Fig. 2

Microscopic lesions in case of endometrioma in a bitch. a Endometrioma presenting epithelial tissue in detail (arrow) similar to the endometrium forming tubules, acini or cavity structures filled with blood and surrounded by intense stroma (Hematoxylin and eosin, bar = 250 μm). b Epithelium with particulate and eosinophilic material at the apical surface, consistent with secretion (Periodic Acid-Schiff, bar = 24 μm). c Fibers of smooth muscle forming the stroma of the endometrioma (asterisk) (Masson trichrome, bar = 250 μm). d Extensive areas of bleeding in the stroma and within the lumen of tubules coated with endometrial epithelium (Hematoxylin and eosin, bar = 250 μm)