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Slide 36 of 70
|Slide 36. Transmural Lymphoid Aggregates |
|It is perhaps unfair that the single pathognomonic feature of Crohn’s disease is not demonstrable as such in the mucosal biopsy. Classic Crohn’s disease is characterized by nodular lymphoid aggregates that are focally coalescent, and more importantly, transmural in affected segments. More precisely, these transmural lymphoid infiltrates are essentially diagnostic of this disorder when they occur in sites not affected by deep or fissuring ulcers. The submucosa is typically expanded by these aggregates, together with the attendant features of ongoing acute and chronic inflammation with fibrosis. Although transmural inflammation cannot be discerned in biopsy samples, careful examination of submucosal tissues, when present, may still be rewarding. In ulcerative colitis, inflammation of the superficial submucosa, often beneath thickened muscularis mucosae, is generally sparse and diffuse. In contrast, nodular infiltrates may be discerned in the superficial submucosa in Crohn’s disease. Exudative debris or ulcer extending into the biopsy base may be a possible mucosal biopsy correlate of deep or fissuring ulcers, a finding that also favors a diagnosis of Crohn’s disease. |