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.