This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdominal Radiography, Subject name: Radiology
[{'content': "Radiological signs of crohn's disease: \nSelect and explain. \nA. String sign of cantor, B. Pipestem appearance, C. Pseudo polyp, D. Backwash ileitis", 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans, A. (String sign of cantor) Characteristic Radiological features of Crohn's disease or Regional Enteritis:Terminal ileum is the MC siteGranularity' & asymmetrical involvement with skip lesionUlcer: Apthous ulcer & fissure ulcerCobblestone pattern (serpiginous longitudinal + transverse ulcer separated by areas of edema)Rigidity' of mesenteric boarder and pseudosacculation of antimesenteric boarder (Omega sign)Wide gapping of bowel loops due to thickening of bowel wallStricture : long segment (string .sign if cantorDoule Halo configuration is seen on CT scan (Radiology review manual by wolfgang Dahnert 5th/809) Characteristic features of ulcerative colitisCollar button ulcerDouble Trackingflongitudinal submucosal ulceration over several centimeter)Symmetrical involvement of colonRectum involved in 95% of casesThumbprinting due to mucosal oedemBlunting of haustral fold (Pipestem appearance)Inflammatory palypBackwash ileitis: In ulcerative colitis when whole colon involved, the inflammation extends 1-2 cm into terminal ileum in 10-20% cases called Backwash ilitis .", 'role': 'assistant'}]