This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Small & Large Intestine, Subject name: Surgery
Earliest change seen in Crohn's disease: 
Select and explain. 
A. Aphthous ulcer, B. Serpiginous ulcer, C. Crypt abscess, D. Mesenteric wrapping
A: Aphthous ulcer
Answer: A: Aphthous ulcer 
Explanation: Ans. (a) Aphthous ulcersRef: Surgery Sixer 2nd edition, Page 420Pathologic features:Crohn's diseaseUlcerative colitis* Transmural inflammation* Noncaseating granulomas* Aphthous ulcers are the earliest manifestation* Serpiginous/Bear claw linear ulcers* Cobblestone appearance* Skip lesions* Fistulas* As the disease progresses, the mucosa begin to erode leaving only small islands of mucosa that resemble polyps but are actually pseudo polyps* Crypt abscesses* Confined to the mucosa and submucosa, in the most severe forms of the disease, such as fulminant colitis or toxic megacolon, the disease process may extend to the deeper muscular layers of the colon and even to the serosa(Crypt abscess and pseudopolyps can also occur in Crohn's disease but less common than ulcerative colitis )