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Ovarian torsion

Ovarian torsion (also sometimes termed adnexal torsion) refers to rotation of the ovary and portion of the Fallopian tube on the supplying vascular pedicle (also termed tubo-ovarian torsion). 

This can be intermittent or sustained and results in venous, arterial and lymphatic stasis. It is a gynaecologcial emergency and requires urgent surgical intervention to prevent ovarian necrosis. 

Epidemiology

Ovarian torsion has a bimodal age distribution occurring mainly in young women (15-30 years) and in post-menopausal women. Approximately 20% of the cases occur during pregnancy 1.

Torsion occurs for two main reasons 2

  • hypermobility of the ovary: <50%
  • adnexal mass: ~50-80%

Clinical presentation

Most patients present with severe nonspecific lower abdominal and pelvic pain, nausea, and vomiting. There is adnexal tenderness. A raised white cell count is common.

Presentation of torsion can be either intermittent or sustained.

Pathology

The end result of the vascular compromise of ovarian torsion is haemorrhagic infarction and necrosis. This can occur within hours of torsion onset.  

Torsion of a normal ovary more commonly occurs in young children when developmental abnormalities may be implicated in the pathogenesis, such as excessively long Fallopian tubes or an absent mesosalpinx.

In adulthood, causes include both benign and malignant ovarian tumours, polycystic ovaries and adhesions. In early pregnancy a torsion can occur secondary to a corpus luteum cyst or laxity of the adjacent tissues.

Radiographic features

The main feature of torsion is ovarian enlargement due to venous/lymphatic engorgement, oedema and haemorrhage. 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 generally unilateral, with a slight (3:2) right-sided predilection (presumably due to effects of the sigmoid colon being on the left) 6,8.

Ultrasound

Ultrasound is the 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 haemorrhagic degeneration
Doppler 3
  • Doppler findings in torsion can be widely variable
    • 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 exclude 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

The ovary should be tender to transducer pressure 13.

CT
  • good at ruling out ovarian torsion if a normal ovary/adnexa is seen
  • 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 haemorrhagic necrosis 2
  • lack of enhancement may be seen
  • surrounding fat stranding, oedema, and free fluid
Pelvic MRI

Not the imaging modality of choice if torsion is suspected, as urgent imaging is required.

If haemorrhagic infarction is present, signal changes include 4:

  • T1
    • thin rim of high signal (methaemoglobin) without contrast enhancement
    • endometriomas and haemorrhagic corpus luteal cysts are less likely to have high T1 rim and do not usually involve the entire ovary
  • T2: can have low signal due to interstitial haemorrhage

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 abscess or peritonitis. In the case of a non-infarcted adnexa, surgical untwisting can be performed. Mortality resulting from ovarian torsion is rare. Spontaneous de-torsion has also been reported.

Differential diagnosis

For an enlarged oedematous ovary +/- Fallopian tube, consider:

Practical points

  • 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 exclude torsion
  • an ovarian mass causing the torsion must always be sought

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