Nodular Histiocytic Aggregates in the Endometrium: A Report of 7 Cases

Nodular aggregates of nonfoamy histiocytes in the endometrium are uncommon. We describe herein the clinical and pathologic characteristics of 7 additional cases in endometrial biopsies or curettages. The patients ranged in age from 48 to 72 years, and the most common presenting symptom was abnormal uterine bleeding. Five of seven patients had undergone prior endometrial sampling (including 1 who had undergone 3 endometrial biopsies over the preceding 5 yr for follow-up of abnormal uterine bleeding). In 2 cases, an endometrial polyp was present in the same sample, and an additional 2 were found to have endometrial polyps on subsequent biopsies that were performed within 4 months of original samplings. The lesions, which ranged in size from 1 to 8 mm, were composed of monomorphic cells with abundant pink eosinophilic cytoplasm with a vaguely nodular arrangement. Two cases showed focally high mitotic activity with up to 4 mitoses per high-power field. Patient outcomes were unremarkable, which affirms the benign nature of the proliferation. Several features of this lesion, including mitotic activity, focal necrosis, and tight aggregation of cells, may raise the possibility of a neoplastic proliferation. This differential diagnosis can be readily resolved by awareness of the lesion and immunohistochemical analyses. Possible pathogenetic considerations are discussed, but these nodules represent, in our opinion, reaction to necrotic tissue in the endometrial cavity, possibly related to prior procedure.