Syringomyelia & Tethered Cord Syndrome

What is syringomyelia and what is tethered cord?

Two distinct disorders of the spine and spinal cord that are often linked to underlying anatomical abnormalities and require careful evaluation.

Syringomyelia is defined as the formation of an intramedullary, fluid-filled cavity within the spinal cord (a syrinx). It is most commonly located between C2–T9, but may:

• extend toward the brainstem (syringobulbia), or
• extend caudally toward the conus medullaris.

Tethered cord syndrome refers to a clinical condition in which the spinal cord is subjected to pathological traction/tension due to abnormal fixation by an anatomical cause. It is frequently associated with spinal dysraphism and may lead to neurological, orthopedic, and urological dysfunction.

What are the most common causes?

In syringomyelia we primarily investigate causes that disrupt CSF flow. In tethered cord we seek causes of spinal cord fixation or anchoring of the filum terminale.

Causes of syringomyelia

• Arnold–Chiari type I malformation (most common association).
• Craniocervical junction disorders: basilar invagination, os odontoideum, posterior fossa arachnoid cysts.
• Post-traumatic, post-inflammatory, or post-infectious adhesions/arachnoiditis.
• CSF flow obstruction due to arachnoid adhesions, less commonly severe stenosis with flow blockage.
• Association with intramedullary tumors (e.g., ependymoma, hemangioblastoma) – differentiation from cystic tumors is essential.

Causes of tethered cord

• Thickened filum terminale.
• Fatty filum terminale.
• Myelomeningocele or lipomyelomeningocele.
• Split cord malformation (diastematomyelia).
• Dermal sinus tract and other congenital anomalies.
• Intraspinal lipomas or other lesions causing tethering of the spinal cord.

Important: a syrinx of “unknown cause” requires comprehensive diagnostic work-up and contrast-enhanced MRI to exclude an underlying intramedullary tumor.

How does a syrinx form – what does “CSF flow disturbance” mean?

Syringomyelia is frequently linked to obstruction or dysfunction of normal cerebrospinal fluid (CSF) flow and pressure dynamics.

The exact pathophysiology is not fully elucidated. A widely accepted concept proposes that when there is obstruction within the subarachnoid space, the spinal canal cannot normally dissipate CSF pressure waves generated with each cardiac cycle. Elevated pressure proximal to the obstruction may force CSF into the spinal cord, resulting in formation and progressive enlargement of a syrinx.

For this reason, the most effective therapeutic strategy is to restore normal CSF flow wherever it is impaired.

How does a tethered spinal cord cause symptoms?

Under normal conditions, the filum terminale functions as an elastic connective structure. When it loses elasticity or when other tethering lesions or adhesions are present, the spinal cord is subjected to chronic tension.

Increased tension may lead to spinal cord and nerve root dysfunction through:

• mechanical traction on neural structures,
• disturbance of blood supply and microcirculation,
• progressive deterioration during growth, particularly during periods of rapid growth in children.

Therefore, in children, delay or regression of developmental milestones (e.g., walking, bladder control) should always prompt evaluation for underlying pathology.

Which symptoms in syringomyelia should concern you?

Symptoms may result either from the underlying cause (e.g., Chiari I) or from the syrinx itself. Clinical presentation is often asymmetric.

Common clinical features associated with syringomyelia:

• Loss of pain and temperature sensation in a “cape-like” distribution over the shoulders and upper limbs, due to involvement of decussating fibers in the anterior white commissure.
• Weakness/atrophy of the upper limbs (particularly in cervical syringomyelia) from anterior horn involvement.
• Upper motor neuron signs (spasticity, hyperreflexia) when the corticospinal tracts are affected.
• Dysesthesias/neuropathic pain (burning, “electric” sensations), which may be disproportionate to imaging findings.
• Autonomic disturbances such as anhidrosis (reduced sweating) in affected dermatomes.

Important: some patients may have minimal or no symptoms, particularly when the syrinx is small or stable.

Which symptoms in tethered cord should concern you?

Symptoms primarily involve three systems: neurological, orthopedic, and urological. The clinical picture varies with age.

Findings that may be noted on examination

• Cutaneous markers of dysraphism along the midline of the back: dimples/sinuses, dermal sinus tract, hypertrichosis (hair tuft), hemangioma, nevus, lipomatous mass, skin tag.
• Scoliosis or asymmetry of the trunk and limbs.
• Orthopedic deformities: clubfoot, pes cavus, hammertoes, limb-length discrepancy, ankle deformities.

Symptoms by system

• Neurological: low back or leg pain, weakness, sensory deficits, gait disturbance, toe walking (in children), delayed motor milestones.
• Urological: incontinence, urinary frequency, recurrent urinary tract infections, voiding dysfunction. In infants, a “weak urinary stream” may be an indirect sign.
• Orthopedic: progression of scoliosis, limb deformities, pain, and functional limitation.

In children, any regression (e.g., a child who had bladder control and loses it, or who walked normally and develops gait disturbance) warrants urgent evaluation.

How is the diagnosis made – which tests are required?

Accurate diagnosis requires a detailed history, comprehensive neurological examination, and targeted imaging. The clinical evaluation often guides what to specifically assess on MRI.

MRI – the key investigation

• Syringomyelia: MRI of the cervical/thoracic/lumbar spine depending on extent, and often brain and craniocervical junction MRI to evaluate for Chiari malformation or other congenital abnormalities.
• Syrinx of unknown etiology: contrast-enhanced MRI to exclude an intramedullary tumor.
• Tethered cord: thoracolumbar MRI to identify the level of the conus medullaris and evaluate the filum terminale for fatty elements or associated anomalies. In selected cases, supine/prone imaging may be used to assess mobility.

Spinal ultrasound in infants

In infants (approximately up to 3–4 months of age), spinal ultrasound may serve as a useful initial imaging modality, given its ease of performance without sedation or anesthesia.

Urodynamic studies (especially in tethered cord)

Urodynamic testing is particularly valuable for diagnosis and follow-up, often demonstrating: detrusor overactivity, detrusor–sphincter dyssynergia, reduced bladder compliance, or sensory abnormalities.

When is treatment indicated and when is observation appropriate?

The presence of a syrinx or a low-lying conus does NOT automatically mandate surgery. Decisions are based on: symptomatology, progression over time, and identification of a clear underlying etiology.

• Syringomyelia:
  • Active treatment is indicated when a correctable underlying cause is present (e.g., Chiari I) or when progressive neurological deficits occur.
  • Stable, asymptomatic syringomyelia may, in selected cases, be managed with close clinical and MRI surveillance.
• Tethered cord:
  • Symptomatic patients with imaging evidence of tethering generally benefit from microsurgical detethering.
  • Asymptomatic or “borderline” cases require individualized assessment, particularly when symptoms are mild or the conus position is within normal limits.

In children with a history of myelomeningocele, when new concerning symptoms arise, it is critical to first exclude CSF shunt malfunction before attributing findings to “retethering.”

What are the surgical options for syringomyelia?

The primary strategy is treatment of the underlying cause that disrupts normal CSF flow. Direct drainage of the syrinx via shunting is considered a palliative option only when no correctable etiology can be identified or when initial interventions fail.

1) Treatment of the underlying cause

• In Chiari I: craniocervical junction/foramen magnum decompression to restore physiological CSF flow.
• In arachnoid adhesions (post-traumatic/infectious/inflammatory): targeted decompression and lysis of adhesions where obstruction is demonstrated.
• When a tumor is suspected: oncologic management and targeted treatment (approach varies by pathology).

2) Syrinx shunting (selected cases)

Drainage may be directed to:

• the subarachnoid space,
• the posterior fossa cisterns,
• the peritoneal or pleural cavity.

This technique may help halt neurological deterioration, particularly when restoration of normal CSF flow cannot otherwise be achieved.

What are the surgical options for tethered cord?

Treatment is primarily surgical and aims at detethering the spinal cord from pathological fixation while preserving functional neural structures.

Detethering – core principles

• Identification of the cause of tethering (e.g., fatty filum, lipomyelomeningocele, split cord malformation).
• Microsurgical release with meticulous preservation of neural elements and use of intraoperative neuromonitoring.
• For filum sectioning: precise identification (midline/dorsal position, often slightly bluish, especially when fatty), stimulation testing prior to division, and meticulous hemostasis.

Retethering & complex cases

In patients with myelomeningocele or prior surgery, retethering may occur. Re-operations require careful risk–benefit analysis, as scar tissue and adhesions from previous surgery increase the technical complexity of microsurgical detethering. In highly complex cases, specialized strategies (e.g., spinal shortening osteotomy in selected scenarios) may be discussed.

What to expect after treatment – prognosis & follow-up?

The primary goal is to halt progression and, where possible, to improve symptoms. Prognosis depends on symptom duration and the severity of neurological/urological dysfunction prior to treatment.

• Syringomyelia:
  • After successful restoration of CSF flow (e.g., Chiari decompression), the syrinx often gradually regresses.
  • Clinical improvement may be slow, and neuropathic pain does not always fully resolve.
  • Ongoing MRI surveillance and regular neurological assessment are required.
• Tethered cord:
  • In children, early microsurgical detethering can protect development and functional outcomes.
  • Urological dysfunction requires close collaboration with urology and often repeat urodynamic studies.
  • There is a risk of retethering, particularly in complex dysraphic conditions.