Ovarian torsion, also called adnexal torsion when the tube twists as well, is rotation of the ovary on its ligamentous pedicle. Venous and lymphatic drainage fail first, the ovary swells, and arterial inflow may be lost later. Ultrasound is the first-line study, yet it supports a clinical diagnosis rather than independently confirming or excluding torsion. At the scanner, document grayscale enlargement, ovarian position, a twisted pedicle when visible, comparison with the contralateral ovary, and Doppler findings without overreading preserved arterial flow.
Clinical Features and Risk Factors
Sudden unilateral pelvic or lower abdominal pain, often with nausea and vomiting, is the usual presentation. Pain can be intermittent if the ovary twists and untwists. Fever and laboratory changes are nonspecific and, when present, tend to be late. The same symptoms occur with cyst rupture, hemorrhagic cyst, appendicitis, and ureteral stone, so the examination should still address torsion.
Factors that raise concern include an adnexal mass, prior ipsilateral torsion, pregnancy (especially with a corpus luteum), ovarian hyperstimulation, and the more mobile adnexa of childhood, where a mass is not required. A simple ovarian cyst is a frequent lead point in reproductive-age patients. Chronically enlarged ovaries, including those in polycystic ovarian syndrome, can be more mobile, although torsion remains uncommon relative to how often those ovaries are scanned.
Grayscale Findings of Ovarian Torsion
Unilateral ovarian enlargement relative to the opposite ovary is the most consistent grayscale feature. Edematous stroma may look hyperechoic or heterogeneous, with follicles displaced peripherally. Free fluid is common and nonspecific. Report any underlying mass, including size and internal features, because it explains risk and affects surgical planning.
Also look for:
- Abnormal ovarian location, including midline, far lateral, or cranial position
- A thickened, edematous fallopian tube
- A round or concentric extraovarian structure from the twisted pedicle
- Direct tenderness over the ovary, noted as a clinical observation
Technique and Contralateral Comparison
Scan both adnexa with matched transducer, depth, and gain. Measure three dimensions and, when a mass is present, separate residual ovary from the mass if possible. Start transabdominal when pain is severe, the mass is large, or transvaginal imaging is not appropriate. Add transvaginal views when they can be obtained safely. They usually show the pedicle and waveforms more clearly. Peripheral follicles in an edematous ovary can mimic a crowded antral follicle pattern. Laterality, stromal edema, pain, and the pedicle distinguish acute torsion from a chronically large ovary.
Doppler Evaluation, Whirlpool Sign, and Pitfalls
Color and spectral Doppler complement grayscale. They do not replace it. Venous flow is typically lost before arterial flow. Absent venous signals with residual arterial flow should increase suspicion, not reassure.
The whirlpool sign is the most specific ultrasound feature when seen. The twisted pedicle appears as a spiral or target of coiled vessels on grayscale or color Doppler. Sweep the pedicle in two planes and use a low pulse repetition frequency. Spectral sampling helps confirm that the vessels are ovarian rather than iliac.
Document venous flow, arterial resistance or absent diastolic flow, side-to-side comparison with identical settings, and any color whirlpool. Always optimize Doppler on the asymptomatic ovary first. Symmetric absence of flow is more often technical than bilateral torsion, which is uncommon.
Preserved arterial flow does not exclude ovarian torsion. Dual supply from the ovarian and uterine arteries, incomplete twist, and intermittent detorsion can leave arterial signals in an ischemic ovary. Other traps include a nearly normal appearance between intermittent episodes, a large cyst hiding the pedicle, and gain or scale settings that create a false impression of no flow. A painful, enlarged, displaced ovary still warrants surgical concern even if arterial waveforms are present.
Findings Checklist for Timely Referral
- Unilateral enlargement and stromal heterogeneity versus the contralateral ovary
- Ovarian position and any lead-point mass
- Whirlpool sign or twisted pedicle: present, absent, or not seen
- Venous and arterial Doppler on both sides, with settings noted
- Free fluid and any hemorrhagic features
- A statement that detectable flow does not exclude torsion
Red flags for urgent surgical consultation include an acutely painful enlarged ovary, a visible whirlpool, absent venous flow, and a matching clinical history. Treatment is operative detorsion, with ovarian conservation whenever tissue may still be viable. Imaging cannot prove viability well enough to delay the operating room. This review supports clinical judgment and current guidelines. It is not advice about an individual patient.
Compare both ovaries, search for the pedicle, and state residual uncertainty clearly so referral is not delayed. IAME offers accredited ultrasound CME courses on pelvic and ovarian imaging for clinicians who want structured review of technique and interpretation.
Frequently Asked Questions
What are the risk factors for ovarian torsion?
The dominant risk factor is an enlarged ovary or adnexal mass that acts as a lead point, most often a cyst. Prior torsion, pregnancy, ovarian hyperstimulation, and the mobile adnexa of childhood also increase risk. Torsion can still occur in a normal-sized ovary, so risk factors change pretest probability rather than make or exclude the diagnosis.
How is ovarian torsion diagnosed on ultrasound?
Begin with grayscale comparison of size, echotexture, and position, then search for a twisted vascular pedicle. Add color and spectral Doppler of both ovaries, looking for venous compromise and the whirlpool sign. High clinical suspicion still leads to laparoscopy, which remains the reference standard.
Does Doppler flow rule out ovarian torsion?
No. Arterial flow may persist because of dual blood supply, partial torsion, or intermittent twisting. Absent flow increases confidence, but present flow does not exclude ischemia. An enlarged, tender, malpositioned ovary with acute pain still needs surgical evaluation.
What is the treatment for ovarian torsion?
Prompt surgical detorsion, usually laparoscopic, with conservation of the ovary when possible. Ultrasound does not determine viability with enough certainty to postpone surgery. Any coexisting mass is managed according to operative findings and specialty guidelines.
