Gliomas of the optic nerve: histological, immunohistochemical (MIB-1 and p53), and MRI analysis

Gliomas of the optic nerve, although typically of pilocytic (WHO grade I) h istology, can present within the spectrum of astrocytic neoplasia including glioblastoma (WHO grade IV). In certain cases, histologic features alone m ake the distinction between pilocytic and diffuse astrocytomas difficult. W e reviewed 22 cases of optic nerve gliomas, 19 of which were pilocytic astr ocytomas (PA), and 3 of which were diffuse, non-pilocytic astrocytomas. The cases were evaluated for their clinical course, radiographic appearance, h istologic grade, and proliferation indices as detected by MIB-1 (Ki-67) and p53 antibodies. Of the 19 PA, 14 showed no tumor growth by magnetic resona nce imaging, and had Ki-67 and p53 labeling indices (LI) of < 1%. The other 5 PA exhibited aggressive behavior manifest by marked diffuse infiltrative tumor growth causing death in 2 patients, 1 of whom was diagnosed with neu rofibromatosis type 1 (immunoperoxidase and radiographs not available), and marked local growth with an average time to growth of 39.3 months, a Ki-67 LI of 2-3%, and a p53 LI of < 1% in three others. Three of the five aggres sive PA histologically demonstrated a finely reticulated pattern, a pattern that appears as an exaggeration or expansion of the normal neuroglia of th e optic nerve, and may simulate a diffuse low-grade astrocytoma. Two demons trated the coarsely reticulated pattern, with the biphasic and microcystic pattern typical of PA. Three diffuse astrocytomas (2 anaplastic astrocytoma s and 1 glioblastoma) originated clinically and radiographically from the o ptic nerve, and revealed a Ki-67 LI of 2-12%, a p53 LI of 2-8%, and an aver age time to growth of 8 months. We conclude that the majority of PA of the optic nerve are non-aggressive, stabilize radiographically, and have Ki-67 and p53 LI < 1%. However, a subpopulation of PA has a propensity for aggres sive behavior, and are identified by a Ki-67 LI of 2-3% and a p53 LI of < 1 %. Diffuse astrocytomas have both Ki-67 and p53 LI > 2%. Thus, in cases of aggressive optic nerve tumors in which the histologic review of biopsy mate rial cannot confidently confirm the diagnosis of pilocytic or diffuse fibri llary glioma, a p53 LI of > 1% appears to favor the diagnosis of diffuse as trocytoma.