**8. Histological features of the secondary Mullerian system**

The secondary Mullerian system consists of the covering mesothelial layer and the submesothelial mesenchyme, on and adjacent to the ovaries, the pelvic peritoneum, the omentum and the retroperitoneal lymph nodes. The most common type of epithelial differentiation is a tubal-like epithelium, with ciliated cells. In the omentum and the ovaries cystic inclusions of tubal type epithelium are often observed intermingled with endometrialtype epithelium. Differentiations to mucinous, transitional and squamous type epithelial lesions, benign and malignant are also described. The sub-mesothelial stroma retains the ability to differentiate towards endometrial stroma and smooth muscle tissue and to undergo decidual reaction.
