Objective: This study was conducted to determine whether arachnoid tissue or cerebrospinal fluid (CSF) sampling is valuable for risk stratification in children with posterior fossa brain tumors.
Methods: Arachnoid tissue and CSF from the cisterna magna (CSFCM) was sampled at the time of primary tumor resection. Results were compared with conventional staging methods (M stage) and correlated with patient outcome.
Results: Eighty-three patients were enrolled in the study. Arachnoid infiltration was identified in 11 of 80 (13.8%) and CSFCM was positive in 20 of 77 (26.0%) specimens. Arachnoid infiltration and CSF cytology were found in 20.0% and 44.8%, respectively, for medulloblastoma/pineoblastoma (primitive neuroectodermal tumor), 6.9% and 3.6% for pilocytic astrocytoma, and 0.0% and 33.3% for ependymoma. The 3-year event-free survival (EFS) was negatively influenced by either arachnoid infiltration (40.9% arachnoid positive versus 65.4% arachnoid negative; P = 0.23) or CSFCM positivity (52.6% CSFCM positive versus 67.1% CSFCM negative; P = 0.03). The 3-year EFS for patients with primitive neuroectodermal tumor who had positive arachnoid sampling was 33.3%, compared with 67.3% in patients who had no evidence of arachnoid infiltration (P = 0.26). The 3-year EFS for patients with primitive neuroectodermal tumor who had positive CSFCM was 50.0% compared with 67.5% in patients who had negative cytological analysis of CSFCM (P = 0.07). Arachnoid infiltration and CSF sampling were congruous with M stage in 73.3% and 86.2% of patients, respectively.
Conclusion: Intraoperative evidence of arachnoid infiltration or CSFCM dissemination in patients with posterior fossa brain tumors occurs at a variable frequency that is dependent on tumor type, correlates with conventional M stage, and may be predictive of outcome.