General
- These are lymphomas confined to the Central Nervous System (CNS) at presentation.
- No association with immunodeficiency
- They correspond histologically to systemic low-grade B-cell lymphomas, typically extranodal marginal zone lymphoma, small lymphocytic lymphoma, lymphoplasmacytic lymphoma, or low-grade B-cell lymphoma NOS.
Definition
- Essential
- Biopsy showing a lymphoma confined to the CNS at presentation that corresponds histologically to one of the types of systemic low-grade B-cell lymphoma.
- Desirable
- Detection of B-cell clonality by PCR.
Numbers
- 3% of all CNS lymphomas
- Majority are of B-cell lineage
- Exclusively affect adults (median age 49 years).
WHO Grade
- The tumour is described as a low-grade B-cell lymphoma.
- A specific numerical CNS WHO grade (1–4) is not provided in the classification.
Histopathology Features
Microscopic
- Composed of small lymphocytes and marginal zone cells.
- Often show plasmacytic differentiation.
- Cells typically form perivascular cuffs of small, monomorphic-appearing lymphoid cells.
- The proliferation index (Ki-67) is characteristically low (<10%).
Macroscopic
- Limited specific data are available.
Immunophenotype
- Neoplastic cells are typically positive for B-cell markers (CD20, CD79).
- They are typically negative for CD3, CD5, CD10, CD23, BCL6, cyclic D1, TdT, and EBV-encoded small RNA (EBER-)
- Cells are usually BCL2+, and are IRF4 (MUM1)+/-
Pathogenesis
- Clonal rearrangement of the IGH and/or IGK genes has been reported.
- Rarely, cases show loss of heterozygosity on 6q (including the TNFAIP3 locus) or MALT1 rearrangement.
- MYD88 p.L265P and translocations involving IGH, BCL2, or CCND1 were typically found to be absent in evaluated cases.
Clinical Features
- Headache, seizures, and speech impairment, can be present for months or years prior to diagnosis.
Radiological Features
- Lesions may appear well defined or infiltrative.
- They occur as a solitary lesion or multiple discrete lesions, or as diffuse involvement of the white matter of the brain.
- They are primarily supratentorial, affecting the cerebral cortex lobes or basal ganglia, but can involve the cerebellum, spinal cord, leptomeninges, and choroid plexus.
Management
- Treatment typically involves resection, steroids, radiation, and/or chemotherapy.
- Staging includes lumbar puncture, bone marrow biopsy, and imaging to exclude extracranial disease.
Prognosis
- The course is generally less aggressive with a better prognosis compared to primary diffuse large B-cell lymphomas of the CNS.
- Most patients are alive with stable disease or are disease-free.
Differential diagnosis
- Glioma
- Intravascular lymphoma
- Demyelinating disease.
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