Polycystic ovaries (PCO) is an imaging descriptor of a particular type of change in ovarian morphology. A proportion of women with polycystic ovaries will have the polycystic ovarian syndrome (PCOS), which in turn requires additional clinical, as well as biochemical, criteria. Otherwise PCO can be considered a normal variant.
PCO may be seen in ~20% women of reproductive age 1,4.
Transvaginal ultrasound is considered the gold standard in the diagnosis of polycystic ovaries. Features can affect either one (unilateral polycystic ovary) or both ovaries.
- presence of >25 follicles per ovary (superseding the earlier Rotterdam criteria of 12 or more follicles)
- individual follicles are generally similar in size and measure 2-9 mm in diameter 7
- peripheral distribution of follicles; this can give a "string of pearls" appearance
- background ovarian enlargement (volume greater than 10 mL) 7
- central stromal brightness +/- prominence
* A study published in 2013 suggested that the number of follicles in each ovary- FNPO (follicle number per ovary) is a more sensitive and specific criteria for diagnosis of the PCO compared with numbers of follicles in cross section-FNPS (follicle number per section) or ovarian volume- OV. This study showed an FNPO threshold of 26 follicles had sensitivity of 85% and specificity of 94% when discriminating between controls and PCOS. A FNPS threshold of nine follicles had a 69% sensitivity and 90% specificity, and an OV of 10 cm3 had a 81% sensitivity and 84% specificity 11.
Pelvic MRI may show most or all of the above sonographic features. Signal characteristics include:
- T1: small uniform follicles are low in signal while the central stroma is of intermediate signal (vs normal myometrium)
- T2: follicles have high T2 signal while the central stroma is of comparatively low T2 signal 8
General imaging differential considerations include:
- multifollicular ovaries (MFO): fewer cysts (~6 or more per ovary), which tend to be larger (up to 10 mm in diameter) and distributed throughout the ovary with no stromal hypertrophy 2
- with a lack of consensus sometimes it is easier to report the number of follicles in each ovary rather than attempt to label the ovaries as "polycystic" or "multifollicular"
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- 7. Barber TM, Alvey C, Greenslade T et-al. Patterns of ovarian morphology in polycystic ovary syndrome: a study utilising magnetic resonance imaging. Eur Radiol. 2010;20 (5): 1207-13. doi:10.1007/s00330-009-1643-8 - Pubmed citation
- 8. Semelka RC. Abdominal-Pelvic MRI. Wiley-Blackwell. (2010) ISBN:0470487755. Read it at Google Books - Find it at Amazon
- 9. Resource from : Specialsed Obstetric and Gynaecological Imaging Australia : SOGI www.sogi.net.au
- 10. Phy J, Foong S, Session D et-al. Transvaginal ultrasound detection of multifollicular ovaries in non-hirsute ovulatory women. Ultrasound Obstet Gynecol. 2004;23 (2): 183-7. doi:10.1002/uog.954 - Pubmed citation
- 11. Lujan ME, Jarrett BY, Brooks ED et-al. Updated ultrasound criteria for polycystic ovary syndrome: reliable thresholds for elevated follicle population and ovarian volume. Hum. Reprod. 2013;28 (5): 1361-8. doi:10.1093/humrep/det062 - Pubmed citation
- 12. Martins WP, Kollmann M, Raine-Fenning N. Counting ovarian follicles: updated threshold for diagnosis of hyperandrogenic anovulation. Ultrasound Obstet Gynecol. 2014;44 (2): 131-4. doi:10.1002/uog.13402 - Pubmed citation