# Magnetic Resonance Roadmap in Detecting and Staging Endometiosis: Usual and Unusual Localizations
## 5 Adenomyosis  
Adenomyosis is a disease characterized by the presence of endometrial tissue (glands and stroma) in the context of the myometrium. It is much more common in pluripares and in women undergoing surgery of the uterus [60]. Generally, women complain of extremely severe pain during menstruation and suffer from abdominal cramps, abundant and irregular menstruation, fertility problems and adverse pregnancy outcomes [61,62]. Over the years, authors have proposed different classifications that could collate the different facets of adenomyosis. Among the most recent and complete classifications is the one proposed by [PERSON] et al., which specifically selected five parameters to describe the disease: (1) the affected area (internal adenomyosis or external adenomyosis); (2) the pattern (diffuse or focal); (3) the size; (4) the location; and (5) the concomitance of other localization of endometriosis or other gynecological pathologies [63]. In order to discuss internal endometriosis, it is essential to introduce the concept of the junctional zone. The junctional zone represents the intermediate layer of the myometrium, which typically exhibits a low signal intensity on T2 WI sequences, and appears as a continuous structure under normal physiological conditions [64,65]. The thickness of the junctional zone can vary throughout a woman's life based on factors such as age and hormonal therapies. Additionally, it undergoes slight changes on a monthly basis in accordance with the different phases of the menstrual cycle [66,67]. The agreement among the authors is that a thickening of the junction zone (>12 mm) serves as an indirect indication of internal adenomyosis. Nevertheless, according to the recent literature, this particular sign cannot be considered conclusive evidence of the disease on its own. It is, therefore, advised to assess two additional parameters for a comprehensive evaluation [68]:  
* The parameter known as \"rationalx\" corresponds to the ratio between JZmax and the total thickness of the myometrium, with a value exceeding 40% typically considered an acceptable diagnostic parameter [68];
* The parameter called \"JZ differential\" (JZdiff) measures the maximum and minimum thickness difference between the anterior and posterior uterine walls, where a value greater than 5 mm is indicative [68]. The aforementioned criteria serve as indirect indicators that can aid radiologists in reporting cases of internal adenomyosis (Figure 9). On the other hand, direct criteria include the observation of cystic areas (hyperintense on T2 WI) and/or hemorrhagic foci (hyperintense on fat-suppressed T1 WI and T1 WI) within the inner layer of the myometrium [67,69] (Figure 10). The ENDOVALIRM group considers external adenomyosis as part of mediocentral localization of DIE, both in anterior and posterior subtypes. The external adenomyosis corresponds to an extrinsic involvement of the outer myometrial layers. It is more common that external adenomyosis involves the posterior compartment in association with a severe involvement of the rectum-vaginal space [39]. On T2 WI, an irregular thickening of the subserosal myometrium is observed, sometimes in association with hyperintense spots that correspond to cystic components. Another fundamental criterion is the presence of blood components, which can be evaluated in the sequences weighed on T1 [69,70] (Figures 5 and 9). However, there are instances where adenomyosis can be localized, known as adenomyoma. It is crucial to accurately differentiate adenomyosis from uterine fibroids, as fibroids often cause more noticeable distortion of the uterine contour and exhibit greater differentiation from the surrounding myometrium. This distinction may also be aided by the presence of a pseudocapsule in fibroids [71]. It is also important for differential diagnosis, even with transient uterine contractions. During uterine contractions, a temporary localized area of decreased signal intensity can occur along with thickening of the junctional zone.