NIMG-56. THE RARE CASE OF PRIMARY DURAL BASED MARGINAL ZONE B-CELL LYMPHOMA CAMOUFLAGING AS MILD FOCAL DURA THICKNESS AND PACYMENINGEAL ENHANCEMENT

INTRODUCTION Primary Dural Based Marginal Zone B-Cell Lymphoma (MZBCL) is a subtype of PCNSL with an incidence rate ranging from 0.6 to 3% of all brain tumors. MZBCL typically presents as an extra-axial mass resembling meningioma. Here we report an unusual case of MZBCL with initial radiographic findings of mild nonspecific thickening tentorium and pachymeningeal enhancement surrounding 7th and 8th cranial nerves. CASE REPORT A 58-year old woman with clinical history of CMV infection, polyclonal gammopathy and unruptured left ICA aneurysm post coil embolization who presented for an evaluation of mild thickening and enhancement of the left tentorium cerebelli and 7th/8th nerve root complex. Differential considerations included inflammatory/autoimmune conditions (idiopathic hypertrophic pachymeningitis, neurosarcoidosis, Tolosa-Hunt syndrome), infections, structural lesion, benign or malignant neoplasm. Serum studies were normal. Multiple CSF studies were negative. Flow cytometry showed no malignant cells with few small lymphocytes. She was followed with the imaging surveillance for nine months until further increased thickening of dura on MRI. She underwent cerebellar dural biopsy that was consistent with MZBCL composed mainly of small CD20+ B-cells and negative MYD88. PET scan showed no systemic involvement. Bone biopsy revealed no evidence of lymphoma. The focal leptomeningeal enhancement improved significantly after she received four doses of systemic rituximab treatments. DISCUSSION Our case highlights the importance of surveillance and brain biopsy in cases of mild focal dura/pachymeningeal thickness and enhancement if no conclusive diagnosis has been established, as it might be one of the rare tumors such as MZBLC.