Diagnostic Pitfalls in "Low-Grade Lymphoma" of the Orbit and Lacrimal Gland.

AIMS: To investigate potential diagnostic pitfalls associated with the identification of low grade lymphoma in the orbit and lacrimal gland region.

METHODS: To systemically review all cases diagnosed as low grade lymphoma of orbit and lacrimal gland within a 2 year period at a specialist ophthalmic centre. To ascertain the frequency of diagnostic errors in this group of cases, in particular to look for known pitfalls associated with follicular colonisation by marginal zone lymphoma and the recently identified atypical variant of follicular lymphoma (FL). A series of 21 cases were reviewed.

RESULTS: We identified two diagnostic errors; one case of extra nodal marginal zone lymphoma (ENMZL) which showed follicular colonisation and was misinterpreted as a FL and a case of missed mantle cell lymphoma (MCL). We identified no cases of atypical FL.

CONCLUSION: Within the orbit and lacrimal gland the term "low grade lymphoma" encompasses the following types of lymphoma: ENMZL, FL, MCL and chronic lymphocytic leukaemia/small lymphocytic lymphoma (CLL/SLL). The typical and atypical immunophenotype of these entities is discussed. The diagnosis of ENMZL, by far the most common low grade lymphoma to occur in these areas, is to some extent a difficult diagnosis and is often one of exclusion. The pitfalls of follicular colonisation and the concept of atypical follicular lymphoma are discussed.