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Mucosa-Associated Lymphoid Tissue of the Thymus
Hyperplasia vs Lymphoma

Marie Parrens MD, Pierre Dubus MD, PhD, Marie Danjoux MD, Jacques Jougon MD, Pierre Brousset MD, PhD, Jean-François Velly MD, Antoine de Mascarel MD, Jean P. Merlio MD, PhD
DOI: http://dx.doi.org/10.1309/G3AC-P7K8-2JNK-8C3U 51-56 First published online: 1 January 2002


In the thymus, the relationship between lymphofollicular hyperplasia and mucosa-associated lymphoid tissue (MALT)-type lymphoma is uncertain. We analyzed 14 cases with a diagnosis of thymic follicular hyperplasia in patients with connective tissue disease (n = 2), myasthenia gravis (n = 11), or both (n = 1). In 11 cases, well-defined reactive lymphoid follicles were surrounded by a continuous layer of medullary epithelial cells. A polyclonal rearrangement of the immunoglobulin heavy chain gene (IgH) was observed. In 3 cases, ill-defined lymphoid follicles with sheets of centrocytic-like B cells disrupting the medullary cytokeratin epithelial network were observed on certain sections. These cells expressed the phenotypic features of memory B cells with CD20, CD79a, and bcl-2 positivity and CD5, CD10, CD23, and bcl-6 negativity, and a monoclonal rearrangement of the IgH gene was detected.

Appropriate sampling, cytokeratin staining, and molecular analyses may help to identify early MALT-type lymphoma developing in the setting of thymic lymphofollicular hyperplasia.

Key Words:
  • Thymus
  • Mucosa-associated lymphoid tissue
  • MALT-type lymphoma
  • Extranodal marginal zone B-cell lymphoma
  • Thymic follicular hyperplasia