and other conditions?
3. Should an MRI be added to refine the diagnosis?
4. If surgery is recommended, who will perform it, and are they trained in gynaecological oncology in case the cyst turns out to be cancer?
5. What are the chances of needing a more extensive operation if intraoperative frozen-section pathology shows cancer?

When you need an oncologist

A formal ovarian cyst specialist evaluation by a gynaecological oncosurgeon is appropriate when:

• O-RADS 4 or 5 features on imaging
• Elevated CA-125 in a postmenopausal woman
• Large cyst (>10 cm) regardless of features
• Strong family history of gynaecological cancer
• Any cyst with associated ascites, peritoneal disease, or pleural effusion
• A previous cyst that has grown or developed concerning features on follow-up

In these situations, the operation needs to be planned as a potential cancer operation from the start, not as a benign cystectomy that might “convert” to cancer surgery mid-procedure.

The bottom line

Most ovarian cysts are benign and will resolve on their own. A small fraction need surgery, and an even smaller fraction need cancer-specialist evaluation. The features that distinguish the three categories, size, complexity, internal structure, blood flow, CA-125, family history, are reliable and well-defined.

The clinical mistake to avoid is two-fold: dismissing a cyst with concerning features as “probably benign,” or panicking about a simple cyst that almost certainly is benign. The right approach is structured: get the imaging characterisation right, get the right blood tests, and escalate to the right specialist when the features warrant it.

About the author

This article was reviewed by Dr. Nishtha Tripathi Patel (MBBS, DGO, DNB, Fellowship in Gynaecological Oncology, ESGO-certified), an ESGO-certified gynaecological oncosurgeon in Ahmedabad specialising in surgical evaluation and treatment of complex ovarian masses. Reach her practice at +91 76988 00333.