Osseous metaplasia is a rare condition in which there is a transformation of the
normal endometrial tissue into bone. It is an uncommon clinical finding with an
incidence of 0,3/1000 and most cases occur after miscarriage or abortion. The
presence of bone in the endometrium was first described by Virchow who related this
condition to a spontaneous differentiation of fibroblasts into osteoblasts. Typically, this
type of metaplasia occurs during reproductive years and more than 80% of reported
cases ocurr after pregnancy.
There are two main theories to explain the existence of bone fragments in the
endometrial tissue. The one by Thaler, who relate this entity to retention of osseous
fetal parts after abortion or miscarriage after 12 weeks of pregnancy. This first theory
cannot explain cases that occurr in patients without previous pregnancies. The second
theory is that of a true endometrial osseous metaplasia, in which there is a osseus
transformation of the endometrial stromal cells, this metaplasia is consequence of
irritative, toxic or hormonal stimuli. Probably both theories are right, with cases of true
metaplasia and cases in which retained bones, causes an endometrial inflammation
which leads to a secondary osseous metaplasia.