Narrative Review on Chronic Endometritis and Its Diagnosis in the Reproductive Process: Focus on Possible Future Diagnostic Perspectives

(1) Background: Chronic endometritis (CE) is a chronic disease of the endometrium characterized by inflammatory infiltration into the endometrial stroma. The diagnosis of CE is complex. Clinical examination and transvaginal ultrasound are not specific for CE. Biopsy is an indispensable tool. Two specific populations can be analyzed at the endometrial level: CD138 positive plasma cells and CD56 positive Natural Killer cells. (2) Methods: Our narrative review was based on an online search with a focus on the last ten years of literature in the English language. (3) Results: Twenty studies on CD138 positive plasma cells and 16 articles on CD56 positive Natural Killer cells highlighted the correlations of CE with diagnostic possibilities and reproductive outcomes. (4) Conclusions: The etiological pathway and management of CE require further scientific studies and investigations. Hysteroscopy is the diagnostic gold standard, but other blind biopsy techniques (i.e., Perma, Pipelle, Novak, etc.) and molecular procedures may help in the diagnosis of chronic endometritis.