Polycystic Ovary Syndrome (PCOS) is a hormonal condition that affects many women of reproductive age. It is characterized by symptoms that result from hormonal imbalances and issues with metabolism. Magnetic Resonance Imaging (MRI) is a medical imaging technique that uses a magnetic field and computer-generated radio waves to create detailed images of the organs and tissues in the body. While it is a useful diagnostic tool, its role in identifying PCOS is specific and supplementary to other methods.
The Primary Tools for PCOS Diagnosis
The diagnosis of Polycystic Ovary Syndrome begins with a clinical evaluation based on the Rotterdam criteria. A diagnosis is confirmed when at least two of three specific conditions are met. These conditions are irregular menstrual cycles indicating ovulatory dysfunction, clinical or biochemical signs of high androgen levels, and the presence of polycystic ovarian morphology on an ultrasound.
Clinical signs of high androgens, or hyperandrogenism, include excess hair growth, acne, and male-pattern baldness. Biochemical signs are confirmed through blood tests that measure hormones like free testosterone. If a person has both irregular periods and signs of hyperandrogenism, an ultrasound may not be necessary for diagnosis but is often performed to get a complete picture.
When imaging is required, transvaginal ultrasound is the standard, first-line tool. This method provides a clear view of the ovaries, allowing a clinician to count small follicles and measure the overall ovarian volume. In PCOS, the ovaries may be enlarged and contain numerous small follicles, often 20 or more, arranged around the periphery. This appearance is frequently described as a “string of pearls.”
When an MRI Becomes Necessary
An MRI is not a routine procedure for diagnosing PCOS; its use is reserved for specific circumstances where more information is needed than other tests can provide. The primary function of an MRI in this context is differential diagnosis. This means its purpose is to rule out other medical conditions that present with symptoms similar to PCOS, such as irregular cycles and high androgen levels. A careful exclusion of these other disorders is a required step before a final diagnosis can be made.
A primary reason to order an MRI is to investigate for an androgen-secreting tumor on the adrenal glands or ovaries. While rare, these tumors can produce high levels of androgens, mimicking the hormonal state of PCOS. Blood tests showing extremely high levels of androgens, such as testosterone or DHEA-S, can point toward a potential tumor and justify the need for more detailed imaging to locate it.
An MRI may also be used when ultrasound results are inconclusive. For example, excess body fat can interfere with the clarity of transabdominal ultrasound images. In adolescent patients who are not sexually active, a transvaginal ultrasound is not appropriate, and a transabdominal ultrasound may not provide sufficient detail. In these cases, an MRI offers a non-invasive alternative for assessing ovarian morphology. A physician might also order an MRI of the head to examine the pituitary gland if a disorder like a prolactinoma is suspected.
What an MRI Can Reveal in PCOS-Related Investigations
An MRI offers better soft-tissue resolution than an ultrasound, allowing for a highly detailed assessment of the ovaries and surrounding structures. The images can distinguish between the supportive tissue (stroma) and the small, fluid-filled sacs (follicles). On T2-weighted MRI images, follicles appear bright, while the stroma has a low signal, making them easy to differentiate.
This level of detail enables a more precise measurement of ovarian volume and an accurate count of follicles, which is helpful when ultrasound results are ambiguous. An MRI can identify a greater number of follicles than ultrasound, providing a more complete picture of the ovarian structure. It can also visualize an increase in the ovarian stroma, another feature associated with PCOS.
The strength of an MRI in a PCOS workup is its ability to visualize other glands and organs. An MRI provides clear images of the adrenal glands, which sit atop the kidneys, allowing a radiologist to identify or rule out a tumor. Similarly, an MRI of the brain can detect small tumors on the pituitary gland. This view ensures a diagnosis of PCOS is not incorrectly made when a different, and potentially more serious, condition is the true cause of the symptoms.