Atypical lymphadenopathies of the head and neck.

Atypical lymphadenopathies fail to achieve the morphologic criteria of a malignant neoplasm, but exceed the usual concepts of follicular, lymphoid, or sinus histiocytic hyperplasias. Rich cellular proliferations usually composed of prominent histiocytes, or immunoblasts, or both with or without a vascular scaffolding obscure the nodal architecture. Toxoplasmosis, infectious mononucleosis, zoster, and vaccination-induced lymphadenopathies are caused by infectious agents, dermatopathic lymphadenitis is associated with cutaneous disease, anticonvulsant pseudolymphoma occurs in individuals hypersensitive to anticonvulsants (usually phenytoin), and Chediak-Higashi syndrome is an inherited abnormality of lysosomal microtubule function; the causes of sinus histiocytosis with massive lymphadenopathy, giant lymph node hyperplasia, angioimmunoblastic lymphadenopathy, mucocutaneous lymph node syndrome, and this histiocytoses remain unknown. The clinical course of these abnormalities varies from self-limited acute diseases (viral lymphadenopathies, toxoplasmosis, dermatopathic lymphadenitis, and usually anticonvulsive lymphadenopathy) to protracted, but benign abnormalities (sinus histiocytes with massive lymphadenopathy, giant lymph node hyperplasia, and multifocal eosinophilic granuloma). The diagnosis of angioimmunoblastic lymphadenopathy, Chediak-Higashi syndrome, and mucocutaneous lymph node syndrome necessitates a guarded prognosis, for death or the advent of a malignant lymphoma may interrupt their clinical course. Acute disseminated histiocytosis, even though the proliferated cell lacks the cytologic criteria of malignancy, should be regarded and treated as a malignant neoplasm.