Cytoskeletal immunohistochemistry of central neurocytomas.

Central neurocytomas are rare intraventricular tumors. Patients with such tumors have a favorable prognosis after surgical removal. These tumors may be misdiagnosed as neuroblastomas or gliomas, risking the complications of adjuvant therapy. Diagnosis of central neurocytoma requires that the tumor shows the ultrastructural features of mature neuronal differentiation, including the presence of synapses and dense-core and clear vesicles in addition to profiles of neuritic processes with microtubules. The cytoskeletal phenotype of central neurocytomas has not been previously characterized, but it may facilitate their definitive recognition when ultrastructural examination is not possible. Ten central neurocytomas were examined by immunohistochemistry for phosphorylation-dependent/independent neurofilament epitopes, neuron-associated class III beta-tubulin, microtubule-associated proteins (MAP2, tau), and glial fibrillary acidic protein (GFAP). The neuronal nature of all neoplasms was documented by immunoreactivity for synaptophysin in nine tumors and for phosphorylation-independent neurofilament-H/M in the remaining case. Electron microscopy in four cases showed synapses and dense core vesicles. All tumors were immunoreactive for class III beta-tubulin and MAP2, which were seen in cytoskeletal structures by immunoelectron microscopy. Two thirds of the cases were immunohistochemically positive for neurofilament epitopes. None of the tumor cells displayed GFAP immunoreactivity, although reactive astrocytes were present. These data suggest that central neurocytomas may be recognized by synaptophysin immunoreactivity and that the expression of cytoskeletal epitopes indicates that these tumors are well-differentiated neuronal neoplasms.