Ovarian cyst

What it is

An ovarian cyst is a fluid-filled sac that forms on or inside one of the ovaries, affecting an estimated 10 out of 100 women at some point in their lives. Also called an adnexal cyst or ovarian follicular cyst depending on its origin, the condition is overwhelmingly benign: the vast majority of cysts resolve spontaneously within one to three menstrual cycles without any treatment. Ovarian cysts are most common during the reproductive years but can develop at any age, including in newborns and postmenopausal women.

Canadian patients should know that most cysts are found incidentally on pelvic ultrasound — a test widely available through LifeLabs and Dynacare requisitions — ordered for an unrelated reason. The finding rarely signals cancer, particularly in premenopausal women with simple, thin-walled cysts. It is also important to distinguish an individual ovarian cyst from polycystic ovary morphology seen in PCOS (polycystic ovary syndrome), which is a separate hormonal condition requiring a different diagnostic workup and management pathway.

Causes and mechanism

The most common type is the functional cyst, which arises directly from the hormonal events of ovulation:

Type	Mechanism	Typical course
Follicular cyst	Follicle grows but does not release its egg or reabsorb	Resolves in 1–3 cycles
Corpus luteum cyst	Post-ovulation corpus luteum fills with fluid or blood instead of breaking down	Usually resolves; rupture can cause sharp pain
Endometrioma ("chocolate cyst")	Endometrial tissue bleeds into a cyst on the ovary; associated with endometriosis	Persists; can reduce ovarian reserve over time
Dermoid cyst (mature teratoma)	Derived from egg cells; contains hair, skin, or sebaceous material	Almost always benign; grows slowly; torsion risk
Cystadenoma	Arises from ovarian surface epithelium; serous or mucinous fluid	Can grow large; surgical removal often needed
Paraovarian cyst	Arises from tissue adjacent to the ovary, not the ovary itself	Variable; often managed conservatively

Hormonal factors that disrupt ovulation — including PCOS and fertility medications that stimulate multiple follicle development — increase the likelihood of functional cyst formation. Ovarian hyperstimulation syndrome, a complication of assisted reproduction, can produce multiple follicular cysts simultaneously.

Symptoms and diagnosis

Most ovarian cysts cause no symptoms and are discovered incidentally. When symptoms do occur, they typically include a dull ache or pressure in the lower abdomen on the affected side, bloating, pain during intercourse (dyspareunia), or irregular menstrual periods.

Two complications require urgent attention:

• Rupture: sudden, sharp pelvic pain, often with nausea and vomiting. Most ruptured cysts resolve without intervention, but haemorrhagic rupture may require surgery.
• Ovarian torsion: the ovary twists around its supporting ligaments, cutting off blood supply. This is a surgical emergency presenting as severe, sudden pelvic pain, frequently with nausea and vomiting.

Diagnosis typically follows this sequence:

1. Pelvic ultrasound — the primary investigation; assesses cyst size, structure (simple vs. complex), echogenicity, and blood flow.
2. CA-125 blood test — considered when malignancy is a concern, though it is non-specific and elevated in many benign conditions including endometriosis and fibroids.
3. Hormone panel (FSH, LH, estradiol, androgens) — ordered if a hormonal cause or PCOS is suspected.
4. MRI — used to further characterize complex or diagnostically uncertain cysts.

Treatment options

Management depends on cyst type, size, symptoms, and malignancy risk.

Watchful waiting is the first approach for most simple functional cysts in women of reproductive age. A repeat ultrasound at 6 to 12 weeks confirms resolution in the majority of cases.

Medical management includes NSAIDs for symptomatic pelvic discomfort. Hormonal contraceptives do not dissolve existing cysts but may prevent new functional cysts by suppressing ovulation.

Surgical management:

• Laparoscopic cystectomy — keyhole removal of the cyst while preserving the ovary; preferred for persistent, large, symptomatic, or complex cysts.
• Oophorectomy — removal of the entire ovary; reserved for cases where cystectomy is not feasible or malignancy cannot be excluded.

For endometriomas: surgical excision is generally recommended for cysts above 4 cm, particularly before IVF, as endometriomas can impair egg retrieval and reduce ovarian reserve. Hormonal suppression with GnRH analogues, progestogens, or combined oral contraceptives may reduce size and recurrence.

For dermoid cysts: surgical removal is generally recommended regardless of symptoms, given the risk of torsion and progressive growth over time.

When to see a clinician in Canada

Go to the nearest emergency department immediately if you develop sudden, severe pelvic pain — especially with nausea, vomiting, or fever — as this may indicate ovarian torsion or a haemorrhagic ruptured cyst, both of which are surgical emergencies.

Book an appointment with your family physician or a gynaecologist if you have persistent or recurrent pelvic pain or pressure, unexplained bloating, pain during intercourse, irregular periods, or if you have been told you have an ovarian cyst and have not had a follow-up ultrasound to confirm resolution. Referral to a gynaecologist is available through the provincial health system in all provinces; wait times vary, but urgent referrals for complex or symptomatic cysts are typically triaged within weeks. Canadian telehealth platforms such as Maple or Felix can facilitate initial assessment and requisition of pelvic ultrasound while you await a specialist appointment.

Limitations and open questions

Research is still emerging on the long-term impact of endometriomas on ovarian reserve and the optimal timing of surgical intervention before fertility treatment. The CA-125 test is widely used but poorly specific: Health Canada has not issued a formal screening protocol for ovarian cysts using this marker, and its role remains limited to risk stratification rather than diagnosis. Evidence on whether hormonal suppression after endometrioma surgery meaningfully reduces recurrence rates is mixed, with some Cochrane reviews showing modest benefit and others showing no significant difference in long-term outcomes. The threshold for surgical referral in postmenopausal women with simple cysts continues to be debated in the literature, with some guidelines favouring conservative monitoring for cysts under 1 cm with normal CA-125, while others recommend earlier intervention. Guidance from the Society of Obstetricians and Gynaecologists of Canada (SOGC) on adnexal mass management is an important reference point for Canadian clinicians, though individual provincial protocols may vary.