Heterotopic bone formation in the gastrointestinal tract.

Heterotopic bone is found rarely in the gastrointestinal tract. Here we report four cases, one of which occurred in Barrett's esophagus in an area of metaplasia of specialized cell type without evidence of neoplasia. In the remaining cases, bone was associated with mucin-producing tumors of the appendix, transverse colon, and rectum. The clinical and pathologic findings are discussed in detail. Heterotopic bone formation in the digestive tract usually occurs in the colorectum in association with benign or malignant epithelial tumors, and most often with those that produce abundant mucin. The pathogenesis of the osseous metaplasia in the gastrointestinal tract is not understood, although mucin extravasation is an almost constant feature. Fragments of metaplastic bone in a biopsy of a mucinous neoplasm of the digestive tract should not be misinterpreted as osseous invasion.