In normal patients, blood and cerebrospinal fluid (CSF) contain circulating cells and other molecules such as proteins and nucleic acids. In patients with central nervous system (CNS) and other conditions, the levels of these molecules may be altered. In several other studies at our institution, the investigators are investigating such molecules in tumor specimens as well as the blood and cerebrospinal fluid of pediatric patients with CNS tumors. However, these levels are difficult to interpret without comparing them to levels in patients without CNS tumors. The investigators propose a study to collect small amounts of blood and cerebrospinal fluid from pediatric patients without CNS tumors who are undergoing a diagnostic or therapeutic neurosurgical procedure aimed at addressing altered CSF dynamics.