**5.1 Ovarian endometriosis**

Adnexal localization is the most common clinical setting of endometriosis.

TVUS remains the first diagnostic method in the evaluation of the ovary, generally reserving MRI as a tool for resolving cases in which there is some doubt.

At MRI, a large endometrioma (>1 cm in diameter) appears as a homogeneously hyperintense mass on T1 weighted MR images and show a low signal intensity on T2 weighted MR images with areas of high signal intensity. The 'shading' sign is used to differentiate endometriomas from functional hemorrhagic cysts that do not show it, which usually disappears at subsequent MRI examinations.

Another diagnostic criteria for a definitive diagnosis of endometriomas is the presence of multiple T1 hyperintense cysts regardless of their T2 signal intensity [16].

Endometriomas are often bilateral (more than 50% of cases), multilocular or associated with interovarian adhesions; in the last case a typical MRI pattern called "kissing ovaries" could be noted (**Fig. 4**).

Fig. 4. T2-weighted image acquired on the transverse plane, showing hyperintense bilateral endometrioma masses on the ovaries that are closed up due to interovarian adhesions (Kissing ovaries).

Fat suppression is mandatory to differentiate endometriomas from cystic teratomas.
