**5. Histological diagnosis**

The histological diagnosis of chronic endometritis is based on the presence of a number of criteria that have been widely described in the literature: superficial stromal edema, increased stromal density, and inflammatory stromal infiltration, which is predominated by the presence of lymphocytes and plasma cells [32]. The presence of the latter is considered by some authors as a marker specific to endometritis; according to some, in particular, the presence of a few or even a single stromal level plasma cell is enough to settle the diagno‐ sis on chronic endometritis [33].

However, the majority of authors agree upon a greater importance that an overall view of all histological aspects be established (the coexisting presence of several criteria suggestive of chronic endometritis—rather than focusing on a single diagnostic criterion).

An unusual distribution pattern of leukocytes in the endometrial mass and the presence of an increased number of B lymphocytes may contribute to the diagnosis because the B lympho‐ cytes in the endometrium normally make up less than 1% of the leukocyte count.
