A Case of Rectal Endometriosis Presented as Neoplasm

Introduction: A 35-year-old female was admitted with intermittent lower abdominal pain, 8-10 yellow loose stools/day and tenesmus for 1 year. Four months before admission, pain worsened and was associated with dark red bloody stools. The symptoms stopped by the end of menstruation. Colonoscopy at another hospital noted a rectal mass involving half the lumen and pathology showed chronic mucosal inflammation. Enhanced abdominal CT and rectal MRI demonstrated a rectal mass with soft tissue density without clear boundary thought to be consistent with a GIST tumor, adenoma or more likely a malignancy. Past medical history and physical exam were negative except for a 6 cm lower abdominal cesarean scar. Repeat colonoscopy confirmed a mass at the recto-sigmoid junction, about 14-15cm from the anus (Figure 1) and EUS demonstrated wall thickening adjacent to the lesion and irregular echogenicity of mucosa and submucosa with no clear margin. (Figure 2) EMR was carried out, which extruded coffee-like liquid from the lesion and pathology did not offer a definite diagnosis. Because of a concern for GIST she was taken to surgery where a 3.5 -4 cm moderately hard, movable tumor was resected. The final pathology diagnosis was intestinal endometriosis. Discussion: Colonoscopy is helpful in making the diagnosis of rectal endometriosis but the lesions can be misdiagnosed as malignant tumors. While EUS has high sensitivity, its specificity is less accurate. Hormonal therapy is appropriate for patients with mild symptoms but surgery may be needed for more bothersome symptoms, if there is obstruction or when a definitive diagnosis cannot be made by endoscopy as was the case with our patient.Figure 1Figure 2