Epidural blood patch in a patient with an arachnoid cyst.

Arachnoid cysts are relatively common occurrences, with the majority being asymptomatic. The safety of an epidural blood patch in a patient with an arachnoid cyst has not been reported. Our patient had a known thoracic arachnoid cyst and required epidural blood patch for a postdural puncture headache. Magnetic resonance imaging obtained following the epidural blood patch demonstrated no alterations of the cyst or spinal cord compression.