The patient went on to have an open dural biopsy. 

Histology:

Sections show small fragments of a densely cellular tumor composed of solid sheets of small to medium-sized lymphocytes. The tumor cells contain round nuclei with fine granular chromatin and inconspicuous nucleoli. No follicles or germinal centers are seen. No granulomas are identified.

Immunohistochemical results show a predominantly CD20+/CD79a+/CD5+/BCL2+ B-cell tumor cell population with negative staining for CD10, CD23, CD138, CD43, BCL6 and CyclinD1. The tumor cells demonstrate kappa-ISH light chain restriction. There is a background population of CD3 positive T-cells. The Ki67 proliferation index is approximately 10%.

FINAL DIAGNOSIS: Low-grade B-cell non-Hodgkin lymphoma.

Comment: The histological and immunohistochemical features are those of a low grade CD5+ B-cell non-Hodgkin lymphoma, favoring chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL).