Vienna classification of Crohn’s disease
| Adapted from Gasche and colleagues.5 |
| Age at diagnosis |
| Age when diagnosis of Crohn’s disease was first definitively established by radiology, endoscopy, pathology, or surgery. |
| • A1—<40 y |
| • A2—⩾40 y |
| Location |
| Maximum extent of disease involvement at any time before the first resection. Minimum involvement for a location is defined as any aphthous lesion or ulceration. Mucosal erythema and oedema are insufficient. For classification, at least both a small bowel and a large bowel examination are required. |
| • L1—Terminal ileum |
| ‐ Disease limited to the terminal ileum (the lower third of the small bowel) with or without spill over into the caecum. |
| • L2—Colon |
| ‐ Any colonic location between the caecum and rectum with no small bowel or upper gastrointestinal (GI) involvement. |
| • L3—Ileocolon |
| ‐ Disease of the terminal ileum with or without spill over into the caecum and any location between the ascending colon and rectum. |
| • L4—Upper GI |
| ‐ Any disease location proximal to the terminal ileum (excluding the mouth) regardless of additional involvement of the terminal ileum or colon. |
| Behaviour |
| • B1—Non-stricturing non-penetrating |
| ‐ Inflammatory disease which never has been complicated at any time in the course of disease. |
| • B2—Stricturing: |
| ‐ Stricturing disease is defined as the occurrence of constant luminal narrowing demonstrated by radiological, endoscopic, or surgical-pathological methods, with prestenotic dilatation or obstructive signs/symptoms without the presence of penetrating disease at any time in the course of disease. |
| • B3—Penetrating: |
| ‐ Penetrating disease is defined as the occurrence of intra-abdominal or perianal fistulas, inflammatory masses, and/or abscesses at any time in the course of disease. Perianal ulcers are also included. Excluded are postoperative intra-abdominal complications and perianal skin tags. |