NIMG-89. CNS-ISOLATED RICHTER’S TRANSFORMATION: THE FALLIBILITY OF NEURO-IMAGING AND THE CRITICAL ROLE OF BRAIN BIOPSY IN A CHALLENGING DIAGNOSIS

Abstract

Abstract INTRODUCTION An 81-year-old male was admitted for acute encephalopathy and failure to thrive. Workup revealed a lymphocyte-predominant leukocytosis, prominent axillary and mediastinal lymphadenopathy on CT, and multiple supra-tentorial FLAIR-hyperintense lesions that were homogenously contrast-enhancing. Axillary lymph node biopsy demonstrated small lymphocytic lymphoma (SLL), a variant of CLL. Despite concern for CNS malignancy, brain biopsy was initially deferred since the patient’s brain lesions were attributed to SLL metastasis. However on hospital day 15, he developed partial seizures, prompting stereotactic biopsy which revealed DLBCL. DATA/DISCUSSION Our case highlights the pitfalls of relying solely upon neuro-imaging to diagnose Richter’s transformation (RT) isolated to the CNS. First, MRI does not differentiate CNS metastasis of systemic lymphoma from CNS RT. A review of 35 biopsy or LP-proven cases of CNS-isolated RT showed imaging characteristics consistent with primary and metastatic CNS lymphoma. When parenchymal lesions are present, all are T2/FLAIR hyper-intense; 60% are unifocal (40% multifocal); and 95% homogenously enhance. Second, CNS-isolated RT is at least 3 times rarer than CNS metastases of CLL. Among patients with CLL, ~1% will eventually exhibit CNS metastasis but < 0.3% will develop CNS-isolated RT. In patients with known CLL and no evidence of high-grade transformation, it is reasonable to attribute brain lesions to CNS metastasis of CLL as opposed to RT, absent a definitive tissue diagnosis. CONCLUSION These data emphasize the importance of biopsy in the workup of CNS lymphoma, especially since treatment differs based on histopathological subtype. Given its chronic indolent course, SLL is typically managed expectantly, whereas the aggressive nature of DLBCL warrants more intensive chemotherapy. Our case also shows that in patients with suspicious CNS lesions, presence of systemic malignancy does not eliminate the need for brain biopsy, and that clinical deterioration should prompt biopsy if not already performed.