Use of Doppler ultrasonography to detect an elusive communication of a spinal extradural arachnoid cyst.

Spinal extradural arachnoid cysts are thought to be extradural arachnoid pouches that communicate with the intraspinal subarachnoid space through a small dural defect. The mainstay of current treatment is resection of the cyst wall followed by obliteration of the communicating pedicle. Despite its clinical importance, the communicating pedicle of the cyst is often elusive. The authors report a 57-year-old woman with an extradural arachnoid cyst with intractable back pain and progressive motor weakness. Preoperative imaging studies, including phase-contrast MRI, failed to identify the communicating pedicle. Intraoperative Doppler ultrasonography clearly demonstrated the pulsatile influx of cerebrospinal fluid into the cyst. A flap-like structure was also noted near the pedicle; this structure appeared to act as a one-way valve. Doppler ultrasonography may be a helpful adjunct for identifying the location of elusive communication in a spinal extradural arachnoid cyst.