Atypical B‐cell infiltrate in a pediatric patient: diagnostic and pathogenetic considerations

Abstract

Pediatric primary central nervous system lymphoma (PCNSL) represents1–1.5% of all PCNSL. Pediatric PCNSL are usually high grade B‐cell lymphoma (30%) or anaplastic large cell lymphomas. Herein we report a 15 year‐old male with a well‐circumscribed, enhancing mass centered on the right thalamus with mass effect on the 3rd ventricle and obstructive hydrocephalus. Endoscopic biopsy produced only hemorrhage; repeat biopsy three months later produced multiple fragments of pink‐tan soft tissue including pineal gland, grey matter, granulation tissue, choroid plexus, and a diffuse mononuclear cell infiltrate composed of a mixture of small round and large atypical lymphoid cells with irregular vesicular nuclei, 2 to 3 nucleoli attached to the nuclear membrane, and moderately abundant eosinophilic cytoplasm. The large lymphoid cells showed immunoreactivity for CD20, PAX‐5, and CD79a (B‐cell markers) but were negative for epithelial and germ cell markers; small T lymphocytes were also present. The lymphocytic process infiltrated brain tissue containing atypical astrocytes and large binucleated neurons. Immunoglobulin heavy chain (Ig‐VDJ; B‐cell) and T‐cell receptor (TCR) beta and gamma gene rearrangement studies showed a monoclonal B‐cell population. This atypical B‐cell infiltrate with features of lymphoma may have arising in an inflammatory infiltrate accompanying a pre‐existing glio‐neuronal tumor.