Ovarian Torsion on Ultrasound: What to Look For and When to Call It

Ovarian torsion is a surgical emergency — the ovary twists on its pedicle, compromising blood supply and leading to irreversible ischemia if not treated promptly. Ultrasound is the primary imaging tool, but the diagnosis is clinical as much as sonographic. Understanding the findings — and their limitations — is essential.

Clinical Presentation

• Sudden onset severe unilateral pelvic pain, often colicky
• May radiate to the flank or lower back
• Nausea and vomiting (common, sometimes the predominant symptom)
• Can present in any age group — peak in reproductive years, but occurs in children and postmenopausal women
• Prior history of ovarian cyst or mass (risk factor — provides a pivot point for torsion)
• Pain may wax and wane (intermittent torsion with spontaneous detorsion)

Ultrasound Findings

Primary Findings

Enlarged ovary: The most consistent finding in ovarian torsion. A torsed ovary is typically > 4 cm (often much larger — 6–10 cm). Compare carefully to the contralateral side.

Normal ovary volume: length × width × height × 0.523. Normal < 20 mL in reproductive age, < 8 mL postmenopausal.

Peripheral follicles: The classic appearance — multiple small follicles displaced to the periphery of an edematous, echogenic stroma. This "string of pearls" or peripheral follicle arrangement occurs because the edematous stroma expands outward while the follicles are compressed to the periphery.

Edematous, echogenic stroma: The ovarian stroma becomes diffusely echogenic and enlarged due to vascular congestion and edema. The ovary looks "filled in" and heterogeneous.

Associated mass: In the majority of cases (70–80%), there is an underlying ovarian mass or cyst providing the pivot point for torsion. Dermoid, functional cyst, and benign ovarian neoplasm are the most common.

Whirlpool Sign

The whirlpool sign is the most specific finding for ovarian torsion and represents the twisted pedicle (the ovarian ligament, blood vessels, and fallopian tube twisted on themselves).

How to find it:

• Use color Doppler and look adjacent to the torsed ovary
• A twisted, coiled vascular structure with swirling color Doppler signal
• Rotate the probe to follow the twisted pedicle
• The twist may be visible on B-mode as a target-like or coiled soft tissue structure

When you see the whirlpool sign, the diagnosis is made. Its sensitivity is ~75% but specificity approaches 100%.

Doppler Flow Findings

This is the most misunderstood aspect of ovarian torsion:

Absent ovarian blood flow on Doppler: Highly specific when present — if you see no flow in an enlarged, edematous ovary, torsion is the diagnosis.

HOWEVER — normal or even increased Doppler flow does NOT rule out torsion.

This is the critical teaching point. Blood flow may be present in:

• Intermittent/partial torsion (the ovary twists and partially untwists)
• Early torsion (venous obstruction occurs before arterial)
• A torsed ovary with adequate collateral supply

Studies show that Doppler flow is present in 40–60% of surgically confirmed torsion cases.

If the ovary is enlarged and the clinical picture fits — do not reassure the patient or the clinician based on normal Doppler flow alone.

Free Fluid

Free fluid in the pelvis or cul-de-sac is common in torsion — may represent a ruptured cyst (the predisposing lesion) or peritoneal reaction to the ischemic ovary.

Complex fluid (heterogeneous, echogenic) is more concerning than simple free fluid.

What a Normal Ovary Looks Like

Before calling something abnormal:

• Size: 3 × 2 × 2 cm (volume ~7 mL) — varies by cycle phase
• Echogenicity: Homogeneous intermediate echogenicity with visible follicles
• Clear Doppler signal: Central stromal flow + peripheral color signal

An asymmetric ovary with a contralateral side measuring 2× the other should always raise concern.

Pediatric Torsion

Ovarian torsion in children has important differences:

• Normal (non-pathologic) ovaries can torse in girls — the ovary's mobility relative to pelvic structures is greater
• Peak age: neonates and early adolescence
• A neonatal ovarian cyst found prenatally can torse in utero or post-delivery
• Always consider torsion in a girl with acute lower abdominal or pelvic pain — regardless of age

Reporting Language

Be decisive — don't hedge if the findings are present.

Positive findings:

• "Right ovary markedly enlarged measuring 8.2 × 5.4 × 5.0 cm (volume 118 mL) with a heterogeneous echogenic stroma and peripheral displacement of follicles. Whirlpool sign identified adjacent to the right ovary. No identifiable Doppler flow within the right ovarian parenchyma. Findings are highly suspicious for right ovarian torsion. Urgent clinical correlation recommended."

Normal Doppler but suspicious morphology:

• "Left ovary enlarged at 5.8 × 4.2 × 3.9 cm with edematous stroma and peripheral follicles. Doppler flow is present, however the morphologic findings are concerning for possible ovarian torsion. Normal Doppler does not exclude torsion. Urgent gynecologic evaluation is recommended given clinical presentation."

Whirlpool sign present:

• "Whirlpool sign identified — twisted ovarian pedicle visible adjacent to the right ovary on color Doppler. Combined with ovarian enlargement and absent parenchymal Doppler flow, findings are consistent with ovarian torsion."

What to Tell the Radiologist

If you see an enlarged, edematous ovary with peripheral follicles in a patient with acute pelvic pain — flag the study immediately. This is a time-sensitive diagnosis. Don't wait for the routine read queue.

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SonoBuddy's Pathologies section includes ovarian torsion findings, red flags, and differentials. Gynecologic measurements are in the Measurements section.