Uterine intravascular menstrual endometrium simulating malignancy

Intravascular menstrual endometrium, a rare finding in hysterectomy specimens, can pose clinically critical differential diagnostic problems. We describe a 28-year-old female with cervical dysplasia and numerous foci of menstrual endometrium in the parametrial blood vessels of her subsequent hysterectomy specimen. Histologically, the intravascular tissue consisted of small spindled stromal cells, larger cuboidal epithelial cells, or both components in close association. Immunohistochemically, the small spindled cells were vimentin positive and the larger cuboidal cells stained with epithelial markers. Distinction of intravascular menstrual endometrium from intravascular malignancies such as carcinoma, sarcoma, or lymphoma may be difficult, especially at the time of frozen-section diagnosis. Awareness of this process, attention to its cytologically bland, usually biphasic appearance, knowledge of the menstrual status, and application of appropriate immunohistochemical markers will allow distinction from neoplasia.