比較Ulcerative colitis及Crohn's colitis，下列敘述何者錯誤？
gross appearance : Ulcerative colitis較多有thickened colon wall
microscopic appearance : Crohn's colitis常有lymphoid aggregates
clinical features : Ulcerative colitis較常有血便
operative treatment : Crohn's colitis是ileal pouch的contraindication
