polycystic ovarian syndrome

Polycystic ovarian syndrome (PCOS), recently referred also as hyperandrogenic anovulation, is a chronic anovulation syndrome associated with androgen excess.

The diagnosis of PCOS generally requires any two of the following three criteria for the diagnosis, as well as the exclusion of other aetiologies (e.g. congenital adrenal hyperplasiaCushing syndrome, and/or an androgen-secreting tumour) :

  • ovulatory dysfunction (oligo- or anovulation)
  • clinical and/or biochemical hyperandrogenism
  • polycystic ovarian morphology on ultrasound
  • Hence, ultrasound is not necessary for the diagnosis if features of both ovulatory dysfunction and hyperandrogenism are present, but will identify the complete PCOS phenotype.


    Hyperandrogenic anovulation has been proposed as a more accurate and potentially less confusing term, as the ovarian feature is of multiple follicles and not cysts . At this stage, however, PCOS remains the term that is widely known and used.


    The estimated prevalence is 8-13% of women of reproductive age but this varies (up to 20%) depending on the diagnostic criteria used .

    Clinical presentation

    The classic triad of PCOS is:

  • oligomenorrhoea
  • hirsutism
  • obesity
  • In addition to this, patients may have infertility, acne, alopecia or biochemically show increased androgen levels.



    Biochemical hyperandrogenism is based on the measurement of free testosterone, free androgen index, or calculated bioavailable testosterone.

    Anti-Müllerian hormone (AMH) levels are generally increased, and there is emerging evidence for the utility of AMH in the diagnosis of PCOS. At the time of writing, there is insufficient assay standardisation and validation, and AMH should not be used in the diagnosis of PCOS at this stage .


    Radiographic features


    Ovaries may be normal in PCOS, and conversely, polycystic ovarian morphology (PCOM) may be seen in women without the syndrome. However, it is well accepted that women with PCOS tend to have larger ovaries with an increased number of follicles.

    The specific diagnostic cut-offs, however, have been the subject of debate and revision in recent years. The updated diagnostic criteria at the time of review are based on a 2018 international consensus guideline .

    In patients >8 years post menarche, and using a high-frequency endovaginal probe:

    If using transabdominal scanning, or older technology where ovarian morphology is not well visualised, consider using the ovarian volume threshold of ≥10 mL on either ovary.

    The diagnostic criteria are adjusted in adolescent females (defined as within 8 years of menarche, or age <20 years) , in whom ultrasound should not be used for the diagnosis of PCOS due to the high incidence of multi-follicular ovaries in this life stage.

    This supersedes the initial Rotterdam criteria of ≥12 follicles and interim recommendations of 24 or 25 follicles per ovary. The presence of a single multifollicular ovary is sufficient to provide the sonographic criterion for PCOS .

    Other morphological features have been described, but do not contribute to formal diagnostic criteria:

    • hyperechoic central stroma
    • peripheral location of follicles (string of pearls sign)
    • follicles of similar size measuring 2-9 mm

    MRI is not warranted routinely in the investigation of PCOS, nonetheless, 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

    History and etymology

    The syndrome was first described by I F Stein and M L Leventhal in 1935 .

    Practical points

    • 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"
    • ultrasound should not be used for the diagnosis of PCOS in patients <8 years after menarche due to the high incidence of multi-follicular ovaries in this life stage
    • as the individual age of menarche may not be known, an age cut-off of 20 years is suggested for the utility of ultrasound in this diagnosis (based on the median age at menarche being approximately 12 years)
    • post menopause, a new or continuing diagnosis of PCOS could be considered based on past history and clinical evidence of persistent hyperandrogenism
    • postmenopausal women presenting with new-onset, severe or worsening hyperandrogenism including hirsutism, require further investigation to rule out androgen-secreting tumours and ovarian hyperthecosis.