(A) Low-power photomicrograph showing tall duodenal villi and lamina propria with lymphoplasmacytic infiltration. (B) The submucosa showing deposition of periodic acid-Schiff (PAS) negative acellular material in the blood vessel wall (PAS, ×100). (C) The acellular material in the vessel wall showing congophilic and apple-green birefringence on polarization (Congo red, ×200). (D) Positive result for serum amyloid A protein immunohistochemistry staining in the blood vessel wall (immunoperoxidase, ×100).