Ovarian torsion is a gynaecological emergency presenting as acute onset lower abdominal pain, an enlarged, oedematous ovary with peripherally displaced follicles.
Description
Ovarian torsion is a gynaecological emergency characterised by the partial or complete rotation of the ovarian pedicle, leading to obstruction of lymphatic and venous outflow and, if left untreated, arterial inflow. This can result in ovarian ischaemia and necrosis. It is most commonly associated with ovarian masses, which act as a pivot for the rotation. The term “torsion” refers to the twisting of the ovary, which can also involve the fallopian tube, a condition also known as adnexal torsion.
Pathogenesis
Ovarian torsion results from the rotation of the ovary on its ligamentous supports, the infundibulopelvic ligament and the utero-ovarian ligament. This leads to venous, lymphatic, and eventually arterial occlusion. Early stages are characterised by oedema and haemorrhage within the ovary, progressing to necrosis if the torsion remains untreated.
Subtypes
Ovarian torsion can be classified into two main subtypes based on the presence or absence of an ovarian mass:
- Torsion on Normal Ovary: More common in prepubertal and adolescent females.
- Torsion on Ovary with Mass: More common in reproductive-aged women; the mass can be benign or malignant.
Epidemiology, Risk Factors & Associations
- Most common in reproductive-aged women (20-40 years).
- Greatest risk factor: presence of ovarian cyst or mass (80% of cases).
- Associations: polycystic ovarian syndrome, ovarian hyperstimulation syndrome, and pregnancy (first trimester).
- Pregnancy: associated with increased risk due to enlarged ovaries from corpus luteum cysts.
Clinical Features
- Acute onset of unilateral lower abdominal pain.
- Nausea and vomiting.
- Fever and tachycardia in advanced cases.
- Pathognomonic sign: Sudden relief of pain may indicate ovarian necrosis.
Complications
- Ovarian necrosis.
- Infertility if bilateral torsion or subsequent oophorectomy.
- Risk of malignant transformation is low, given that most associated masses are benign.
Pathological Features
Histopathology
- Macroscopic: Enlarged, oedematous ovary with possible surface haemorrhages.
- Microscopic: Ovarian stromal oedema, haemorrhage, and necrosis in late stages.
Serology
- Non-specific.
Biochemistry
- Elevated white cell count; inflammatory markers may be raised.
Radiological Features
General Features
- First-line investigation: Ultrasound with Doppler.
- Gold standard: MRI for unclear cases. More sensitive for detecting ovarian oedema, stromal haemorrhage, and twisted vascular pedicle.
- Most sensitive finding is asymmetric ovarian enlargement (typically > 26 mL in reproductive women)
- Abnormal ovarian positioning (midline, anterior to uterus, in the cul-de-sac, contralateral adnexa)
- Uniformly peripherally displaced follicles (string of pearls sign)
- Free fluid in the pelvic cul-de-sac
- Right ovary is more commonly affected (thought to be due to protective effect of sigmoid colon on the left)
- Assess for lead point; benign cystic teratoma is the most common (cystic lesion with a Rokitansky nodule)
CT
- Non-contrast: Enlarged ovary with whirling of the ovarian pedicle.
- C+ Arterial and Venous: May show lack of enhancement in cases of arterial compromise.
MRI
- T1: High signal intensity may indicate haemorrhage.
- T2: Heterogeneous signal intensity due to oedema and haemorrhage.
- FLAIR: Useful for identifying free fluid in the pelvis.
- DWI/ADC: Restricted diffusion may be seen in necrotic areas.
- T1 Gad+: Absent or reduced enhancement in affected ovary.
- SWI/GRE/T2*: May demonstrate haemorrhagic components.
US
- B-mode:
- Hallmark enlarged ovary (> 10 mL volume) with uniformly peripherally displaced follicles (string of pearls sign)
- Peripheral displacement due to central medullary oedema
- Follicular ring sign represents 2 mm thick echogenic ring surround follicles
- Heterogeneous stromal echotexture from haemorrhage and oedema.
- Free fluid in the cul-de-sac.
- Assess for lead point – associated cyst or neoplasm. Lead point mass may also demonstrate an echogenic oedematous ring sign.
- Colour Doppler:
- Reduced (ovary has dual supply from ovarian or uterine arteries) or absent arterial and venous flow.
- Torted vascular pedicle (whirlpool sign).
NM
- PET FDG: Not typically used in the diagnosis of ovarian torsion.
Grading and Staging
Not applicable to ovarian torsion as it is an acute surgical condition rather than a neoplastic process.
Diagnosis
Diagnosis is primarily clinical, supported by ultrasound findings of an enlarged ovary with absent or reduced blood flow on Doppler. MRI is reserved for unclear cases.
Differential Diagnosis
- Fallopian tube or parfimbrial cyst torsion
- Ovarian cyst rupture.
- Ectopic pregnancy.
- Pelvic inflammatory disease.
- Appendicitis.
Management
Immediate referral to gynaecology for surgical evaluation is crucial. The mainstay of treatment is laparoscopy to detorse the ovary and assess viability. Oophorectomy is considered if the ovary is necrotic.