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Spinal Arachnoid Cysts: Symptoms, Scans and Treatment

Spinal arachnoid cysts guide

By Mr Ahmed-Ramadan Sadek, Neurosurgeon · 12 min read

🎧 Listen to this guideAbout 7 minutes. Narrated in Mr Sadek’s voice using AI technology. General information only, not personal medical advice.

On this page

Key points

  • A spinal arachnoid cyst is a pocket of spinal fluid inside the spinal canal. Many cause no symptoms and are found by chance on an MRI scan done for something else.
  • Cysts are grouped by where they sit: outside the tough outer covering of the spinal cord (extradural) or inside it (intradural). This matters because the treatments differ.
  • When a cyst does cause trouble, the usual problems are back pain, nerve pain, numbness, weakness, unsteady walking and, less often, bladder or bowel changes.
  • A cyst that causes no symptoms usually needs no treatment. Surgery is considered when a cyst presses on the spinal cord or nerves and causes symptoms.
  • Most people improve after surgery, but the research is mainly small case series. Results are less good, and cysts come back more often, when the cyst followed scarring of the spinal coverings.

Go to A&E or call 999 straight away if you have:

  • Pain, tingling, weakness or numbness in both legs.[1]
  • Loss of feeling around your genitals or bottom (anus).[1]
  • Changes in your bladder or bowels, such as difficulty peeing, or peeing or pooing yourself.[1]
  • Changes in sexual feeling, such as how your penis or vagina feels during sex, or new problems getting or keeping an erection or reaching orgasm.[1]
  • New problems walking.[2]
  • A sudden loss of co-ordination, for example with tasks like buttoning a shirt.[2]
  • Back pain that started after a serious accident, such as a car accident, or back pain with chest pain.[1]

Problems with both legs, the bladder, bowels or sexual feeling can be signs of cauda equina syndrome. New walking or co-ordination problems can be a sign of pressure on the spinal cord (see our cervical myelopathy guide). Both need treatment in hospital as soon as possible. Do not drive yourself: ask someone to drive you, or call 999 for an ambulance.[1]

What is a spinal arachnoid cyst?

The spinal cord and its nerve roots are wrapped in layers called the meninges. The outer layer, the dura, is tough. Just inside it is a thin, web-like layer called the arachnoid. Under the arachnoid, clear cerebrospinal fluid (CSF, or spinal fluid) bathes the cord.

An arachnoid cyst is a pocket of spinal fluid trapped by the arachnoid. It can press on the spinal cord or on the nerve roots.[3] They are found most often in the thoracic spine (the part behind the chest), then the lower back, and least often in the neck.[3]

Extradural and intradural cysts

  • Extradural cysts sit outside the dura. Most are thought to form when spinal fluid leaks through a small hole or weak spot in the dura and collects outside it.[4] Finding and closing that hole is the key to treatment.[5]
  • Intradural cysts sit inside the dura, next to the spinal cord. Rarely, a cyst lies within the cord itself.[3]

The Nabors classification

Doctors often use a grading system from 1988, named after its first author, Nabors. It puts spinal cysts of the meninges into three groups:[6]

  • Type I: outside the dura, with no nerve roots inside the cyst. Extradural arachnoid cysts belong here.
  • Type II: outside the dura, with nerve root fibres in the cyst. These are not arachnoid cysts. Cysts that form on nerve roots, such as Tarlov cysts, are covered in our Tarlov cyst guide.
  • Type III: inside the dura. Intradural arachnoid cysts belong here.

Newer systems have since been proposed, but the Nabors groups are still used in recent studies.[7][8]

What causes them?

Often there is no clear cause. These are called primary (or idiopathic) cysts, and some may be present from birth.[9][10] In other people the cyst follows something that inflamed or scarred the arachnoid. These are called secondary cysts. Reported triggers include:[7][11][12]

  • spinal surgery or other procedures on the spine, such as a spinal anaesthetic, lumbar drain or injections into the spinal fluid
  • an injury to the spine
  • bleeding around the brain or spinal cord (subarachnoid haemorrhage)
  • infection, such as meningitis

Several of these can cause arachnoiditis, a long-lasting inflammation and scarring of the arachnoid. Secondary cysts are often linked to arachnoiditis, which makes them harder to treat.[11][7] In a series of 18 people having surgery, 15 had cysts thought to be congenital, 2 developed one after a lumbar drain and 1 after a spinal anaesthetic.[12]

How common are they?

Spinal arachnoid cysts are rare. One review put them at about 1 to 2 in 100 of all cystic masses in the spine.[3] Another said extradural cysts make up fewer than 1 in 100 of all lesions in the space outside the dura.[4] In one specialist surgeon’s series of 1,519 people with space-occupying lesions in the spine, 130 (about 9 in 100) had intradural arachnoid cysts.[7] These figures come from hospital series, so they do not tell us how common cysts are in the general population. We did not find a reliable figure for that.

Found by chance on a scan

Many cysts cause no symptoms and turn up on an MRI done for another reason.[13] In the largest imaging series of extradural cysts, 62 in 100 were found by chance, and most stayed the same over time.[8] If this is how your cyst was found, the main question is whether it explains any symptoms you have.

Symptoms

Symptoms depend on where the cyst is and what it presses on.[10] Symptoms tend to build up slowly. In two surgical series, people had had symptoms for an average of 15 months before diagnosis.[14][15] Common problems include:

  • Back or neck pain, often in the middle of the back.[14][9]
  • Nerve pain spreading into a leg or arm, or burning, tingling and pins and needles.[16][8]
  • Numbness or weakness in the legs, or less often the arms.[14][17]
  • Unsteady walking or clumsiness, from pressure on the spinal cord (myelopathy).[14][17] See our cervical myelopathy guide for more on spinal cord compression.
  • Bladder or bowel changes, which are less common.[14]

How often each symptom appears varies between studies. Among adults having surgery, back pain was reported by 53 to 73 in 100,[18][14] walking problems by 12 to 80 in 100[18][14][17] and bladder or sphincter problems by about 18 in 100.[14] Walking problems and weakness were much more common in one series of intradural cysts than in one series of extradural cysts.[17][18]

Symptoms that come and go

Symptoms can come and go. An older study described intermittent nerve root symptoms as typical of intradural arachnoid cysts.[19] Moving-picture MRI has shown a cyst pressing on the cord in a changing way as spinal fluid moves,[20] and one surgical series suggested cysts cause both constant and changing pressure on the cord.[16] We did not find good studies on whether symptoms change with body position or straining. Rarely, an extradural cyst that keeps draining spinal fluid has been linked to low fluid pressure around the brain (intracranial hypotension).[3]

A fluid cavity in the cord (syrinx)

Some intradural cysts disturb the flow of spinal fluid enough to cause a fluid-filled cavity inside the spinal cord, called a syrinx. In surgical series a syrinx was found in about 25 to 46 in 100 people with mainly primary cysts,[15][16][7] and in 86 in 100 with secondary cysts.[7] Our Chiari malformation guide explains syringomyelia in more detail.

Scans and tests

MRI is the main scan. It shows the cyst, how long it is and how much it presses on the cord or nerves.[6][10] See our MRI guide. NICE advises against routine scans for back pain in a non-specialist setting such as a GP surgery, and advises considering a scan in specialist care only when the result is likely to change treatment.[21] A cyst that is found by chance is a good example of why: a scan can show things that are not causing your pain.

If surgery is being considered, extra tests may be used to find a hole in the dura or a link between the cyst and the normal spinal fluid space:

  • CT myelography. Dye is injected into the spinal fluid and a CT scan shows whether and where it enters the cyst.[6][10] In one series, 57 in 100 people with intradural cysts had this test.[15]
  • Dynamic or digital subtraction myelography. X-ray pictures are taken quickly as the dye flows, sometimes with you lying on your side, to catch the moment it passes through a hole in the dura.[22][5]
  • Cine (moving-picture) or flow MRI. Special MRI sequences show how spinal fluid moves and whether the cyst presses on the cord as the fluid pulses.[20][5]

Finding the hole can be hard, and specialists often combine several tests.[5]

Conditions that can look similar

  • Arachnoid web. A thin band of arachnoid, usually behind the cord in the upper back, that dents the cord and blocks fluid flow. In a review of 43 people, 67 in 100 also had a syrinx. Webs can be hard to see on scans.[23]
  • Spinal cord herniation. In one series of 22 adults, 2 cysts were judged on imaging to be a bulge of the cord through the dura instead, and the scans were inconclusive in 3 more.[14]
  • Syrinx. A cavity inside the cord, not beside it. See our Chiari malformation guide.
  • Tarlov cysts. These form on nerve roots, most often at the base of the spine (sacrum), and most cause no symptoms.[24] See our Tarlov cyst guide.

When watching is reasonable

NICE has no guidance specific to spinal arachnoid cysts. Its only related guidance, from 2007, covers draining spinal cysts with a needle (see below).[24]

If a cyst causes no symptoms, one review advised no treatment, whatever its size.[13] Most extradural cysts found by chance in one series stayed stable over time.[8] When symptoms are mild, the choice is a balance between the possible benefit of surgery and its risks. One review advised early surgery for people with significant weakness or other nerve damage caused by a cyst.[3] There is no agreed schedule for repeat scans. Your specialist may suggest one if you have symptoms, or ask you to report changes instead.

If you are being watched, tell your GP or specialist team promptly about new or worsening numbness, weakness, walking problems or bladder or bowel changes. These can mean the cyst is pressing harder on the cord or nerves.

Treatment

Surgery is the main treatment for cysts that cause symptoms by pressing on the cord or nerves.[13][25] NICE notes that painful spinal cysts are often managed first with pain relief, and that open surgery may be needed if the pain does not respond or there is a threat of permanent nerve damage.[24] Ask a pharmacist or your GP which painkillers suit you.

Extradural cysts

The standard operation is to remove all or most of the cyst and close the hole in the dura, either by stitching it or with a patch.[4][26] Closing the hole is the step that matters most. In a series of 34 people, no cyst came back in those whose dural defect was repaired, over an average follow-up of 80 months.[18] A review of extradural cysts where no link to the spinal fluid had been shown found that only 1 of 20 people had a recurrence, and that recurrence was much more likely if the dural defect was not dealt with.[10] Some specialists now ask whether the cyst wall must be removed at all, or whether closing the hole alone is enough, and suggest these cysts may be a type of spinal fluid leak.[22]

Intradural cysts

Three approaches are used:[27]

  • Resection: removing the cyst wall, completely or in part.
  • Fenestration or marsupialisation: opening the cyst wall widely so the fluid can drain freely into the normal spinal fluid space.
  • Shunting: placing a thin tube to drain the cyst, either into the normal spinal fluid space or into a body cavity such as the abdomen. This is mainly considered for cysts that cannot be removed.[11]

A systematic review of 19 studies with 414 people found that all these methods have worked, and that the best choice depends on the person and the cyst.[27] Another review found no evidence that one method is better than another.[25] Studies differ on the detail:

  • In a series of 72 adults, fenestration and resection gave similar shrinkage and quality of life for cysts without internal walls (septa).[17]
  • In a series of 18 people, 4 of the 7 who had fenestration later needed the cyst removed because their symptoms did not improve. The authors advised removal when the cyst has internal strands (trabeculation).[12]
  • For secondary cysts, a review found recurrence at 12 months of about 21 in 100 after resection and 51 in 100 after fenestration.[11]
  • Some surgeons also widen the dura with a patch (expansile duraplasty) to restore fluid flow. In one series, people with pain who had this were more likely to get pain relief.[15][25]

Draining with a needle

NICE says the evidence for draining spinal cysts with a needle under scan guidance is very limited. It found one report of a single person with an arachnoid cyst. NICE says it can be used for this rare condition provided normal arrangements for clinical governance and audit are in place, and that patients should be told the benefits are uncertain and further treatment may be needed.[24]

Outcomes and risks of surgery

Most people improve, but how many depends on the study and on what counts as improvement:

  • About 60 to 70 in 100 improved in a series of 21 people with intradural cysts.[15]
  • 90 in 100 had a good outcome in a 2025 series of 29 people.[28]
  • 97 in 100 improved in a series of 104 people with cysts of the dura, with and without nerve roots inside.[26]
  • On scans after surgery, the cyst had gone completely in 14 of 16 people in one series.[14]

The type of cyst matters. In a large series, 83 in 100 people with primary cysts had no worsening 10 years after surgery, compared with 15 in 100 with secondary cysts.[7] A review found people with primary cysts were more than twice as likely to improve as those with secondary cysts, and advised caution with surgery for secondary cysts.[9]

Which symptoms improve

Weakness and walking tend to improve most.[15][16] Studies disagree on pain. In one series, pain was the symptom least likely to settle (50 in 100),[15] and in another, burning nerve pain went away in only 29 in 100.[16] A third series found pain and weakness improved most and numbness least.[29]

Risks

  • Overall complications: about 9 to 15 in 100 in recent series.[26][28] In one of these, none left lasting problems.[28]
  • Spinal fluid leak: fluid can collect under the wound (a pseudomeningocele). This happened in about 4 in 100 people in one series, with slow wound healing in about 5 in 100.[26]
  • Further surgery: 9 of 72 people (about 13 in 100) needed a further operation in one series, mostly because the cyst did not shrink enough. Most of these cysts had internal walls or followed bleeding.[17]
  • Recurrence: commoner with secondary cysts and arachnoiditis.[11][7] Very late recurrence is possible: one case report describes a cyst returning 29 years after surgery.[30]
  • Bleeding or infection: uncommon. One series reported one delayed wound infection in 19 operations.[14]

Recovery and follow-up

Recovery depends on the operation and on how much the cord or nerves were affected beforehand. In one large series, people with primary cysts improved markedly in the first year after surgery.[7] Your surgical team will give you advice about wound care, activity, driving and returning to work. Ask them about these before you go home.

Surgical series have used MRI after the operation to check that the cyst has shrunk.[14][17] Because cysts can come back, sometimes years later,[30][7] keep a copy of your scan reports and tell any new doctor about your previous surgery.

The evidence and its limits

Spinal arachnoid cysts are rare, so almost all the evidence comes from case series from single hospitals, often looking back at records, and from reviews that pool those series.[27][25] There are no trials comparing surgery with watching, or one operation with another. Studies use different definitions and outcome measures, so their numbers are hard to compare. This is why the figures in this guide are given as ranges.

When to get help

See your GP if your back pain does not improve after a few weeks of treating it at home, is stopping you doing day-to-day activities, is worse at night, or is coming from the top of your back between your shoulders.[1]

For emergencies, see the red box above. Ask for an urgent GP appointment or get help from NHS 111 if you have back pain and feel hot, cold, shivery or generally unwell, or if severe pain starts suddenly or gets worse quickly.[1] Do the same if you have heaviness or weakness in your arms or legs.[2]

If a cyst has been found and you are unsure whether it explains your symptoms, or you have been offered surgery, you may find a second opinion helpful.

Questions to ask

  • Is my cyst extradural or intradural, and is it primary or secondary?
  • Do you think the cyst explains my symptoms, or was it found by chance?
  • Is the cyst pressing on my spinal cord or nerves?
  • Do I need more tests to look for a hole in the dura?
  • If we watch it, what changes should make me get in touch, and will I need another scan?
  • If I have surgery, which operation do you suggest and why? What are the chances of the cyst coming back?

Frequently asked questions

Is a spinal arachnoid cyst a tumour or cancer?

No. It is a pocket of spinal fluid, not a growth of tissue.[3] Many cause no symptoms at all and are found by chance on a scan.[13]

My scan found a cyst by chance. Do I need surgery?

Usually not. If a cyst causes no symptoms, one review advised no treatment whatever its size.[13] In a series of extradural cysts, 62 in 100 were found by chance and most stayed the same over time.[8] Your specialist will check whether it could explain any symptoms you have.

Can an arachnoid cyst cause back pain?

It can. Back pain was one of the commonest symptoms in surgical series.[14][18] But a cyst seen on a scan is not always the cause of back pain, which is why your specialist will compare the scan with your symptoms and examination.

Will my cyst get bigger?

Most cysts found by chance seem to stay the same size.[8] Some do press on the cord or nerves and cause symptoms,[3] which is why new or worsening numbness, weakness or walking problems should be reported promptly.[13]

Why do I need a myelogram as well as an MRI?

MRI shows the cyst well, but it often does not show the small hole in the dura that feeds an extradural cyst. A CT myelogram, or a faster dynamic myelogram, can show where dye enters the cyst, which helps the surgeon plan where to operate.[6][22][5]

Can the cyst come back after surgery?

It can. For extradural cysts, recurrence is uncommon when the hole in the dura is closed.[18][10] For intradural cysts it is more common, especially after infection, bleeding or surgery has scarred the arachnoid.[11][7] Very late recurrence has been reported.[30]

Is this the same as a Tarlov cyst?

No. Tarlov cysts form on nerve roots, mostly at the base of the spine, and most cause no symptoms.[24] See our Tarlov cyst guide.

Further reading

References

  1. NHS. Back pain. NHS website; page last reviewed 5 March 2026. Link
  2. NHS. Cervical spondylosis. NHS website; page last reviewed 2 August 2023. Link
  3. Epstein NE. Review/Perspective on the diagnosis and surgical management of spinal arachnoid cysts. Surg Neurol Int. 2022;13:98. Link
  4. Messerer R, Aldugman M, Morgado A, Barrey C. Spinal extradural arachnoid cysts: a rare entity and review of the literature. Eur Spine J. 2024;33(3):872-880. Link
  5. Jian Q, Liu Z, Duan W, Jian F, Chen Z. How to locate the dural defect in a spinal extradural meningeal cyst: a literature review. Chin Neurosurg J. 2022;8(1):27. Link
  6. Nabors MW, Pait TG, Byrd EB, et al. Updated assessment and current classification of spinal meningeal cysts. J Neurosurg. 1988;68(3):366-377. Link
  7. Klekamp J. A new classification for pathologies of spinal meninges, part 2: primary and secondary intradural arachnoid cysts. Neurosurgery. 2017;81(2):217-229. Link
  8. Ahmed AK, Anisetti B, Huynh T, et al. Clinical and imaging features of spinal extradural arachnoid cysts: a retrospective study of 50 cases. Neuroradiology. 2022;64(12):2409-2416. Link
  9. Cuoco JA, Muthukumar S, Rogers CM, et al. Spinal intradural arachnoid cysts in adults: an institutional experience and literature review. Neurosurgery. 2023;92(3):450-463. Link
  10. Khan MSI, Ahmed N, Barua KK, et al. Pathogenesis, management strategies, and outcome of non-communicating extradural spinal arachnoid cyst (NEAC): a systematic review. Br J Neurosurg. 2023;37(2):213-219. Link
  11. Wang YB, Wang DH, Deng SL. Symptomatic secondary spinal arachnoid cysts: a systematic review. Spine J. 2023;23(8):1199-1211. Link
  12. Ramazanoglu AF, Sarikaya C, Varol E, et al. Surgical treatment of spinal arachnoid cysts: cyst excision or fenestration? Turk Neurosurg. 2022;32(6):1002-1006. Link
  13. Hughes G, Ugokwe K, Benzel EC. A review of spinal arachnoid cysts. Cleve Clin J Med. 2008;75(4):311-315. Link
  14. Fam MD, Woodroffe RW, Helland L, et al. Spinal arachnoid cysts in adults: diagnosis and management. A single-center experience. J Neurosurg Spine. 2018;29(6):711-719. Link
  15. Moses ZB, Friedman GN, Penn DL, Solomon IH, Chi JH. Intradural spinal arachnoid cyst resection: implications of duraplasty in a large case series. J Neurosurg Spine. 2018;28(5):548-554. Link
  16. Sadek AR, Nader-Sepahi A. Spinal arachnoid cysts: presentation, management and pathophysiology. Clin Neurol Neurosurg. 2019;180:87-96. Link
  17. Schmutzer M, Tonn JC, Zausinger S. Spinal intradural extramedullary arachnoid cysts in adults: operative therapy and clinical outcome. Acta Neurochir (Wien). 2020;162(3):691-702. Link
  18. Cai Z, Hong X, Huang J, et al. Microsurgical treatment of symptomatic spinal extradural arachnoid cyst: a consecutive case series of 34 patients and literature review. Clin Neurol Neurosurg. 2021;210:107000. Link
  19. Fortuna A, Mercuri S. Intradural spinal cysts. Acta Neurochir (Wien). 1983;68(3-4):289-314. Link
  20. Shimizu H, Tominaga T, Takahashi A, Yoshimoto T. Cine magnetic resonance imaging of spinal intradural arachnoid cysts. Neurosurgery. 1997;41(1):95-100. Link
  21. National Institute for Health and Care Excellence. Low back pain and sciatica in over 16s: assessment and management (NG59). Published 30 November 2016, last updated 29 July 2026. Link
  22. Mamlouk MD, Zamary AR, Lützen N, et al. Decubitus myelography for spinal extradural arachnoid cyst: better classified as a lateral dural CSF leak? AJNR Am J Neuroradiol. 2025;46(12):2693-2696. Link
  23. Nisson PL, Hussain I, Härtl R, Kim S, Baaj AA. Arachnoid web of the spine: a systematic literature review. J Neurosurg Spine. 2019;31(2):175-184. Link
  24. National Institute for Health and Care Excellence. Therapeutic percutaneous image-guided aspiration of spinal cysts (HTG143, formerly IPG223). Published 27 June 2007, last updated 1 August 2007. Link
  25. Kalsi P, Hejrati N, Charalampidis A, et al. Spinal arachnoid cysts: a case series and systematic review of the literature. Brain Spine. 2022;2:100904. Link
  26. He G, Xue X, Chen X, et al. A novel subtype classification and corresponding surgical strategies for spinal dural cysts: a report of 104 cases. Spine J. 2024;24(12):2322-2333. Link
  27. Baig Mirza A, Bartram J, Vastani A, et al. Systematic review of surgical management of spinal intradural arachnoid cysts. World Neurosurg. 2022;158:e298-e309. Link
  28. Imwinkelried L, Nasiri D, Schär RT, et al. Surgical outcomes for spinal arachnoid cysts and webs: a case series. Acta Neurochir (Wien). 2025;167(1):248. Link
  29. Eroglu U, Bozkurt M, Kahilogullari G, et al. Surgical management of spinal arachnoid cysts in adults. World Neurosurg. 2019;122:e1146-e1152. Link
  30. Nakahashi M, Uei H, Tokuhashi Y. Recurrence of a symptomatic spinal intradural arachnoid cyst 29 years after fenestration. J Int Med Res. 2019;47(9):4530-4536. Link

This article is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist before making any change to your treatment.

Last checked: October 2026