Follicular hyperplasia

Author: Mikael Häggström
Follicular hyperplasia is the most common pattern of reactive lymphadenopathy. Reactive follicular hyperplasia is usually associated with varying degrees of paracortical and/or sinus hyperplasia. Older age, increased follicular density (especially back-to-back arrangement) and areas of diffuse nodal effacement leads to a suspicion of follicular lymphoma.

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  Histopathology of reactive follicular hyperplasia

Main differences:

Feature	Follicular hyperplasia of a reactive lymph node	Follicular lymphoma
Density of follicles	Low	High
Follicle distribution	Usually limited to subcortical region	Distributed evenly throughout parenchyma
Follicles extending beyond capsule	Rarely	Often
Follicle sizes and shapes	Uneven	Similar
Cell types in germinal centers	Mixture of cells	Monomorphic or polymorphic
Tingible-body macrophages	Present	Usually rare
Mitotic rate	Usually moderate to high	Usually low to moderate
Mantle zone	Usually distinct	Usually indistinct or absent
Cell polarization	Often seen	Usually absent
Interfollicular areas	Large	Compressed
Areas of nodal effacement	Absent	Occasional

If uncertain, perform the following studies:

Feature	Reactive lymph node	Follicular lymphoma
Bcl-2 in B cells of germinal centers	Negative	Positive (90%)
Light chain restriction on immunostains	Absent (rare exceptions)	Present (20% in paraffin)
Light chain restriction on flow cytometry	Absent restriction (rare exceptions)	Restriction or absent, when gated correctly (95%)
Ig rearrangements	Absent (rare exceptions)	Usually (80%)
t(14;18)	Absent (rare exceptions)	Usually present (90%)

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