Ovarian cysts: which ones need surgery, and which ones do not

Few lines on a report worry a woman more than “ovarian cyst”. The first thing worth saying is usually the most reassuring: the ovary makes a cyst every single month. A follicle grows, releases an egg and collapses. Catch that on a scan at the wrong moment and it is reported, accurately, as a cyst.

So the question is almost never whether there is a cyst. It is which kind, and whether it needs anything done to it. Most do not.

How often a cyst turns out to be cancer

The Royal College of Obstetricians and Gynaecologists puts the risk of a symptomatic ovarian cyst in a woman before menopause being malignant at roughly 1 in 1,000, rising to about 3 in 1,000 by the age of 50. After menopause the arithmetic shifts, which is why the follow-up rules below are stricter for an older woman with exactly the same scan picture. That is why the aim of assessment is not to remove cysts, but to pick out the few that need removing.

The kinds of cyst, and why type matters more than size

A 4 cm dermoid and a 4 cm follicular cyst are the same size and nothing like the same problem. That is the most useful thing to understand about a cyst report.

What actually decides surgery

Three questions, taken together. Size matters mostly because it changes what the first two mean.

Does it look simple?

A simple cyst is one thin-walled compartment of clear fluid with no solid area inside it, no finger-like projections into the cavity, no blood flow through solid tissue and no free fluid in the pelvis. Solid parts, several papillary projections, a large irregular multi-compartment mass, strong blood flow or ascites move it out of that category.

There is a published checklist of these features. Validated in 1,983 women across eight countries, it picked up malignancy with a sensitivity of 95% and a specificity of 91% — better than any blood test. One caveat keeps everyone honest: up to a fifth of borderline tumours can look like a plain simple cyst, so a reassuring appearance is a reason to watch, not to stop watching.

Has it persisted?

A functional cyst has a short life. The RCOG guideline notes that a simple cyst under 50 mm before menopause is almost always gone within three menstrual cycles and needs no follow-up at all. One still the same size after two or three cycles was probably never functional, and that is where the conversation changes. Worth knowing, since the contraceptive pill is often prescribed in the belief that it helps: it does not make a functional cyst resolve any faster.

Is it causing trouble?

Persistent pelvic pain, pressure on the bladder or bowel, pain during intercourse, a cyst large enough to be felt, or — after menopause — new bloating, early fullness after meals, weight loss or bleeding. Symptoms shift the balance towards surgery whatever the scan shows.

Where blood tests help, and where they mislead

CA-125 is useful in the right place and misleading everywhere else. The RCOG guidance is explicit that it is not needed when the scan has clearly diagnosed a simple cyst, and that it is unreliable before menopause because endometriosis and fibroids push it up — in advanced endometriosis it can run into the hundreds or thousands with no cancer anywhere. It fails the other way too: it is raised in only about half of early-stage epithelial ovarian cancers, so a normal result does not clear a suspicious scan.

Where it earns its place is inside the Risk of Malignancy Index, which multiplies an ultrasound score by menopausal status by the CA-125 level. At the usual cut-off of 200 the pooled figures are a sensitivity of 78% (95% CI 71 to 85) and a specificity of 87% (95% CI 83 to 91) — enough to decide who should be seen by a gynaecological cancer team, not enough to be used alone. Under 40 with a complex mass, LDH, alpha-fetoprotein and hCG are added, germ-cell tumours being the ones that occur at that age.

Polycystic ovaries are not cysts waiting for surgery

This confusion causes real distress, so it is worth stating plainly. The 2023 international PCOS guideline defines the polycystic appearance as 20 or more follicles in at least one ovary. Those are follicles — the ovary’s normal monthly candidates, in larger numbers — not cysts, and no operation treats the appearance. PCOS is managed through cycles, weight, insulin resistance and, where pregnancy is the goal, ovulation induction. Laparoscopic ovarian surgery has one narrow role in that guideline: second line for anovulatory infertility that has not responded to tablets.

The pain that should not wait

A cyst can twist the ovary on its own blood supply. Torsion is the one ovarian emergency, and the ovary is lost or saved on the clock.

A five-year review of 81 surgically confirmed torsions at a tertiary centre in southern India is the most useful published series here. The median age was 26, and a pre-existing ovarian mass was present in 88.8% of cases — mostly substantial ones, 62.5% at 6 to 10 cm and 29.2% over 10 cm, with only 8.3% at 5 cm or less. The median time from first pain to reaching hospital was 24 hours, with a further 12 hours before surgery. The ovary could be conserved in 43.2% of cases and had to be removed in 56.8%. No cancer was found in the series — this is a problem of blood supply, not of malignancy.

So for any woman known to have a cyst: sudden, severe, one-sided pelvic pain, usually with nausea or vomiting, is a same-hour problem, not a wait-for-the-morning one.

If a cyst does need removing

For a cyst that looks benign, keyhole surgery is the standard route; the RCOG guideline prefers it to open surgery in suitable patients, earlier discharge being one reason. A few points patients usually want to know:

• The cyst, not the ovary. In a woman of reproductive age the aim is cystectomy with the ovary preserved. Removing an ovary is a decision taken for a reason, not a default.
• Spill is managed, not ignored. A retrieval bag is used where appropriate. Chemical peritonitis after spillage from a dermoid occurs in under 0.2% of cases.
• Draining a cyst is not treating it. Recurrence after laparoscopic aspiration runs at 53% to 84%; for an endometrioma, aspiration alone can recur in close to 100% of cases.
• Everything goes to histopathology. Whatever the scan suggested, the specimen is reported by a pathologist.
• Robot-assisted surgery. Where a robotic approach is appropriate, Dr. Rahul Khatri operates at Apollo Hospital, Gandhinagar, where he is attached. There is no surgical robot at Cosmic.

Cysts, surgery and fertility

This is where the decision needs real care, because cyst surgery is not free of cost to the ovary. For an endometrioma, current European guidance prefers cystectomy over draining and coagulating the cyst, particularly above 3 cm. But a published meta-analysis found median AMH — the usual marker of ovarian reserve — falling from 3.1 to 1.51 ng/mL in the first months after cystectomy, usually recovering by a year, with a lasting reduction mainly where both ovaries were operated. Premature ovarian insufficiency after bilateral excision is put at 2.4%.

There is also no evidence that removing an endometrioma first improves IVF results. Where IVF is already indicated, surgery beforehand is done for pain or for access to the ovaries, not to raise the success rate. For a woman who still wants to conceive, then, the discussion before cyst surgery is as much about ovarian reserve as about the cyst.