2.2 Histopathologic and Immunohistochemistry findings
Multifocally, the spinal nerve roots and epidural surface of the dural mater of the meninges were surrounded or covered by plaques of neoplastic round cells which infiltrated the adipose tissue surrounding the spinal tissues. The neoplastic infiltrates were composed of sheets of large round cells with small amounts of eosinophilic cytoplasm with distinct cell borders. Their nuclei were large and round to occasionally indented with finely stippled to coarsely granular to open (marginated) chromatin and often with a single prominent nucleolus. The mitotic index was moderate to high (5 to 12 mitotic figures per HPF) with moderate anisocytosis and anisokaryosis. The areas of neoplastic infiltration often were congested with areas of hemorrhage. The neoplasm formed a plaque-like band over the dura mater overlying the cranial aspect of the spinal cord, multifocally surrounded the spinal nerve roots in the lumbosacral area and infiltrated the adipose tissue surrounding the cauda equina. The perivascular spaces within the spinal cord were often expanded by edema and the myelin sheaths surrounding spinal axons were also multifocally expanded by clear space presumed to be edema. The kidneys were infiltrated by clusters of moderate to large numbers of atypical round cells similar to those observed in the spinal meningeal tissues. Infiltrates of similar atypical round cells were also present multifocally in the lungs, liver, testes and one lymph node.
Immunohistochemical staining of a sample from the meninges found the majority of cells in the round cell infiltrates exhibited moderate to intense cytoplasmic/membranous immunoreactivity for CD20, including a few mitotic figures. Very small numbers of individually scattered round cells exhibited moderate to intense cytoplasmic/membranous immunoreactivity for CD3.