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 polycystic ovaries can be considered a normal variant.
Polycystic ovaries 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, the follicle number per ovary (FNPO) is a more sensitive and specific criteria for diagnosis of PCO, as compared with the numbers of follicles in cross section, also known as follicle number per section (FNPS), or ovarian volume. This study showed an FNPO threshold of 26 follicles had a 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 ovarian volume of 10 mL 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"
- 1. Lakhani K, Seifalian AM, Atiomo WU et-al. Polycystic ovaries. Br J Radiol. 2002;75 (889): 9-16. Br J Radiol (full text) - Pubmed citation
- 2. Adams J, Franks S, Polson DW et-al. Multifollicular ovaries: clinical and endocrine features and response to pulsatile gonadotropin releasing hormone. Lancet. 2 (8469-70): 1375-9. - Pubmed citation
- 3. Atiomo WU, Pearson S, Shaw S et-al. Ultrasound criteria in the diagnosis of polycystic ovary syndrome (PCOS). Ultrasound Med Biol. 2000;26 (6): 977-80. Ultrasound Med Biol (link) - Pubmed citation
- 4. Hart R, Hickey M, Franks S. Definitions, prevalence and symptoms of polycystic ovaries and polycystic ovary syndrome. Best Pract Res Clin Obstet Gynaecol. 2004;18 (5): 671-83. doi:10.1016/j.bpobgyn.2004.05.001 - Pubmed citation
- 5. Jonard S, Robert Y, Cortet-rudelli C et-al. Ultrasound examination of polycystic ovaries: is it worth counting the follicles? Hum. Reprod. 2003;18 (3): 598-603. Hum. Reprod. (link) - Pubmed citation
- 6. Michelmore KF, Balen AH, Dunger DB et-al. Polycystic ovaries and associated clinical and biochemical features in young women. Clin. Endocrinol. (Oxf). 1999;51 (6): 779-86. Clin. Endocrinol. (Oxf) (link) - Pubmed citation
- 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
- 13. Lee TT, Rausch ME. Polycystic ovarian syndrome: role of imaging in diagnosis. (2012) Radiographics : a review publication of the Radiological Society of North America, Inc. 32 (6): 1643-57. doi:10.1148/rg.326125503 - Pubmed