Compound melanocytic nevus arising in a mature cystic teratoma of the ovary

A 28-year-old woman complained of irregular menstruation. Abdominal ultrasound and magnetic resonance imaging (MRI) examinations revealed a cystic tumor in the left ovary. A histological examination of the resected ovary revealed that the lesion was a mature cystic teratoma. In this tumor, components such as skin with appendages, a thyroid gland, mucosa of the digestive tract and a submandibular gland were observed. Interestingly, compound melanocytic nevus was also present in the skin component. To the best of our knowledge, this is the sixth reported case of nevus arising in a mature cystic teratoma of the ovary. Despite the extreme rarity of such a lesion, pathologists should recognize the possibility of such lesions occurring in ovarian teratoma.