Endometrial tissue in myometrial vessels not associated with menstruation

The presence of endometrial tissue in myometrial vessels has been described in the literature primarily in association with the menstrual period. We reviewed 277 hysterectomy specimens to assess the frequency of endometrial tissue in myometrial vessels in the uteri of nonmenstruating women. Intravascular endometrial tissue was observed in 14 cases, all of which showed extensive adenomyosis usually present in multiple foci. None of the uteri without adenomyosis showed intravascular endometrial tissue. In foci of adenomyosis, the intimate relationship of endometrial tissue and vessels might be explained by the possible origin of endometrial tissue from uncommitted perivascular cells, a possibility that is supported by our failure to demonstrate a connection between the foci of adenomyosis and endometrium in serial sections. When the uncommitted perivascular cells proliferate, they may impinge on endothelially intact vascular lumina and later become intraluminal. Pathologists should be aware of this phenomenon associated with adenomyosis to avoid interpreting the cells within vessels as being neoplastic.