Eosinophilic metaplastic atypia in exfoliated cells of ovarian endometriosis: a potential cytodiagnostic pitfall in peritoneal fluids

Endometriosis is a protean clinical condition that is defined pathologically by the presence of endometrial glands and stroma with associated evidence of bleeding occurring outside of the usual anatomy of the endometrium/uterine cavity. It is one of the most common benign gynecologic disorders, affecting approximately 5% of all women. The prevalence of the condition may increase to as high as 30% in infertile premenopausal women. Despite extensive study, the etiology of this condition remains an enigma. Cytopathologists may encounter abnormal cells arising from endometriosis in cervicovaginal cytology samples, nongynecologic exfoliative cytology cases, needle aspiration biopsy slides, and in histologic materials and cell blocks. We report a case of eosinophilic epithelial metaplasia present in cytospins made from a peritoneal washing taken from a perimemopausal woman. This patient was concomitantly histologically documented to have ovarian surface endometriosis with similar metaplastic alteration. The case highlights the potential for misdiagnosis of such processes as being potentially malignant and stresses the need for cytohistologic correlation whenever possible.