Review/Perspective On the Diagnosis and Surgical Management of Spinal Arachnoid Cysts.

Background: Spinal arachnoid cysts (SAC) are typically congenital, spontaneous, traumatic (i.e., including iatrogenic/surgical), or inflammatory in origin. In descending order, they occur in the thoracic, lumbar, and cervical spine, and originate from focal entrapment of the arachnoid membrane. Arachnoid cysts represent 1-2% of all cystic spinal masses/tumors. The majority are extradural arachnoid cysts (EDAC) while 10% of all arachnoid cysts are intradural (IDAC) including subarachnoid, or extra-arachnoidal/subdural. Only rarely are they intramedullary in location. The clinical symptoms/signs of IDAC/EDAC include; intracranial hypotension (i.e., due to continued cerebrospinal fluid drainage), radiculopathy, and/or myelopathy. Methods: Magnetic Resonance Images (MR) and Myelo-Computed Tomography (Myelo-CT) studies classically document the predominant dorsal location of IDAC/EDAC. They also show their extent and severity contributing to root, cord, and/or cauda equina compression. In the cervical/thoracic spine, MR/Myelo-CT studies classically show the "double cord" or "windsock" signs, while the "fake arachnoiditis sign" may be seen in the lumbar spine. The latter sign signals the presence of a circumferential extra-arachnoidal-subdural cyst that centrally "traps" the cauda equina. Note, that this resembles and is often misinterpreted as adhesive archnoiditis. Results: Patients with significant SAC-related neurological deficits typically warrant early surgery. That surgery includes; partial/total resection/fenestration of cyst walls, and occlusion of communicating fistulas with or without accompanying shunts. Conclusion: It is critical to recognize the clinical (i.e., intracranial hypotension, radiculopathy, and/or myelopathy) and radiographic MR/Myelo-CT signs (i.e., "double cord," "windsock signs", or "fake arachnoiditis sign") of IDAC, EDAC, or intramedullary spinal arachnoid cysts to appropriately offer treatment. For those with significant neurological deficits, early surgery (i.e. optimally 0-< 24 hours after the onset of symptoms/signs consisting of laminectomies, partial/total cyst resection/fenestration, and ligation/occlusion of the subarachnoid-cyst fistula with or without shunt placement), is essential to avoid significant permanent neurological sequelae.