A Case of Mistaken Identity

The procedure was a ventriculoperitoneal shunt and biopsy of the mass. The biopsy showed microvascular proliferation, infiltrative growth, mitotic figures, areas of necrosis, and a MIB-1 proliferation index of 22%, characteristics of a high-grade glioma. The patient's chemotherapy was changed to a drug regimen appropriate for this tumor (CCG protocol 9921 induction regimen A). The 3 rd most common malignant brain tumors in children under 2 years (1), high-grade gliomas, usually occur in the cerebral hemispheres with only 11-24% arising from the diencephalic region, the presumed source in our patient (2, 3). Because malignant brain tumors rarely arise in this region in young children, and because pilocytic astrocytomas commonly originate in this region, are known to enhance avidly, and typically grow without invading brain, we believed that pilocytic astrocytoma was a strong enough presumptive diagnosis to preclude the need for biopsy. We were wrong. Although high-grade gliomas of youths and adults are pathologically indistinguishable, there are differences in tumor behavior. High-grade gliomas in very young patients are remarkably chemosensitive, with a 5-year overall survival rate of over 50% with appropriate multi-drug chemotherapy (4). Still unresolved issues are whether age at diagnosis, histologic features of malignancy, or the degree of surgical resection influence prognosis (4).