Which of the following would be the best morphological feature to distinguish ulcerative colitis from Crohn's disease -
Pseudopolyps (inflammatory polyps) can be seen in both Crohn's disease and ulcerative colitis
In ulcerative colitis, the distribution of these pseudopolyps can be diffuse but in Crohn's disease, the distribution cannot be diffuse because a classic feature of crohn's disease is the sharp demarcation of diseased bowel segments from the adjacent uninvolved bowel. When multiple bowel segments are involved the intervening bowel is essentially normal (skip lesions).

Mucosal edema
- The hallmark of both ulcerative colitis and crohn's disease is mucosal inflammation and chronic mucosal damage. So mucosal edema is a feature of both of these diseases.
- The important point is that while in Ulcerative colitis these processes are limited to mucosa or submucosal, in crohn's disease these processes extend beyond the mucosa and submucosa and involves the entire wall.

Crypt abscesses -

- Crypt abscesses are produced due to infiltration of the neutrophil into crypt lumen.
- These crypt abscesses are not specific for ulcerative colitis and may be observed in crohn's disease or any active inflammatory colitis.

Lymphoid aggregates in mucosa

The characteristic mucosal feature of idiopathic inflammatory bowel disease on histology includes —
i. Distortion of crypt architecture
ii.Destruction and loss of crypt
iii.A marked increase in lymphocytes and plasma cells in lamina propria.
iv. These features are specific to inflammatory bowel disease and help to differentiate idiopathic inflammatory bowel disease from acute infectious colitis and other chronic colitis.
Diffuse distributions of pseudopolyps
Mucosal edema
Crypt abscesses
Lymphoid aggregates in the mucosa