What histological features are most specific for diagnosing CD in fulminant colitis specimens

What is known

- In a blinded re-evaluation of fulminant IBD colectomy specimens, granulomas and lymphoid aggregates were the two most specific indicators of Crohn's disease. ^1,2 - Granulomas and transmural lymphoid hyperplasia/aggregates, especially when not in areas of ulceration, are the two most specific indicators of Crohn's disease in fulminant colectomy specimens; poorly formed microgranulomas may also be good indicators. ^3,4 - Features classically regarded as typical of Crohn's disease such as linear ulceration and fissures are relatively common in fulminant colitis regardless of cause and are not specific indicators of Crohn's disease. ^1,4

What is unknown / caveats

- Histopathology alone has limited accuracy in fulminant IBD; microscopy correctly classified only 87% of cases and interobserver diagnosis changed in ~22% - Transmural inflammation and fissuring ulceration overlap with severe colitis of any etiology and are non-specific - Even the most specific features do not fully resolve classification, and a subset of specimens remain indeterminate.

## References

1. Swan NC, Geoghegan JG, O'Donoghue DP, Hyland JM, Sheahan K. Fulminant colitis in inflammatory bowel disease: detailed pathologic and clinical analysis. Dis Colon Rectum. 1998;41(12):1511-5. PMID: 9860331.

2. Geboes K, Colombel JF, Greenstein A, Jewell DP, Sandborn WJ, Vatn MH, Warren B, Riddell RH. Indeterminate colitis: a review of the concept--what's in a name?. Inflamm Bowel Dis. 2008;14(6):850-7. PMID: 18213696.

3. Nicholls RJ, Wells AD. Indeterminate colitis. Baillieres Clin Gastroenterol. 1992;6(1):105-12. PMID: 1586764.

4. Guindi M, Riddell RH. Indeterminate colitis. J Clin Pathol. 2004;57(12):1233-44. PMID: 15563659.

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_Draft, generated by the IBDology RAG and not yet clinician-reviewed. Answers are grounded in the retrieved literature listed above; a high faithfulness score means the answer matches its sources, not that the sources are correct._