Syringomyelia in Chiari malformation

Syringomyelia is the presence of a syrinx, a fluid-filled cavity inside the spinal cord1. It is the most serious complication of Chiari I, because an enlarging syrinx damages the spinal cord from the inside.

Why a syrinx forms

In Chiari I, the tonsils plug the foramen magnum and disturb the normal back-and-forth flow of cerebrospinal fluid (CSF) between the head and the spine. Over time, fluid is driven into the spinal cord and collects in a cavity, usually in the neck and upper back2. How this happens exactly is still debated. Older theories proposed that pressure waves are forced down the central canal of the cord; others that straining creates a pressure difference between head and spine that drives fluid into the cord2.

How often Chiari I comes with a syrinx is uncertain. Older figures came mostly from surgical series, which select the more severe cases, and the true proportion is likely lower than the literature suggests3. Chiari 0 describes a syrinx with less than 5 mm of tonsillar descent, thought to result from crowding at the foramen magnum2.

Symptoms

A syrinx in the neck first affects the nerve fibers that cross the center of the spinal cord, which carry pain and temperature. The typical symptoms are2:

• loss of pain and temperature sensation across the shoulders and upper arms, often with touch preserved
• unnoticed burns and cuts on the hands
• neck, shoulder and arm pain
• weakness and wasting of the hand muscles
• later, stiffness and weakness in the legs

Some syrinxes stay the same size for years and cause no symptoms. Others enlarge and cause progressive loss of function. Progression, on imaging or in symptoms, is the main reason for follow-up scans.

Scoliosis in children

A syrinx is a known cause of scoliosis in children. In a study of 43 children with Chiari I and a spinal curve of 10° or more, about half had a syrinx, and they were more likely to have a curve over 20° (86% against 41%). Over about three years, 77% of the curves stayed stable, 16% progressed and 7% improved; every curve that improved had been 20° or less, and none of those children had a syrinx4. In children who had decompression alone, curves changed at a similar rate before and after surgery4.

Decompression is done to protect the spinal cord. It shouldn't be presented as a treatment for the curve, which is managed on its own terms.

Treatment

When a syrinx comes with Chiari I, the first operation is decompression at the foramen magnum, not drainage of the syrinx. Restoring CSF flow removes the cause, and the syrinx then shrinks on its own in most patients5. In 12 pooled observational studies using intraoperative ultrasound during Chiari I surgery, the syrinx improved or resolved in 87%6.

Opening the dura and enlarging it with a patch (duraplasty) appears to help the syrinx shrink. US guidelines note that a dural patch may improve syrinx resolution5, and in the pooled studies using intraoperative ultrasound, duraplasty was associated with better syrinx outcomes6. In a 2026 randomized trial of 162 children and young adults with a syrinx, the syrinx shrank by an average of 3.08 mm with duraplasty and 1.22 mm without, and repeat decompression was needed in 3% against 14%7. The surgery page sets out the trade-offs.

How quickly a syrinx shrinks

A syrinx shrinks slowly, over months to a year or more, and imaging often lags behind how a person feels. Symptom relief and syrinx shrinkage don't correspond closely: one can improve without the other5. Sensory loss that was present before surgery often persists after the cavity has shrunk, because the damage was to the spinal cord itself.

US guidelines suggest that further surgery may be considered if a syrinx has not improved on imaging 6 to 12 months after decompression5. The first question is then whether the decompression was adequate. Draining the syrinx directly with a shunt is a later option.

Syrinx without symptoms

A syrinx found by chance, without symptoms, is often watched with repeat MRI rather than operated on immediately; the decision then follows how it behaves. US guidelines advise against preventive surgery only for Chiari I without a syrinx8, so a syrinx shifts the discussion even when it causes no symptoms.

Syringomyelia without Chiari

A syrinx can also follow spinal cord injury, meningitis, a spinal tumor or tethering of the spinal cord. These forms have different causes and treatments; the international consensus on Chiari and syringomyelia in adults treats isolated syringomyelia as a separate topic9.

References

1. National Institute of Neurological Disorders and Stroke. Chiari malformation. BrainFacts.org. Accessed October 3, 2026. Source ↩
2. Rosenblum JS, Pomeraniec IJ, Heiss JD. Chiari malformation (update on diagnosis and treatment). Neurol Clin. 2022;40(2):297-307. doi:10.1016/j.ncl.2021.11.007 Source ↩
3. Holste KG, Muraszko KM, Maher CO. Epidemiology of Chiari I malformation and syringomyelia. Neurosurg Clin N Am. 2023;34(1):9-15. doi:10.1016/j.nec.2022.08.001 PubMed ↩
4. Chotai S, Nadel JL, Holste KG, et al. Longitudinal scoliosis behavior in Chiari malformation with and without syringomyelia. J Neurosurg Pediatr. 2021;28(5):585-591. doi:10.3171/2021.5.PEDS20915 PubMed ↩
5. Pattisapu JV, Ackerman LL, Infinger LK, et al. Congress of Neurological Surgeons systematic review and evidence-based guidelines for patients with Chiari malformation: surgical interventions. Neurosurgery. 2023;93(4):731-735. doi:10.1227/neu.0000000000002635 Source ↩
6. Hajikarimloo B, Mohammadzadeh I, Habibi MA, et al. Intraoperative ultrasonography in the surgical management of Chiari I malformation: a systematic review and meta-analysis of outcomes and applications. Neurol Sci. 2026;47(4):328. doi:10.1007/s10072-026-08879-8 PubMed ↩
7. Limbrick DD Jr, Shannon CN, Bayman EO, et al; Park-Reeves Syringomyelia Research Consortium Investigators. Decompression with or without duraplasty for Chiari I and syringomyelia. N Engl J Med. 2026;394(20):2015-2025. doi:10.1056/NEJMoa2402821 PubMed ↩
8. Jackson EM, Jernigan S, Raskin JS, et al. Congress of Neurological Surgeons systematic review and evidence-based guidelines for patients with Chiari malformation: symptoms. Neurosurgery. 2023;93(4):727-730. doi:10.1227/neu.0000000000002634 Source ↩
9. Ciaramitaro P, Massimi L, Bertuccio A, et al; International Experts Jury of the Chiari Syringomyelia Consensus Conference. Diagnosis and treatment of Chiari malformation and syringomyelia in adults: international consensus document. Neurol Sci. 2022;43(2):1327-1342. doi:10.1007/s10072-021-05347-3 PubMed ↩

Related pages

• Chiari malformation surgeryChiari decompression surgery: who is offered it, the operation, the evidence on the dural patch and tonsil reduction, results, risks and recovery.
• Symptoms of Chiari malformationChiari malformation symptoms: the cough headache, brainstem and cerebellar symptoms, syrinx symptoms, signs in children and when to get urgent help.
• MRI and diagnosis of Chiari malformationHow Chiari malformation is diagnosed: the MRI criteria, what the millimeters mean, whole-spine imaging, CSF flow studies and conditions that look the same.
• Types of Chiari malformationThe types of Chiari malformation: Chiari 1 and 2, the rare types 3 and 4, borderline Chiari 0 and 1.5, and acquired tonsillar descent.