Secondary central nervous system involvement by follicular lymphoma: case report and review of the literature

BACKGROUND: We report a patient with indolent stage IV follicular lymphoma, grade 1, initially successfully treated with chemotherapy, who later developed aggressive diffuse large B-cell lymphoma in the parieto-occipital lobe 8 years after initial presentation. The differing patterns of lymphomatous involvement of the central nervous system (CNS) are briefly reviewed, with a focus on the patterns seen in secondary CNS spread by low-grade lymphomas. CASE DESCRIPTION: A 53-year-old man was diagnosed with stage IV follicular lymphoma, grade 1, in 1996. Although initial chemotherapy was successful, he developed several recurrences of lymphoma over the following years. In May 2004, he presented with a discrete, single, massive parieto-occipital lobe brain lesion. The mass failed to regress with empiric cranial external beam radiotherapy. Because of suspicion of an unusual infection, the lesion was surgically excised in its entirety. The mass proved to be an aggressive diffuse large B-cell lymphoma, transformed from his previous follicular cell lymphoma, with retention of strong Bcl-2 and Bcl-6 immunoreactivity. CONCLUSIONS: Parenchymal brain involvement, as opposed to dural or leptomeningeal, is a relatively uncommon pattern of spread to the CNS for systemic lymphomas. More significantly, follicular lymphomas are one of the least frequent types of indolent lymphomas to develop clinically apparent, secondary CNS spread. The presentation of an indolent follicular lymphoma with transformation to an aggressive diffuse large B-cell lymphoma within the brain parenchyma is rare. Its manifestation as a massive, singular lesion is unique and prompted diagnostic confusion.