MRI appearances of bladder endometriosis.

Endometriosis is characterized by endometrial tissue in ectopic foci outside the uterus. Involvement of the urinary tract is rare, with the bladder being most commonly affected in these cases. Radiologically these lesions, which are usually small, may be difficult to distinguish from intrinsic bladder neoplasia. Four cases of vesical endometriosis are presented with the MRI features that suggest the diagnosis.