Ovarian mature cystic teratoma is a common ovarian neoplasm with rich fat content and is easily confirmed on MRI. 

A Rokitansky nodule is seen as a round structure protruding into the cyst lumen. The appearance of dermoid cyst is such case resembles the appearance of "Poké ball" made by the Rokitansky nodule and the fat fluid level, that usually described as "floating ball sign". This appearance is characteristic for mature cystic teratoma of the ovary.