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Summary Table

Category	Detail
Risk Factors	Chiari I malformation (most common association), history of spinal cord trauma, spinal cord tumors (intramedullary), prior meningitis, tethered cord
Etiology	Formation of a fluid-filled cavity (syrinx) within the central spinal cord, most often in the cervical region, disrupting neural pathways as it expands
Patient Presentation	Young adult presenting with bilateral loss of pain and temperature sensation in the upper extremities and trunk ("cape-like" distribution), with preserved light touch. Often reports painless burns or injuries to the hands
Classic Physical Exam	Dissociated sensory loss (pain/temperature lost, light touch/proprioception preserved), hand intrinsic muscle atrophy, absent upper extremity reflexes (LMN at the level), hyperreflexia in lower extremities (UMN below the level), possible Horner syndrome
Key Diagnostic Results	MRI of the spine showing a fluid-filled cavity (syrinx) within the spinal cord; MRI of the brain may reveal tonsillar herniation (Chiari I malformation)
Management	Observation if stable and asymptomatic. Posterior fossa decompression surgery for Chiari-associated syringomyelia with progressive neurological deficits. Syringoperitoneal or syringosubarachnoid shunt if decompression fails
Keywords	"Cape-like sensory loss," "dissociated sensory loss," "painless burns on hands," "loss of pain/temperature with preserved touch," "Chiari malformation," "central cord cavity"

1. Pathophysiology

Syringomyelia refers to the development of a syrinx, a longitudinal fluid-filled cavity that forms within the substance of the spinal cord, most frequently in the cervical and upper thoracic segments. The most common underlying cause is Chiari I malformation, in which the cerebellar tonsils herniate more than 5 mm below the foramen magnum. This herniation obstructs the normal flow of cerebrospinal fluid (CSF) at the craniocervical junction. Over time, the altered CSF dynamics create a pressure gradient that forces fluid into the central canal of the spinal cord, leading to progressive cavitation.

The reason this disease produces such a distinctive clinical pattern lies in the anatomy of the spinal cord cross-section. The syrinx begins in the central region of the cord, where it first disrupts the anterior white commissure. This is the structure where second-order spinothalamic neurons cross from one side to the other before ascending. Because these fibers carry pain and temperature information, bilateral destruction of the crossing fibers produces the classic finding: loss of pain and temperature sensation in a dermatomal band across the shoulders, arms, and upper trunk, while light touch and proprioception (carried by the dorsal columns, which are located posteriorly) remain intact. This selective pattern is called dissociated sensory loss, and it is the hallmark feature tested on exams.

As the syrinx enlarges, it expands outward and begins to involve adjacent structures. Anterior horn cell destruction at the level of the lesion produces lower motor neuron (LMN) signs in the upper extremities, including muscle wasting, weakness, fasciculations, and decreased reflexes, particularly in the hand intrinsics (thenar and hypothenar muscles). If the cavity extends laterally into the lateral corticospinal tracts, upper motor neuron (UMN) signs appear in the lower extremities, including spasticity, hyperreflexia, and extensor plantar responses (Babinski sign). In cervicothoracic syrinxes, disruption of the ciliospinal center of Budge (C8-T2) can interrupt the sympathetic chain, producing an ipsilateral Horner syndrome (ptosis, miosis, anhidrosis).

The key concept for exam purposes is that syringomyelia produces a "central cord" pattern that evolves from the inside out: crossing spinothalamic fibers first, then anterior horn cells, then corticospinal tracts, and finally dorsal columns (a late and uncommon finding).

2. Classification and Clinical Manifestation

By Etiology

Type	Description
Communicating syringomyelia	Syrinx communicates with the fourth ventricle; associated with Chiari malformations, Dandy-Walker malformation, or basilar arachnoiditis
Non-communicating syringomyelia	Syrinx does not communicate with the fourth ventricle; caused by spinal cord trauma, intramedullary tumors (e.g., ependymoma, hemangioblastoma), arachnoiditis, or tethered cord
Idiopathic	No identifiable cause found on imaging

By Stage of Expansion

Structure	Clinical Finding	Motor Neuron Type	Exam Clue
Anterior white commissure (earliest)	Bilateral suspended dissociated sensory loss: loss of pain and temperature in a "cape-like" distribution; light touch and proprioception preserved	N/A (sensory tract)	"Patient cannot feel burns on hands but can feel light touch"
Anterior horn cells	Weakness and atrophy of hand intrinsic muscles, fasciculations, decreased reflexes in upper extremities	LMN at the level of the lesion	"Wasting of hand muscles," "claw hand," "absent biceps reflex"
Lateral corticospinal tract	Spastic paraparesis of lower extremities, hyperreflexia, Babinski sign	UMN below the level of the lesion	"Stiff legs," "increased knee jerk," "upgoing toes"
Intermediolateral cell column (C8-T2)	Ipsilateral Horner syndrome (ptosis, miosis, anhidrosis)	Sympathetic preganglionic neurons	"Unilateral small pupil with drooping eyelid"
Dorsal columns (late)	Loss of proprioception and vibration (uncommon, seen only with large syrinxes)	N/A (sensory tract)	Rarely tested; if present, suggests very advanced disease

3. Diagnostic Workup

Test	Role	Key Findings
MRI of the spine (with and without contrast)	Best initial test AND gold standard	Fluid-filled cavity (syrinx) within the spinal cord parenchyma, typically cervicothoracic; contrast helps exclude intramedullary tumor
MRI of the brain (with craniocervical junction)	Evaluate for underlying cause	Cerebellar tonsillar herniation greater than 5 mm below foramen magnum (Chiari I); posterior fossa crowding
CSF flow study (cine MRI)	Assess CSF dynamics at the foramen magnum	Obstruction of CSF flow at the craniocervical junction; helps guide surgical planning
Electromyography (EMG) / Nerve Conduction Studies	Supportive, not diagnostic	Evidence of denervation in upper extremity muscles (anterior horn cell involvement); helps differentiate from peripheral neuropathy

The best initial test is an MRI of the entire spine. This is also the most accurate (confirmatory) test. On T2-weighted images, the syrinx appears as a well-defined, hyperintense, longitudinal cavity within the spinal cord that follows CSF signal intensity. The T1-weighted sequence will show the cavity as hypointense. Gadolinium contrast is added to rule out an enhancing intramedullary tumor (such as ependymoma or hemangioblastoma) as the cause of the syrinx, since tumors enhance while a simple syrinx does not.

Once a syrinx is identified, the next step is to determine the underlying etiology. An MRI of the brain including the craniocervical junction is ordered to evaluate for Chiari I malformation. The hallmark finding is cerebellar tonsils descending more than 5 mm below the foramen magnum on sagittal imaging.

A cine-phase contrast MRI (CSF flow study) can be performed preoperatively. This dynamic study evaluates CSF flow at the foramen magnum and is helpful in surgical planning, demonstrating whether there is a flow obstruction that would benefit from decompression.

EMG and nerve conduction studies are not required for diagnosis but can be useful when the clinical picture is unclear, as they can confirm anterior horn cell involvement and help distinguish syringomyelia from conditions such as cervical radiculopathy, carpal tunnel syndrome, or amyotrophic lateral sclerosis.

A critical exam point: a syrinx that is identified incidentally on MRI does not always require treatment. Small, stable, asymptomatic syrinxes can be monitored with serial imaging.

4. Management and Treatment

Scenario	Management	Details
Asymptomatic or stable syrinx	Observation with serial MRI	Repeat MRI every 6 to 12 months initially, then annually if stable
Chiari I with progressive symptoms	Posterior fossa decompression (suboccipital craniectomy with C1 laminectomy and duraplasty)	First-line surgical treatment; addresses the underlying obstruction
Syrinx persists or progresses after decompression	Syrinx shunting (syringoperitoneal or syringosubarachnoid shunt)	Second-line; used when decompression alone does not resolve the cavity
Tumor-associated syrinx	Tumor resection	Removing the tumor typically resolves the syrinx
Post-traumatic syringomyelia	Surgical untethering or shunting	Directed at relieving tethering and restoring CSF flow
Pain management	Gabapentin or pregabalin for neuropathic pain; NSAIDs or acetaminophen for musculoskeletal pain	Neuropathic pain is common and can persist even after surgery

Step 1: Confirm diagnosis and identify the cause. Once MRI confirms the syrinx, the underlying etiology dictates the treatment plan. The most common testable scenario is a syrinx secondary to Chiari I malformation.

Step 2: Observation vs. intervention. If the patient is asymptomatic and the syrinx is discovered incidentally, the appropriate next step is clinical and radiographic surveillance. Serial MRI is performed every 6 to 12 months initially. Surgery is reserved for patients with progressive neurological deficits, worsening syrinx size on imaging, or debilitating symptoms.

Step 3: Surgical treatment for Chiari-associated syringomyelia. The first-line surgical intervention is posterior fossa decompression, which involves a suboccipital craniectomy, C1 (and sometimes C2) laminectomy, and duraplasty. This procedure restores normal CSF circulation at the craniocervical junction, which in the majority of patients leads to stabilization or reduction of the syrinx. The goal is to address the obstruction causing the syrinx, not to drain the syrinx directly.

Step 4: Refractory cases. If neurological deterioration continues or the syrinx does not decrease in size after posterior fossa decompression, a syringosubarachnoid or syringoperitoneal shunt may be placed. However, shunts carry risks of obstruction, infection, and recurrence, so they are considered second-line.

Step 5: Address associated conditions. In tumor-related syringomyelia, the treatment is resection of the intramedullary tumor. In post-traumatic cases, surgical lysis of adhesions or untethering may be necessary. Arachnoiditis-related syrinxes are challenging and may require shunting.

Step 6: Symptomatic management. Neuropathic pain is treated with gabapentin (starting at 300 mg daily, titrated up to 3600 mg/day in divided doses) or pregabalin (starting at 75 mg twice daily, up to 300 mg twice daily). Physical therapy and occupational therapy are important adjuncts for patients with motor deficits. Patients should be counseled to avoid activities that increase intrathoracic pressure (heavy lifting, straining, Valsalva maneuver), as these can worsen the syrinx.

Contraindications and cautions: Lumbar puncture should be performed with caution in patients with Chiari malformation due to the risk of tonsillar herniation. In patients with known Chiari I, a brain MRI should always be reviewed before any LP.

5. Differential Diagnosis and Distractors

Differential	Why It Is Similar	Key Discriminator
Multiple Sclerosis (MS)	Can cause spinal cord symptoms (weakness, sensory changes, spasticity) in a young adult	MS produces patchy, asymmetric deficits with relapsing-remitting course; MRI shows demyelinating plaques, not a central fluid-filled cavity. MS does NOT produce dissociated sensory loss in a cape-like distribution
Amyotrophic Lateral Sclerosis (ALS)	Presents with combined UMN and LMN signs, hand muscle wasting	ALS is purely motor; there is no sensory involvement. If the vignette mentions any sensory loss, ALS is ruled out
Cervical spondylotic myelopathy	Can produce upper extremity LMN signs and lower extremity UMN signs (similar "mixed" pattern)	Usually affects older patients (>50); MRI shows disc/osteophyte compression of the cord externally, NOT an intramedullary cavity. Sensory loss follows radicular dermatomes, not a suspended cape-like pattern
Subacute combined degeneration (B12 deficiency)	Causes dorsal column dysfunction and corticospinal tract signs	B12 deficiency primarily affects dorsal columns (loss of vibration and proprioception), which is the opposite of syringomyelia's early presentation. Megaloblastic anemia and elevated methylmalonic acid point to B12 deficiency
Intramedullary spinal cord tumor (ependymoma, astrocytoma)	Can present identically to syringomyelia (the tumor itself can produce a syrinx)	MRI with contrast is the discriminator: tumors enhance with gadolinium, while a simple syrinx does not. The presence of an enhancing mass within the cord changes the diagnosis and management entirely
Brown-Sequard syndrome (cord hemisection)	Produces dissociated sensory findings	Brown-Sequard is unilateral: ipsilateral motor loss and dorsal column loss with contralateral spinothalamic loss. Syringomyelia is bilateral and symmetric. History of penetrating trauma or lateral cord lesion is the clue
Peripheral neuropathy (e.g., carpal tunnel, ulnar neuropathy)	Hand weakness and numbness can mimic early syringomyelia	Peripheral neuropathies follow a nerve distribution (median, ulnar), not a suspended dermatomal band. Nerve conduction studies will localize the lesion to a peripheral nerve, not the spinal cord

6. Traps and High-Yield Pearls

The most common way students get questions about syringomyelia wrong is by failing to recognize the dissociated sensory loss pattern. When a vignette describes a young patient with bilateral loss of pain and temperature in the upper extremities but preserved light touch, many students default to diagnoses like MS, cervical radiculopathy, or peripheral neuropathy. The key is recognizing that selective loss of pain and temperature with intact light touch and proprioception points to disruption of crossing spinothalamic fibers, and the bilateral, suspended, cape-like distribution is the signature of a central cord process.

A second common trap is confusing syringomyelia with an intramedullary tumor. Both can look alike clinically and even on initial MRI sequences. The vignette will often include the detail that the lesion "follows CSF signal on all sequences" and "does not enhance with gadolinium." If the lesion enhances, think tumor. If it does not, think syrinx.

Students also frequently miss the Chiari I connection. When a question describes a patient with occipital headaches worsened by coughing or straining, combined with the cape-like sensory loss, the expected answer links the syrinx to Chiari I malformation, and the appropriate management is posterior fossa decompression rather than direct drainage of the syrinx.

Another testable pearl: the "painless burn" clue. Vignettes may describe a patient who repeatedly injures or burns their hands without feeling pain. This is a classic setup for syringomyelia, and it tests whether you understand that pain fibers are selectively lost while tactile sensation remains.

Finally, remember the motor pattern: LMN signs in the upper extremities (atrophy, weakness, decreased reflexes) combined with UMN signs in the lower extremities (spasticity, hyperreflexia, Babinski) is the hallmark of a cervical spinal cord lesion expanding from the center outward. This combination of LMN-at-the-level and UMN-below-the-level is heavily tested and should immediately prompt consideration of syringomyelia or a central cord process.

The core competency being tested is the ability to localize the lesion to the central spinal cord based on the pattern of neurological deficits, connect that localization to the correct diagnosis, identify the underlying cause, and select the appropriate management sequence.

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