Brain Pathology Case of the Month - September 2014

Contributed by Ross A. Okimoto, MD1; Arie Perry, MD2; James L. Rubenstein, MD, PhD1
1 Division of Hematology/Oncology, University of California, San Francisco, San Francisco, CA.
2 Department of Neuropathology, University of California, San Francisco, San Francisco, CA.


A 77-year-old female presented with three months of headache, impulsivity, irritability and aggressive behavior. Neurological exam revealed a flattened affect, poor short-term memory and urinary incontinence.

Magnetic Resonance Imaging (MRI) revealed an extra-axial mass that extended over the convexities of the bilateral frontal lobes and invaded the superior sagittal sinus and the overlying calvarial diploic space (Figures 1, 2, 3 and 4). The lesion infiltrated into the sub-adjacent bilateral frontal lobe cortex and demonstrated homogenous contrast enhancement on T1-weighted images (Figures 1 and 2) and hyperintense signal on T2-weighted images (Figures 3 and 4). The patient underwent a bifrontal craniotomy that revealed a lesion which adhere to the undersurface of the bone flap. The left and right frontal lobe dura were opened and revealed an invasive lesion with an ill-defined brain-tumor interface. A subtotal resection was performed and multiple white-tan tissue fragments were submitted for pathological evaluation.


Microscopic examination demonstrated dural involvement by a dense cellular infiltrate, composed mainly of mature small lymphocytes and monocytoid cells with a low mitotic index. The lymphoid cells appeared in diffuse sheets with focal vague suggestions of follicular/nodular architecture (Figures 5 and 6). Immunoperoxidase stains showed that the vast majority of mature small lymphocytes were positive for CD20 (Figure 7). Stains for T-cell markers CD3, CD5, and CD43 highlighted only a minority population of admixed small lymphocytes consistent with reactive T-cells with no co-expression of either CD5 (Figure 8) or CD43 by the dominant B-cell population. Stains for CD21 and CD23 highlighted scattered rounded aggregates of follicular dendritic cells, consistent with benign B-cell follicles that have been colonized by the neoplastic B-cell population. In addition, there were larger, more ill defined, and more elaborate meshworks of dendritic cells underlying the neoplastic B cells in other areas, which corresponded to the follicular areas in the H&E stain. The dominant B-cell population was negative for CD10, CD23, BCL-1 (cyclin D1), and BCL-6. Additionally, immunohistochemistry for IgG highlighted numerous plasma cells, while the IgG4 was negative. Flow cytometry demonstrated a lambda-restricted B-cell lymphoid population lacking expression of CD5, CD10, and CD23. What is the diagnosis?


International Society of Neuropathology