Vienna classification of Crohn’s disease
| *Maximum extent at any time before first resection. | |
| †Limited to the terminal ileum with or without spill over into the caecum. | |
| ‡Any disease location proximal to the terminal ileum regardless of additional involvement. | |
| ¶Occurrence of constant luminal narrowing (radiological, endoscopic, or surgical) with prestenotic dilatation or obstructive signs, without penetrating disease, at any time in the course of the disease. | |
| §Occurrence of intra-abdominal or perianal fistulas, inflammatory masses, and/or abscesses at any time in the course of the disease. Perianal ulcers, but not skintags, are also included. | |
| Age at diagnosis | A1, <40 years |
| A2, >40 years | |
| Location* | L1, terminal ileum† |
| L2, colon | |
| L3, ileocolon | |
| L4, upper gastrointestinal tract‡ | |
| Behaviour | B1, non-stricturing non penetrating |
| B2, stricturing¶ | |
| B3, penetrating§ | |