The case of pathologically proved endometrioma. In most cases, the distinction between endometriomas from other hemorrhagic lesions, such as functional hemorrhagic ovarian cysts, can be difficult. MR findings show the T2 dark spot sign that is specific for chronic hemorrhage and therefore is useful in the diagnosis of ovarian endometriomas. 

The exact cause of this finding is unclear. T2 dark spots may represent chronic retracted blood clots that contain a high concentration of protein and/or hemosiderin.