choristoma choristoma choristomas, a form of heterotopia, are masses of normal tissues found in abnormal locations. in contrast to a neoplasm or tumor, the growth of a choristoma is normally regulated. it is different from a hamartoma. the two can be differentiated as follows: a hamartoma is disorganized overgrowth of tissues in their normal location (e.g., peutz–jeghers polyps), while a choristoma is normal tissue growth in an abnormal location (e.g., osseous choristoma, gastric tissue located in distal ileum in meckel diverticulum).