This ultrasound case shows many of the typical features of an ovarian torsion. The ovary is distended with absent Doppler flow and some adjacent free fluid. The ovary also contains a 4 cm dermoid cyst with an echogenic Rokitansky nodule ('dermoid plug').  

Around 50% of torsions occur in ovaries which contain a lesion and around 50% of these are dermoid cysts.