This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small Intestine - Crohn's Disease, Subject name: Surgery
[{'content': "Skip lesions are seen in: \nSelect and explain. \nA. Ulcerative colitis, B. Crohn's disease, C. Typhoid, D. Tuberculosis", 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans is 'b' i.e. Crohn's disease FeaturesUlcerative colitisCrohn's ds* Rectal involvement in > 50%> 90%*Rectum spared* Distribution of lesionsContinuous*Skip lesions** Mucosal appearanceFriable, diffusely involvedCobblestone*appearance* Ileal diseaseRare (backwash ileitis)Common* Perianal abcess, fistulasRareCommon* Intestinal strictures & obstructionNot seenCommon* Intestinal fistulasNot seenCommon* Fissures (Radiological)Not seenCommon* UlcersCollar-buttonLinear, cobblestone, fissures* Toxic megacolon*Rare but more than Crohn's dsVery rare* Extraintestinal Manifestation - - Sclerosing pericholangitisCommon*Rare- Uveitis & Arthritis *Common*Common*- Pyoderma gangrenosumCommonRarePathological Features * Depth of inflammationMucosal*,superficialTransmural* ,deep* Creeping mesentric fatNot seenCommon** Fibrous thickening of wallNot seenCommon (lead pipe)** PseudopolypsCommon*Rare* GranulomasNot seenCommon** DysplasiaCommon*Rare* Carcinoma10%*Rare", 'role': 'assistant'}]