Detection of Epstein–Barr virus-infected lymphoid cells in nasal mucosa or nasopharynx: appearances can be deceptive

The cytomorphological spectrum of extranodal NK/T cell lymphoma (ENKL), nasal type (nasal ENKL), is very broad. In some cases, the morphological findings are so subtle that the possibility of nasal ENKL is easily overlooked. The present study was undertaken to find overlooked or indolent cases of nasal ENKL in the nasal mucosa or nasopharynx of patients who underwent surgical resection of lesions in the nasal cavity because of nasal obstruction or a nasal polyp. We retrospectively reviewed H & E slides of 1,176 patients and selected 40 cases with predominantly small lymphoid infiltrations admixed with other inflammatory cells, presenting a diagnostic challenge and thus requiring further studies. By Epstein–Barr virus (EBV) in situ hybridization performed on 40 selected cases, we identified three cases (7.5 %) with EBV + lymphoid cells (EPLs). All three were pediatric patients. The number of EPL in each lesion ranged from 4 to more than 200 per high power field. By double immunohistochemistry, EPLs were identified as B lymphocytes in two of these cases. We added a recently encountered case in an adult man in which EPLs were T lymphocytes. The presence of EPLs in the nasal or nasopharyngeal mucosa should not be interpreted as ENKL especially in pediatric patients, because de novo nasal ENKL is very rare in childhood and EPLs are mainly B lymphocytes.