Fig. 4

Microscopic findings of the ovarian mass. Sections of the oval round mass show a a complete structure of the large intestine composed of mucosa (*), submucosa (†), proper muscle (‡), subserosa (bold arrow) and serosa (thin arrow) (H&E). b Mucosa including mucosa muscle (mm), submucosa (sm) and proper muscle (pm) (H&E). c Proper muscle composed of inner circular (IC) and outer longitudinal (OL) layers, myenteric nerve plexus (MNP), subserosa (SS) and serosa (green arrow) (H&E). d A benign teratoma showing sebaceous glands (SG), sweat glands (SwG), and fat tissue (FT) (H&E). e The bone formation (BF) was also noted in the teratoma (H&E). Immunohistochemistry of colon mucosa in the ovarian mass reveals positivity for CK20 (f), and negativity for CK7 (g)