Epstein-Barr virus and a unilateral neck mass.

Although Epstein-Barr infectious mononucleosis (IM) might be considered in the differential diagnosis of multiple neck masses in a young adult, single large masses are not usually associated with IM. This patient did have a solitary mass. Despite lacking other signs of IM, he did have a positive heterophil-agglutination titer and reactive lymphocytes. Other serologic tests can be of value in confirming the diagnosis, especially if the heterophil titer and reactive lymphocytes are absent. These tests are viral capsid antigen IgM and IgG, early antigen, and nuclear antigen. Surgeons should be aware of their usefulness, especially when trying to confirm a difficult diagnosis.