Role of Ultrasound and Magnetic Resonance Imaging in diagnosis of Polycystic Ovarian Syndrome

Abstract

Summary The polycystic ovarian syndrome (PCOS) is now recognized as the most common endocrine abnormality in women of reproductive age, there is still no universal consensus on diagnostic criteria for PCOS, and its etiology remains incompletely understood. Women with PCOS are at an increased risk for infertility, hypertension, hyperlipidemia, type 2 diabetes mellitus, coronary artery disease, and cerebral vascular disease. The diagnosis of PCOS is made on the clinical, biochemical and sonographic findings; sonographic findings alone are not specific. According to Rotterdam criteria 2 of the following criteria are required for the diagnosis of PCOS : 1. Oligo- or anovulation 2. Hyperandrogenism (clinical or biochemical) and 3. Polycystic ovaries - on imaging As well as the exclusion of other etiologies, such as congenital adrenal hyperplasia, Cushing syndrome and / or an androgen secreting tumour. Ultrasound is the imaging modality of choice for PCO detection. Transabdominal ultrasound has been largely superseded by transvaginal scanning because of greater resolution and in many cases patient preference, as the need for a full bladder is avoided which saves time and may be more comfortable. Transvaginal ultrasound considered the gold standard in the diagnosis of polycystic ovaries. Ultrasonographic features include: • Presence of 10-12 or more follicles • Individual follicles are generally similar in size and measure 2-9 mm in diameter. • Peripheral distribution of follicles - this can give a "string of pearls" appearance. • Background ovarian enlargement(volume greater than10cc). • Central stromal brightness. +/- prominence. Only one ovary fitting these criteria is sufficient to define PCO. If there is evidence of a dominant follicle (>10 mm) or a corpus luteum, the scan should be repeated during the next cycle.

Pelvic MRI may show most or all of the above ultrasonographic features. MR imaging may be helpful in cases in which transvaginal US cannot be performed and transabdominal US does not offer adequate visualization (eg, in cases of extreme obesity). T2 weighted images in transverse and coronal planes are the best means of studying the ovaries, and show counting peripheral cysts more clearly. Ultrasonography is also preferred for stromal assessment. MRI does not provide any extra information as compared to ultrasonography . The main role of MRI is to exclude small virilising tumors. Signal characteristics include: • T1 - the small uniform follicles are low in signal while the central stroma is of low to intermediate signal (e.g. compared with normal myometrium). • T2 - follicles show high T2 signal while the central stroma is of low T2 signal. Differential diagnosis: • Multi-follicular ovaries (MFO) : with Larger follicles, lesser stromal echodensity, normal ovarian volume, also a dominant follicle is probably seen. Color Doppler shows the changes of vascularization in PCO in the intraovarian helical vessels (eg. higher uterine pulsatility index (PI)). Three-Dimensional Ultrasound can measure the accurate ovarian volume.