Spinal Arachnoid Cyst
A cerebrospinal fluid-filled sac that forms within the arachnoid membrane and can compress the spinal cord or nerves.
ICD-10: G96.19 · systemic condition
A spinal arachnoid cyst is a benign, cerebrospinal fluid-filled sac that develops within or adjacent to the arachnoid mater — the middle of the three protective membranes (meninges) surrounding the spinal cord. Most spinal arachnoid cysts are located within the intradural space (inside the dura but outside the cord) and contain fluid identical in composition to normal CSF. Many are discovered incidentally on MRI obtained for unrelated reasons and never cause symptoms. When a cyst is large enough or positioned such that it compresses the spinal cord or nerve roots, it can produce myelopathy (cord dysfunction) or radiculopathy (nerve root pain) at the affected level. Symptoms tend to develop gradually and may fluctuate with position or activity, as changes in CSF pressure alter cyst size. Thoracic spinal arachnoid cysts are the most common, followed by cervical and lumbar locations. Treatment is reserved for symptomatic cysts that are clearly compressing neural structures. Surgical options include microsurgical fenestration (creating an opening in the cyst wall to allow communication with the subarachnoid space) or excision of the cyst wall. Many patients experience significant neurological improvement after surgery, particularly when treated before permanent cord damage has occurred.
Anatomy & Pathology
The spinal meninges consist of three layers: the outer dura mater, the middle arachnoid mater, and the inner pia mater. The subarachnoid space — between the arachnoid and the pia — is where CSF circulates. Arachnoid cysts form when a split or duplication occurs within the arachnoid membrane, trapping fluid in a sealed pocket. Extradural arachnoid cysts can also occur when CSF herniates through a small dural defect into the epidural space.
Symptoms
- Progressive back or neck pain at the level of the cyst
- Myelopathy — weakness, stiffness, or gait difficulty if the thoracic or cervical cord is compressed
- Radicular pain or numbness radiating into the arms or legs along a dermatomal pattern
- Bladder and bowel dysfunction in larger cysts with significant cord compression
- Symptoms that worsen with exertion or position changes and improve with rest
- Incidental finding without any symptoms in many patients
Causes & Risk Factors
- Congenital — arachnoid cysts that form during embryonic development as the meninges develop
- Idiopathic — no identifiable cause in the majority of cases
- Post-inflammatory — scarring from meningitis, arachnoiditis, or subarachnoid hemorrhage can create cyst-like pockets
- Post-traumatic — spinal injury or surgery can disrupt the arachnoid membrane and lead to cyst formation
- Iatrogenic — following lumbar puncture or intrathecal procedures in rare cases
Treatment Options
Conservative
- Observation with serial MRI for asymptomatic or mildly symptomatic cysts that are stable in size
- Activity modification if symptoms correlate with specific postures or exertion
- Pain management with NSAIDs or neuropathic agents for mild symptoms
- Physical therapy to maintain strength and mobility in patients with mild myelopathy
Surgical
- Microsurgical fenestration — opening the cyst wall to allow CSF communication and equalize pressure, decompressing the cord
- Cyst excision — complete or partial removal of the cyst wall; more definitive but technically demanding
- CT-guided percutaneous aspiration — temporary decompression, rarely curative due to high recurrence rate
- Cystoperitoneal or cystosubarachnoid shunting for cysts not amenable to fenestration
- Intraoperative neurophysiological monitoring to protect the cord during dissection
When to see a spine specialist
Seek medical evaluation if you have progressive back or neck pain, worsening leg weakness or gait instability, or new bladder or bowel problems. These may indicate that a known or previously asymptomatic arachnoid cyst is growing and compressing the spinal cord. Early surgical treatment before permanent cord damage offers the best chance of neurological recovery.
Specialists Who Treat Spinal Arachnoid Cyst
Find a specialist who treats spinal arachnoid cyst
NPI-verified spine surgeons in your city.
- Austin, TX
- Charlotte, NC
- Chicago, IL
- Columbus, OH
- Dallas, TX
- Denver, CO
- Fort Worth, TX
- Houston, TX
- Indianapolis, IN
- Jacksonville, FL
- Los Angeles, CA
- Nashville, TN
- New York, NY
- Philadelphia, PA
- Phoenix, AZ
- San Antonio, TX
- San Diego, CA
- San Francisco, CA
- San Jose, CA
- Seattle, WA
Find a spine specialist near you
Browse NPI-listed spine surgeons and neurosurgeons who treat spinal arachnoid cyst. Filter by location, insurance, and availability.
Search spine specialists →Frequently Asked Questions
Are spinal arachnoid cysts dangerous?
Most spinal arachnoid cysts found incidentally are not dangerous and never cause problems. A minority grow large enough to compress the spinal cord or nerve roots, at which point they can cause significant neurological deficits. The key is surveillance — serial MRI allows detection of growth before irreversible damage occurs.
How is a spinal arachnoid cyst different from a Tarlov cyst?
Tarlov cysts (perineural cysts) arise from the nerve root sheath — specifically from the space between the endoneurium and perineurium of sacral nerve roots — and are almost exclusively found at the sacral level. Spinal arachnoid cysts arise from the arachnoid membrane and can occur at any spinal level. Both can be asymptomatic incidental findings, but they have different anatomical origins, locations, and surgical approaches.
Will the cyst come back after surgery?
Recurrence depends on the surgical technique. Complete excision has a lower recurrence rate than fenestration alone, but complete excision is not always possible without risking injury to adherent neural tissue. Fenestration is effective in many patients but cysts can re-form if the opening scars over. Long-term MRI follow-up after surgery is recommended regardless of technique.