Heterotopic ossification in appendiceal mucinous neoplasms: clinicopathological characteristics of 3 cases.

Heterotopic bone formation is a very rare event in the gastrointestinal tract including in the appendix. Here we report three cases of heterotopic ossification in appendiceal mucinous neoplasms, one occurring in an appendiceal mucinous cystadenoma, another in a low-grade appendiceal mucinous neoplasm, and the third occurring in an appendiceal mucinous adenocarcinoma. The clinicopathologic characteristics of these three present cases and two previously reported cases are discussed in detail. The mechanism of heterotopic ossification in appendiceal mucinous neoplasm is still unclear, but mucin extravasation and subsequent calcification may be predisposing events.