SENTINEL LESIONS OF PRIMARY CNS LYMPHOMA

Some patients ultimately diagnosed with primary CNS lymphoma (PCNSL) h ave transient symptomatic contrast enhancing lesions. These ''sentinel lesions'' of PCNSL recede spontaneously or with corticosteroid treatm ent and present an important diagnostic dilemma because they show vari able, but non-diagnostic histopathological features. Four previously h ealthy, immunocompetent patients aged 49 to 58 years had contrast enha ncing intraparenchymal brain lesions. Before biopsy, three of the four were treated with corticosteroids. Initial biopsies showed demyelinat ion with axonal sparing in two, non-specific inflammation in one, and normal brain in one. Infiltrating lymphocytes predominantly expressed T cell markers with rare B cells. All four patients recovered within t wo to four weeks after the initial biopsy and imaging studies showed r esolution of the lesions. The CSF was normal in three of the four pati ents tested; oligoclonal bands were absent in both of the two tested. After seven to 11 months, each patient developed new symptomatic lesio ns in a different region of the brain, biopsy of which showed a B cell PCNSL. The mechanism of spontaneous involution of sentinal lesions is not understood, but may represent host immunity against the tumour. S entinel lesions of PCNSL should be considered in patients with contras t enhancing focal parenchymal lesions that show non-specific or demyel inative histopathological changes. Close clinical and radiographic fol low up is essential if PCNSL is to be diagnosed early in such patients .