Ovarian torsion, also sometimes termed adnexal torsion or tubo-ovarian torsion, refers to rotation of the ovary and portion of the fallopian tube on the supplying vascular pedicle.
It can be intermittent or sustained and results in venous, arterial and lymphatic stasis. It is a gynecological emergency and requires urgent surgical intervention to prevent ovarian necrosis.
Ovarian torsion has a bimodal age distribution occurring mainly in young women (15-30 years) and post-menopausal women. Approximately 20% of the cases occur during pregnancy 1.
Torsion occurs due to two main reasons 2:
- hypermobility of the ovary: <50%
- adnexal mass: ~50-80%
Most patients present with severe non-specific lower abdominal and pelvic pain, either intermittent or sustained, nausea, and vomiting. There is adnexal tenderness. A raised white cell count is common.
The result of vascular compromise secondary to ovarian torsion is hemorrhagic infarction and necrosis, that can occur as rapidly as within hours of torsion onset.
In adulthood, causes include both benign and malignant ovarian tumors, polycystic ovaries and adhesions. In early pregnancy, a torsion can occur secondary to a corpus luteal cyst or laxity of the adjacent tissues.
The main feature of torsion is ovarian enlargement due to venous/lymphatic engorgement, edema and hemorrhage. Secondary signs include free pelvic fluid, an underlying ovarian lesion, reduced or absent vascularity and a twisted dilated tubular structure corresponding to the vascular pedicle. Adnexal torsion is commonly unilateral, with a slight (3:2) right-sided predilection (presumably due to the protective effects of the sigmoid colon on the left) 6,8.
Ultrasound is the initial imaging modality of choice. Sonographic features include:
- enlarged hypo- or hyperechoic ovary
- peripherally displaced follicles with hyperechoic central stroma
- midline ovary
- free pelvic fluid: may be seen in >80% of cases
- an underlying ovarian lesion may be seen (possible lead point for torsion)
- a long-standing infarcted ovary may have a more complex appearance with cystic or hemorrhagic degeneration
- Doppler findings in torsion are widely variable 3
- little or no intra-ovarian venous flow (common)
- absent arterial flow (less common, but poor prognostic sign)
- absent or reversed diastolic flow
- normal vascularity does not rule out intermittent torsion
- normal Doppler flow can also occasionally be found due to dual supply from both the ovarian and uterine arteries
- whirlpool sign of twisted vascular pedicle 3
- ovary tenderness to transducer pressure 13
Ultrasound has a sensitivity of approaching 100% and specificity of 97% if there is an enlarged ovary with an absence of arterial and venous blood flow 14.
- good at ruling out ovarian torsion if a normal ovary/adnexa is seen on ultrasound
- the twisted ovarian pedicle is pathognomonic for ovarian torsion if demonstrated 11
- torsion appears as a complex adnexal lesion representing
- enlarged ovary (>4.0 cm 11)
- distended pedicle
- possible underlying ovarian lesion
- HU >50 on non-contrast CT suggests hemorrhagic necrosis 2
- lack of enhancement may be seen
- surrounding fat stranding, edema, and free fluid
Not the imaging modality of choice if torsion is suspected, as urgent imaging is required.
If hemorrhagic infarction is present, signal changes include 4:
- thin rim of high signal (methemoglobin) without contrast enhancement
- endometriomas and hemorrhagic corpus luteal cysts are less likely to have a high T1 rim and do not usually involve the entire ovary
- T2: can have low signal due to interstitial hemorrhage
Treatment and prognosis
Urgent surgery is required to prevent ovarian necrosis. Most ovaries are not salvageable, in which case a salpingo-oophorectomy is required. If not removed, the necrotic ovary can become infected and cause an abscess or peritonitis. In the case of a non-infarcted adnexa, surgical untwisting can be performed. Mortality resulting from ovarian torsion is rare. Spontaneous detorsion has also been reported.
For an enlarged edematous ovary +/- Fallopian tube, consider:
- pelvic inflammatory disease (PID): has a very different clinical presentation
- massive ovarian edema (MOO)
- the ovary should be tender to transducer pressure
- absence of ovarian Doppler flow is highly specific for torsion, but normal Doppler flow does not completely rule out torsion
- an ovarian mass causing the torsion must always be sought
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- 9. Warner MA, Fleischer AC, Edell SL et-al. Uterine adnexal torsion: sonographic findings. Radiology. 1985;154 (3): 773-5. Radiology (abstract) - Pubmed citation
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- ovarian torsion
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- ovarian cyst
- corpus luteum
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