What is the appearance of endometriomas on MRI?

The characteristic MRI finding is a cystic mass with contents of high signal intensity on T1-weighted images and low signal intensity on T2-weighted images.
The lowered signal intensity on T2-weighted images is caused by the paramagnetic effect of old blood due to recurrent hemorrhage. This finding is called T2 shading. High signal intensity on a fat-suppression sequence (not fat)