A 25-year-old female with an endometriotic cyst on her left ovary came to our hospital, claiming she had bloody stool, fever, and abdominal pain. We diagnosed her with an endometriotic cyst infection and gave her antibiotics, which eased the condition. We also performed a colonoscopy to examine the bloody stool, in which we discovered a submucosal tumor and a pine cone-like elevation in her rectosigmoid colon. Based on the biopsy of the lesion, we diagnosed it as intestinal endometriosis because of ER (+) , PgR (+) , and CDX - 2 (-) . After the episode, the patient continued to have blood stool at each menstruation. Therefore, we put her on an ultra low dose birth-control pill, and the symptom has receded.
It is hard to diagnose intestinal endometriosis by biopsy because of the location of the main lesion and the poor pathological characteristics in normal staining. However, in this case, by suspecting it from clinical course and communicating it to the pathologist, we could diagnose it from biopsy by adding immunostaining, enabling us to successfully treat it conservatively.
