Paratrabecular nodules are characteristic and virtually diagnostic of involvement
Diagnostic of involvement if there is a prior diagnosis of follicular lymphoma
If no prior diagnosis we consider this to be highly suggestive
Node biopsy, immunologic study or genetic analysis are necessary to make a definitive diagnosis
Architecture frequently more useful than cytology for grade 1 cases
Typically increased reticulin fibers present
Diffuse infiltrates may also occur
Non-paratrabecular nodules
Typically non-neoplastic unless extensive or cytologically clearly atypical
Uniform population of cleaved cells is indicative of lymphoma
Light chain restriction is indicative of lymphoma
Immunohistochemistry infrequently useful in our experience
Flow staining may be useful if sufficient cells present
Grade 1 follicular lymphoma in marrow in a patient with grade 3 follicular lymphoma in nodes indicates a composite lymphoma
Grade 1 follicular lymphoma in marrow in a patient with diffuse large B cell lymphoma suggests that the large cell lymphoma is derived by transformation of the follicular lymphoma
