RESUMEN
Endometriosis is described as the presence of functioning endometrial tissue at sites outside the uterus. Up to 15% ofwomen in their reproductive period are affected by this condition. Endometriosis is mostly foundon the uterosacral ligaments, inside the rectovaginalseptum or vagina, in the rectosigmoid area, ovarianfossa, pelvic peritoneum, ureters, and bladder, causinga distortion of the pelvic anatomy. Colonic involvement is rare but is usually found at the level of the rectum or the sigmoid colon. Acute presentation with intestinal obstruction or perforation is rare. While malignant transformation of endometrial lesions is rare, findings of dysplasia on pathology sections can give rise to questions of management. Immunohistochemistry and electron microscopy can help decision making. We present the case of a 38 year old woman with intestinal obstruction caused by sigmoid colon endometriosis with moderate dysplasia in which transmission electron microscopy was used for postoperative diagnosis. Detailed analysis of these cases, while logistically difficult, can prove useful in understanding the etiology and pathophysiology of the disease.