Polycystic Ovary Syndrome (PCOS) is a common endocrine disorder affecting women of reproductive age. It is characterized by a hormonal imbalance leading to symptoms like irregular menstrual cycles and excess androgen levels. Ultrasound imaging is a standard tool used by clinicians during the diagnostic process. Although the name references the ovaries, diagnosis is not based on imaging alone. The ultrasound provides a clear visualization of the ovarian structure, offering key evidence for a proper diagnosis.
The Role of Ultrasound in PCOS Diagnosis
Ultrasound is used to evaluate the specific morphology of the ovaries and exclude other potential causes for a patient’s symptoms. This non-invasive imaging technique allows medical professionals to examine the ovaries for characteristic structural changes associated with PCOS. Scan findings, combined with clinical and biochemical data, help complete the diagnostic picture.
The procedure uses two main approaches: transabdominal or transvaginal ultrasound. A transabdominal scan involves placing the transducer on the lower abdomen and is often used for patients who are not sexually active. The transvaginal approach, inserting a specialized probe into the vagina, is generally preferred. This method provides a much clearer, higher-resolution view of the ovaries and the small structures within them, which is beneficial for accurately counting the tiny follicles.
Ultrasound focuses solely on assessing the physical structure of the ovaries, known as polycystic ovarian morphology (PCOM). A finding of PCOM is not sufficient by itself to confirm a PCOS diagnosis. The imaging results represent only one of the three potential diagnostic criteria and must be interpreted within a multi-criteria assessment.
Visualizing Polycystic Ovaries
The ultrasound image of the ovaries displays specific visual characteristics associated with PCOS. The term “polycystic” refers to numerous small, fluid-filled sacs called follicles, which are immature egg-containing structures, not true cysts. These follicles accumulate because hormonal imbalance prevents them from maturing and being released during ovulation.
Current diagnostic criteria for polycystic ovarian morphology require 20 or more follicles (2 to 9 millimeters in diameter) in at least one ovary. This threshold was updated due to improved ultrasound technology. A second criterion is an increased ovarian volume, defined as greater than 10 milliliters (mL).
These small follicles are often arranged in a specific pattern, described as the “string of pearls” appearance. This visual is created by the follicles lining up just beneath the outer surface of the ovary, surrounding the dense central ovarian stroma. The ovary must be assessed when no dominant follicle or corpus luteum is present, as these structures could temporarily alter the count or volume.
The Complete Diagnostic Picture
A definitive PCOS diagnosis requires more than just visualizing polycystic ovaries. Clinicians use established diagnostic guidelines, such as the Rotterdam criteria, which require a patient to meet two out of three specific conditions, while excluding other medical disorders. This comprehensive approach ensures the diagnosis accurately reflects the underlying endocrine condition.
One criterion is oligo- or anovulation, referring to irregular or absent menstrual periods. Oligomenorrhea means cycles are typically more than 35 days apart, while amenorrhea is the complete absence of a period for several months. This irregular pattern results from hormonal dysfunction preventing regular ovulation.
The third criterion is clinical or biochemical hyperandrogenism, signifying elevated levels of androgens. Clinical signs include hirsutism (coarse hair growth in a male pattern) or severe acne. Biochemical hyperandrogenism is confirmed through blood tests revealing high levels of hormones like total or free testosterone.
Important Considerations and Limitations
The interpretation of an ultrasound for PCOS is subject to several practical considerations and limitations. Diagnosing adolescents is challenging, as they naturally have a high number of ovarian follicles following their first period. Using the polycystic ovarian morphology criterion alone in teenagers can lead to over-diagnosis, so guidelines recommend against using this criterion for those less than eight years past menarche.
Hormonal birth control use can mask or alter the appearance of polycystic ovaries. These medications regulate hormone levels and may reduce the number of visible follicles, potentially leading to a false-negative result. Therefore, the scan should ideally be performed when the patient has not been on hormonal contraceptives for at least three months.
When a transabdominal ultrasound is necessary, proper patient preparation is required for the clearest image. An adequately full bladder is needed to push the uterus and ovaries closer to the abdominal wall for better visualization. However, an overly full bladder can compress the ovaries, leading to an inaccurate calculation of ovarian volume. These factors highlight why the ultrasound must be evaluated by a specialized professional within the broader context of the patient’s full medical profile.