Natural Dural Defect of the Posterior Fossa Dura as a Risk Factor for Postoperative Cerebrospinal Fluid Leakage.

BACKGROUND: During microvascular decompression surgery (MVD), small (2-3 mm diameter) natural dural defects have been noticed occasionally but never reported. These tiny dural defects cannot be detected by preoperative imaging studies or even in anatomical cadaver dissection, but may lead to complications including cerebrospinal fluid (CSF) leakage. Our objective was to analyze the features of these natural defects in the posterior fossa dura. METHODS: Surgical reports and videos of 593 consecutive patients who underwent MVD surgery for trigeminal neuralgia (TN) or hemifacial spasm (HFS) were analyzed retrospectively. Video recording confirmed that these small holes were not related to the craniotomy procedure itself and were natural defects. RESULTS: Such natural defects of the posterior fossa dura were found in 6 of the 593 patients. All of the defects were about 2 mm in diameter and occurred on the left side in female patients with HFS. All were managed by patching with a fascial or muscle graft. Multivariate analysis showed that the defect was significantly associated with the left side and had a female predilection. Neither disease (HFS or TN) nor age was correlated with the presence of dural defects. CONCLUSIONS: After posterior fossa craniotomies, CSF leakage or pseudomeningocele may occur at the dural suture site because of the hydrostatic pressure. Because such natural dural defects may be a cause of CSF complications after posterior fossa surgery, their possible occurrence should be considered. This is the first report to document the occurrence of such natural defects of the posterior fossa dura.