27 The first is the inner lining of the uterus, or endometrial zone, followed by the junctional zone (JZ), and then the myometrial zone. On T2-weighted images, the endometrium normally exhibits high signal intensity, whereas the surrounding JZ exhibits relatively low signal intensity. The remainder of the myometrium is generally characterised by intermediate signal on T2 imaging (39,40). On T1 images, it is also possible to visualise potential haemorrhagic areas within the uterine structure, such as those sometimes seen in adenomyomas (41). As adenomyosis is thought to arise from the disruption and thickening of the JZ, the standard MRI imaging techniques used are thus T1- and T2- weighted MRI, which are most effective in identifying potential anomalies in the JZ. Unlike with TVUS, which has the MUSA criteria, there are no accepted classification or diagnostic criteria when evaluating an MRI for presence of adenomyosis. While much has been reported about typical, atypical, direct and indirect MRI manifestations of adenomyosis (17,33,42), the recognition of these features often still depends on the professional analysing the images. Several different classifications of adenomyosis have been suggested based on these differing criteria (17,43), but few objective guidelines for adenomyosis exist. The most widely reported objective measures are based on the appearance of JZ, with a thickness of over 12mm, a difference > 5mm between maximum and minimum JZ diameter, and a ratio of >40% of JZ to the full myometrium thickness thought to signify adenomyosis (34,36,40,44). These criteria are still not widely accepted however, with the 12mm cut-off value recently coming into question (45). This highlights the need for further characterisation of adenomyosis on MRI. Evaluation of the JZ can also be problematic as its thickness changes during the menstrual cycle and is affected by hormonal fluctuations, which can limits the ability to distinguish between ‘normal’ JZ and adenomyosis foci (42,46–48). Furthermore, uterine contractions during MRI can give a false impression of (focal) adenomyosis (42). Other examples of how adenomyosis can be objectified on MRI include uterine volume, uterine wall thickness or the volume or size of (suspected) adenomyotic foci (4,33,40,49,50). Some studies have also attempted to correlate MRI characteristics of adenomyosis with clinical outcomes, such as dysmenorrhoea, treatment response or obstetric outcomes (4,49,51–54), but it is unclear if
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