Here's how to differentiate your ascending colon from your rectosigmoid junction. Doctors who treat digestive conditions are accustomed to dealing with a wide variety of conditions, and it's up to you to link the correct diagnoses to the gastroenterology diagnosis and treatment codes. Use the anatomic drawing below to locate the site that your physician addressed, and match that to the sampling of applicable ICD-9 codes in the chart at the bottom of this page.