Histochemical and immunohistochemical characterization of foamy histiocytes (muciphages and xanthelasma) of the rectum

Despite being relatively common in the rectum, foamy histiocytes have recei ved scant attention as to the antecedent lesion that causes them to form or their histologic characterization on the types of muco-substances they acc umulate. One-hundred consecutive tissue sections of the rectum from an equa l number of patients were reviewed for the presence of foamy histiocytes, e valuated for their associated histologic features, and examined histochemic ally for five types of mucin. Immunohistochemical and electron microscopic studies were performed. Forty (40%) of the rectal biopsy tissues contained foamy histiocytes. Patients presented with diarrhea, hematochezia, intestin al habit change, constipation, hemorrhoids, and abdominal pain. Endoscopica lly, 19 patients were thought to have rectal nodules or polyps. Histologica lly, 25 of the patients had regenerative changes in the adjacent mucosa and 14 had hyperplastic changes. In 36 patients (90%), the foamy histiocytes w ere located superficially in the lamina propria. Associated changes indicat ed that they are found in areas that are subject to an injury that is in a healing phase. These changes included mild fibrosis and chronic inflammatio n of lamina propria with mild architectural distortion. Thirty-five (88%) c ases showed staining for D-PAS, Alcian blue stain pH 2.5, and the cocktail Alcian blue stain/PAS. Mucicarmine was positive in 25 (63%) cases. The Alci an blue stain pH 1.0 was positive in 19 (59%) of 32 cases. Ultrastructural studies showed electron-dense globules, Two cases were histologically ident ical to the other 38 but they did not stain for any mucin. Ultrastructural features disclosed clear vacuoles and thus represent a xanthelasma of the r ectum. The foamy cells in all cases were confirmed to be histiocytes by imm unohistochemistry and electron microscopy. Although muciphages and xanthela sma of the rectum may mimic polyps endoscopically, they are not related to any specific symptom or clinical finding, despite the fact that they probab ly represent remnants of a previous injury. Muciphages contain neutral, wea kly acidic or strongly acidic mucin. The main type of acidic mucin is sialo mucin with a smaller component of sulfated mucin.