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Table 1 Montreal classification

From: Comparative perianal fistula closure rates following autologous adipose tissue-derived stem cell transplantation or treatment with anti-tumor necrosis factor agents after seton placement in patients with Crohn’s disease: a retrospective observational study

Classification Description
Age of onset (A)
 A1 16 years old or younger
 A2 17-40 years old
 A3 Over 40 years old
Location (L)
 L1 Terminal ileum
 L2 Colon
 L3 Ileocolon
 L4 Upper gastrointestinal
Behavior (B)
 B1 Non-stricturing, non-penetrating
 B2 Stricturing
 B3 Penetrating