KEY FACTS
Terminology
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Adnexal torsion is more accurate term than ovarian torsion, as torsion usually also includes fallopian tube
Imaging
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Ovary > 4 cm long or > 20 cm³ in volume
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Enlarged, heterogeneously echogenic ovarian stroma
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Multiple small, fluid-filled follicles displaced peripherally due to edematous stroma &/or mass
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May see follicular ring sign: Thin echogenic rim around follicles in early torsion
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Whirlpool sign: Coiled, twisted pedicle
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Flow pattern depends on degree of vascular obstruction and chronicity of torsion
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Venous flow affected 1st
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Due to dual arterial blood supply to ovary, arterial flow may be preserved
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CT
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Twisted pedicle most specific sign but seen in < 1/3 of cases (use multiplanar reformations)
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Heterogeneous, minimal, or absent enhancement indicates evolution from ischemia to infarction
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Top Differential Diagnoses
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Hemorrhagic corpus luteum
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Pelvic inflammatory disease
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Ectopic pregnancy
Pathology
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In adults, 50-90% have associated ovarian mass that serves as lead point
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Large physiologic follicular cyst or corpus luteum cyst most common, followed by dermoid
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Presence of venous flow suggests viable ovary
Scanning Tips
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Compare with asymptomatic contralateral side
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Presence of normal blood flow does not exclude torsion
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Always look for underlying mass, which can act as lead point for torsion
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Ovaries are highly mobile and when torsed, may be located in unusual locations
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When ovaries are deep in location, it may be difficult to detect color Doppler flow even in normal ovaries
containing a hemorrhagic cyst with multiple peripheral follicles 
. One of the follicles demonstrates the follicular ring sign 
.
with no color Doppler signal. Alternating red and blue color signal 
represents a twisted vascular pedicle, which is best seen during real time.
.
in the left adnexal mass with associated hemoperitoneum 
(note the uterus 
).
and large, bluish hemorrhagic cyst 
.
. Blood flow is seen 
, and despite normal Doppler waveforms (not shown), torsion was suspected and confirmed at surgery.
