The evaluation of patients with mid-facial destructive lesions includes imaging studies to delineate the extent of disease, as well as biopsy for immunohistochemical studies, flow cytometry, and identification of molecular studies. Extranodal tumors are difficult to diagnose and can be confused with reactive processes. There is no one specific diagnostic test; nasal NK/T-cell lymphoma diagnosis is based on a combination of clinical, histologic, immunophenotypic, and genotypic features. Clinical features that help the diagnosis include the location (nasal area), pattern of disease in extranodal sites, and rarity of nodal disease. Immunophenotyping may not be specific, but to be considered a nasal NK/T-cell tumor it must include NK-cells and/or cytotoxic T-cell-associated antigens. The most common cell phenotype is CD2+, cytoplasmic CD3+, surface CD3-, and CD56+. Absence of EBV by in situ hybridization helps to rule out nasal NK/T-cell lymphoma. Histology shows necrosis in essentially all cases, and, although common, angiocentric infiltrates are not required for the diagnosis (37).

The differential diagnosis includes LYG, an NK-cell lymphoproliferative disorder also referred to as NK-cell large granular lymphocytosis, herpes simplex infection (HIS), enteropathy-associated T-cell lymphoma (ETCL), WG, and cocaine abuse. HIS may stimulate reactive lymphoid proliferation that, in the nasal area, can mimic nasal NK/T-cell lymphoma. LYG shows many overlapping features, but is a B-cell disorder. ETCL usually involves the GI tract, and may result in extensive necrosis, but only rarely is associated with EBV (37).

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