The association of hydrocephalus with intramedullary spinal cord tumors: a series of 25 patients. 171 patients with intramedullary spinal cord tumors were operated on, of which 25 patients (15%), mostly children, developed symptomatic hydrocephalus. Twenty patients (12%) had malignant tumors, with 13 of the 20 cases (63%) complicated by increased intracranial pressure and ventriculomegaly. Of the remaining 151 patients with benign tumors (89%), only 12 (8%) developed symptomatic hydrocephalus. In an effort to understand the relationship between hydrocephalus and intramedullary spinal cord tumor, the authors analyze the level and histology of the neoplasm, as well as its association with spinal cysts. A review of the neurosurgical literature reveals that 34 similar cases of hydrocephalus associated with intramedullary spinal cord tumors have been reported to date. The authors note that the presence of hydrocephalus in patients with malignant intramedullary astrocytomas is associated with a shorter rate of survival than in those patients with high-grade lesions but without hydrocephalus, apparently due to rapid tumor progression. The ventriculomegaly seen with benign spinal cord gliomas has no statistically significant effect upon long-term prognosis. 