lymphoid aggregates


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  • Ddx

    • normal
      • common in elderly
    • benign
      • monoclonal B cell lymphocytosis
      • autoimmune: RA, SLE, AIHA, ITP, Hashimoto
      • aplastic anemia
      • viral: HIV, hepatitis
      • MPN, MDS
    • lymphoma

  • Benign histology

    • architecture: single, small, well circumscribed, nontrabecular, random distribution
    • morphology: polymorphous (has plasma cells, histiocytes), normal cytology
    • immunophenotype: predominantly T cells or mixed T and B. CD10 negative. BCL2 negative in GCs. Lack aberrant immunophenotype.
    • molecular: lacks IGH or TCR rearrangement

  • Lymphoma histology

    • architecture: multiple, large, infiltrative, paratrabecular, intrasinusoidal
    • morphology: monomorphic
      • polymorphic tend to be peripheral T lymphoma, Hodgkin lymphoma
    • immunophenotype
      • B lymphoma: predominantly B cells, aberrant CD5, BCL2 in GCs, CD10+ in 1/2 of FL
      • B lymphoma with plasmacytic differentiation: atypical lymphoid cells + monotypic plasma cells = MZL, LPL
      • T lymphoma: aberrant T cells, aberrant loss of pan T antigens, TCR rearrangement

  • Pearls

    • use PAX5 or CD79a for B cells in pt treated with anti-CD20 therapy
    • G-CSF causes sheets of paratrabecular promyelocytes, mimicks large cell lymphoma
    • reactive GCs usually seen in autoimmune dz, but also can be splenic MZL
    • paratrabecular: almost always neoplastic, usually FL
    • intrasinusoidal: usually neoplastic: intravascular large B cell, splenic MZL, splenic diffuse red pulp small B lymphoma
    • cyclin D1 = MCL
    • ALK1 = anaplastic large cell
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