Primary CD30/Ki-1 positive anaplastic large cell lymphoma of the central nervous system occurring in a patient with a seventeen-year history of essential thrombocythemia.

We present a rare case of central nervous system lymphoma that occurred in a patient who had essential thrombocythemia for 17 years. MRI examinations disclosed multiple ring-enhanced lesions that had shown bilateral spreading in the different period. Pathological examinations confirmed CD30/Ki-1-positive ALK negative anaplastic large cell lymphoma. The possible pathogenic mechanisms of this disease are discussed.