Focal Glandular Inflammation of the Endometrium (So-called Focal Necrotizing Endometritis): Clinicopathologic and Immunohistochemical Study of 13 Cases

Focal necrotizing endometritis (FNE) is a rare phenomenon consisting of localized periglandular and intraglandular inflammation with luminal accumulation, epithelial cell necrosis, and absence of plasma cells. Since its initial morphologic description, FNE has not been further studied. We document clinical correlates, morphology, and immunophenotype of glandular (using PAX2, PTEN, Β-catenin, MSH6, and PMS2) and inflammatory (using CD3, CD20, CD4, CD8, and CD138) populations in 13 cases of FNE identified over a 4-yr period, representing 0.5% of all endometrial biopsies surveyed. Immunohistochemistry for CD3, CD20, CD4, CD8, CD138, PAX2, PTEN, B-catenin, MSH6, and PMS2 was used to characterize cellular components. The mean patient age was 43 (range: 31–61), and body mass index was 32 (range: 23–54). Biopsy was performed for infertility/recurrent pregnancy loss (n=7), abnormal uterine bleeding (n=5), or postmenopausal bleeding (n=1). In all biopsies, the process was confined to <8 glands. The infiltrate was T-cell predominant in 11/13 cases; in 2 cases, there was similar density of CD20- and CD3-positive cells. In all cases, CD8-positive T cells predominated over CD4-positive cells. CD138 was negative in all FNE areas. Affected glands showed normal nuclear PMS2, MSH6, and PAX2, as well as membranous Β-catenin, in all cases. PTEN consistently showed reduced staining, but no definitive loss compared with uninvolved glands. Three patients received doxycycline. Follow-up biopsies were available for 7 patients, with only one showing persistent FNE. Subsequent pregnancy was achieved in 4/7 patients with FNE and infertility. FNE is an uncommon phenomenon characterized by focal gland involvement by a predominant cytotoxic T-cell population, likely in response to cell damage. The lesion tends not to recur and does not appear to be associated with adverse pregnancy outcomes. A nonaberrant profile of PTEN, PAX2, MSH6, PMS2, and Β-catenin argues against FNE representing a response to early endometrioid neoplasia. Pathologists need to be aware of the occurrence of FNE and distinguish it from clinically actionable inflammation, namely chronic endometritis.