Gastric-like (pseudopyloric and pseudofoveolar) metaplasia and Paneth cell hyperplasia-neglected histological features of chronic ileal inflammation.

Architectural distortion and basal plasmacytosis are the most widely recognized histologic features of chronic ileal inflammation. However, these features might be difficult to assess in small, poorly oriented, or superficial biopsies. Additional features of chronic mucosal damage, including pseudopyloric or pseudofoveolar metaplasia and Paneth cell hyperplasia, have been less commonly reported, and their broader appreciation could facilitate the diagnosis of chronic ileal inflammatory conditions. The prevalence of gastric-like (pseudopyloric and pseudofoveolar) metaplasia and Paneth cell hyperplasia was evaluated in 102 ileal biopsies obtained from patients with Crohn's disease (n = 47), ulcerative colitis with endoscopically normal ileum (n = 20) or with backwash ileitis (n = 20), and nonsteroidal anti-inflammatory drugs- (NSAIDs-) induced ileitis (n = 15). Gastric-like metaplasia was identified in 23% of CD and 13% of NSAID-induced ileitis cases, whereas it was absent among all ulcerative colitis cases. Pseudopyloric metaplasia, pseudofoveolar metaplasia, or a combination of both was documented in 13%, 2%, and 9% of Crohn's disease cases, respectively. NSAID-associated cases showed only pseudopyloric metaplasia. Paneth cell hyperplasia was detected in 43% of Crohn's disease cases, 13% of NSAID-induced ileitis cases, and 5% of backwash ileitis cases. Accordingly, pseudofoveolar metaplasia, pseudopyloric metaplasia, and Paneth cell hyperplasia are not uncommon in conditions causing chronic ileal inflammation. They are most frequently detected in Crohn's disease, but may also be present in NSAID-induced ileitis, whereas they are significantly less common in backwash ileitis and absent in normal ileum. Given the surface localization of pseudofoveolar metaplasia, its identification can be particularly helpful when dealing with poorly oriented or superficial samples.