Pelvic ultrasound in gynaecology: cysts, fibroids, torsion
- Finding
A pelvic scan shows the uterus and ovaries, telling harmless cysts and fibroids apart from torsion and lumps that need a specialist.
What it is
Pelvic ultrasound is the first imaging test in gynaecology. A transabdominal view with a full bladder gives the overview and shows large masses; the transvaginal view gives the detail of the endometrium, myometrium and ovaries. Colour Doppler adds blood flow. Most findings are benign and can be named by their pattern: a simple functional cyst, a haemorrhagic cyst, an endometrioma, a dermoid, or a fibroid. The scan also looks for the urgent pictures, such as an enlarged ovary in torsion or a tubo-ovarian abscess, and for the features that make an adnexal mass suspicious for cancer. MRI is the problem-solving test when ultrasound cannot say what a mass is.
What it looks like
- Simple cyst: round, anechoic, thin smooth wall, bright posterior enhancement, no solid part and no internal flow; in a premenopausal woman it is usually a follicle or functional cyst.
- Haemorrhagic cyst: fine lacy or net-like internal echoes or a retracting clot that has no flow on Doppler; it usually resolves within weeks.
- Endometrioma: a thick-walled cyst full of uniform low-level «ground-glass» echoes.
- Dermoid (mature cystic teratoma): a bright echogenic nodule or plug, fine bright lines and dots from hair, sometimes a fat–fluid level and shadowing that hides the back of the mass.
- Fibroid (leiomyoma): a well-defined, rounded, usually hypoechoic myometrial mass with a whorled texture, edge shadows and flow around its rim.
- Ovarian torsion: an enlarged, oedematous ovary with follicles pushed to the periphery, often a mass as the lead point, free fluid, and a twisted pedicle («whirlpool sign»).
- Suspicious adnexal mass: solid parts with internal flow, thick or irregular septa, papillary projections, ascites or peritoneal nodules.
Why it looks that way
- Fluid is anechoic and transmits sound well, so simple cysts are black with a bright band behind them; blood and debris add echoes.
- Fibroids are dense bundles of smooth muscle and fibrous tissue that attenuate sound, which gives the edge shadows and fan-like («venetian blind») shadowing.
- In torsion, twisting first blocks the low-pressure veins and lymphatics, so the ovary swells before arterial flow stops; this is why Doppler flow can still be seen.
- The ovary has a dual blood supply (ovarian artery and a branch of the uterine artery), another reason flow may persist despite torsion.
Differential and pitfalls
- Normal Doppler flow does not exclude ovarian torsion: the diagnosis is clinical plus an enlarged ovary, and suspicion means surgery.
- A torsed ovary is usually larger than the other one; a normal-sized ovary with normal flow makes torsion much less likely.
- In a woman of reproductive age with pelvic pain, do a pregnancy test first: ectopic pregnancy is in the same differential.
- Locate fibroids by their relation to the cavity (submucosal, intramural, subserosal, pedunculated): submucosal ones cause bleeding and infertility.
- Adenomyosis looks different from fibroids: a globular uterus with asymmetric, poorly defined myometrial thickening and small myometrial cysts, without a separate mass.
- Postmenopausal bleeding: a thin endometrium (about 4 mm or less) makes cancer unlikely; a thicker or irregular one needs sampling.
- A simple cyst in a postmenopausal woman is usually benign but follows a guideline-based follow-up; any solid part changes the picture.
Next step
- Suspected torsion (sudden pain, vomiting, enlarged ovary): call gynaecology for laparoscopy now; do not wait for a further scan.
- Haemorrhagic or functional-appearing cyst: repeat scan in about 6 to 12 weeks, ideally after a period, to confirm resolution.
- Adnexal mass with suspicious features or ascites: refer to gynaecologic oncology; MRI if ultrasound is indeterminate.
- Fever, pelvic pain and a complex adnexal collection: treat as tubo-ovarian abscess and involve gynaecology for antibiotics or drainage.
- Postmenopausal bleeding with a thickened endometrium: refer for endometrial sampling.
Test yourself
Think of the answer, then tap the question to see it.
Why can colour Doppler show blood flow in an ovary that is torsed?
Twisting blocks the veins first, and the ovary has a dual arterial supply, so arterial flow can persist; flow does not exclude torsion.
What does a dermoid cyst typically look like on pelvic ultrasound?
A cyst with a bright echogenic plug, fine bright lines and dots from hair, sometimes a fat–fluid level, and shadowing that hides its back wall.
Which adnexal ultrasound features raise concern for malignancy?
Solid components with internal flow, thick or irregular septa, papillary projections, ascites and peritoneal nodules.
How is a haemorrhagic cyst told apart from a solid ovarian mass?
Its internal lacy echoes or retracting clot have no flow on colour Doppler, and it shrinks or resolves on a repeat scan weeks later.
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Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.
Sources: Transvaginal Ultrasonography (StatPearls (NCBI Bookshelf), 2022); Ovarian Cyst (StatPearls (NCBI Bookshelf), 2023); Ovarian Torsion (StatPearls (NCBI Bookshelf), 2023); Uterine Leiomyomata (StatPearls (NCBI Bookshelf), 2025).
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