Primary central nervous system lymphoma without intracranial mass in a child. Diagnosis by documentation of monoclonality.

Primary central nervous system lymphoma is a rare presentation of lymphoma and is usually seen in adults, often in association with immunodeficiency. Evaluation of these patients classically shows discrete intracranial lesions, and long-term prognosis despite treatment is poor. The case of a child is presented who had no identifiable predisposing factors, no radiologic evidence of intracranial mass, no evidence of systemic disease, and in whom the diagnosis of primary CNS lymphoma was made based on documentation of a monoclonal population of malignant B-cells in the cerebrospinal fluid. The patient, in whom irreversible blindness developed, was treated with a combination of cranial radiation, and intrathecal and systemic chemotherapy, and is currently alive and disease-free 15 months after diagnosis.