Syringomyelia, at its core, is a disorder of an abnormal cerebrospinal fluid (CSF) circulation. A syrinx is a fluid-filled cavity that anatomically lies within the spinal cord parenchyma or the central canal. This entity is most frequently associated with a CM-I, although other known causes include spinal cord tumor, trauma, and post-traumatic or infectious adhesive arachnoiditis. Although syringomyelia predominantly presents with sensory symptoms such as pain and temperature insensitivity, in most cases it is an incidental finding.. The discovery of syringomyelia is becoming more common because of the increased use of MRI in the routine evaluation of back and neck pain.
The natural history of patients with syringomyelia is variable and unpredictable punctuated with periods of stability and progression. Although professionals do not completely understand the natural history of syringomyelia, the clinical course progresses over months to years, with an early rapid deterioration that gradually slows down. It is also understood that sudden jolting of the head, a prolonged bout of coughing may bring a sudden onset of symptoms in a previously asymptomatic patient presumably because of an increase in tonsillar descent.
The etiology of syringomyelia includes conditions that alter the physiologic CSF circulation dynamics. In most cases, it is secondary to spinal subarachnoid space obstruction. Etiology includes
Syrinx in the absence of an identifiable cause
Syringomyelia with obstruction at the foramen magnum (developmental)
Syringomyelia with other diseases of the spinal cord (acquired)
Epidemiological data on syringomyelia is limited. Some studies have found the prevalence of syringomyelia to be from 8.4/100,000 to 0.9/10,000 with ethnic and geographic variation. Majority of the patients present between ages 20 to 50. Familial aggregation, twin studies and known genetic syndromes associated with CM1 and syringomyelia together suggest a genetic component of transmission.
Authors have proposed various theories to explain the origin and progression of syringomyelia.
Although the pathophysiology concerning the origin of syringomyelia remains an elusive Gordian knot, the pathophysiology underpinning progressive syrinx enlargement may have a common theme.
The basic pathology in syringomyelia is a progressively expanding cavity in the central spinal canal. This expanding CSF filled "syrinx" compresses the spinothalamic tract neurons decussating in the anterior white commissure. However, the posterior columns are spared as they are located distally. This results in loss of pain and temperature sensation with preserved touch and vibratory sense (segmental dissociated sensory loss). The upper limbs are preferentially involved in a "cape-like" distribution (sensory loss predominantly in the shoulder area).
Since syringomyelia is commonly associated with Chiari malformation type 1 (CM1), it is pertinent to look at clinical features directly related to Chiari Malformation 1.
Features caused by the syrinx will depend on its anatomical level and include:
The presentation is highly variable. In most cases, patients complain of pain, muscle weakness and atrophy especially in hands and arms, temperature insensitivity in the upper limb, spasticity or stiffness in lower limbs, progressive scoliosis. The clinical course progresses over months to years, with an early rapid deterioration that gradually slows. There is a linear relationship between the cyst morphology, symptom duration, and severity. If there is associated Chiari Malformation 1, patients may also complain of an occipital headache (precipitated by coughing, straining, sneezing, among others), neck pain, gait, and balance problems, dizziness, hoarseness, problems in swallowing, sleep disturbances such as snoring.
In patients with syringomyelia secondary to foramen magnum obstruction treated only a syringosubarachnoid or a thecoperitoneal shunt, it has been observed that the spasticity improves despite the worsening of other neurological functions. This suggests the spasticity in the limbs is possibly due to the bulk of the syrinx rather than the compression of the brainstem at the level of the foramen magnum.
MRI with and without contrast is the investigation of choice. It delineates relevant anatomy and allows accurate visualization of the syrinx in both sagittal and axial planes. MRI easily reveals the location, size, and extent of the syrinx cavity, the degree of cerebellar tonsillar ectopia. A ubiquitous feature in patients with associated CM1 is compression of retro-cerebellar CSF spaces. MRI also helps to rule out cystic lesions or spinal tumors. Leptomeningeal enhancement indicates infection. MRI can also reveal any arachnoid scarring. One can also study syrinx progression over months or years to document the natural history of syringomyelia.
Dynamic MRI or Cardiac Gated CINE-MRI Flow Study
These can analyze CSF hydrodynamics non-invasively. It can diagnose CSF velocity/flow disturbance at foramen magnum (esp. in patients with <5mm tonsillar ectopia), visualize spinal cord wall motion and syrinx fluid motion at rest during the cardiac systole and diastole. It is also useful to document postoperative CSF flow changes and objective improvements.
Myelography with High-Resolution CT Scan
This scan is indicated where MRI cannot be used (patients with metallic implants in the joints, cardiac pacemaker). Delayed CT scans can visualize dye leeched into the syrinx cavity. However, some authors have criticized CT myelography for having a low sensitivity in detecting CSF blockage.
Electromyography has no diagnostic value in syringomyelia, but it helps to rule out peripheral neuropathy causing paresthesias.
The goal of treatment is to correct the underlying causative pathophysiology. All current treatment strategies are directed toward improving CSF flow dynamics.
In patients with Chiari malformation 1, craniocervical decompression is the best way forward. This consists of suboccipital craniectomy and removal of the posterior arch of C1, opening the dura and arachnoid, and resection of arachnoid adherences when present. What this surgery essentially does is that it creates an artificially enlarged cisterna magna. Intraoperative ultrasonography can be employed to confirm the decompression of the tonsil and pulsatile flow of the cerebrospinal fluid around the craniovertebral junction. The duration of sensory deficits best predicts the symptomatic improvement following surgery. Studies have shown that shorter duration of the preoperative symptoms has better outcomes. Early surgery minimizes deficits.
In the patients with post-inflammatory arachnoid scarring and post-traumatic syringomyelia, the operative procedure is directed toward reconstituting spinal subarachnoid CSF flow by arachnoid scar membrane resection, microsurgical lysis of arachnoid adherences and dural reconstruction.
Shunts are indicated for idiopathic syringomyelia and patients that have not responded to other treatment. Most commonly used is syringosubarachnoid shunt (SSAS). If this fails syringoperitoneal shunt (SPS) may be used. While there are studies that claim to have better outcomes with SSAS as compared to foramen magnum decompression, this thought is not universally echoed. In most cases, shunts are not favored and are used as a last resort because of high complication and failure rates, and inability to resolve the underlying etiology.
Professionals still do not understand the natural history of syringomyelia; it is unpredictable and highly variable which makes its prognostication very difficult. Although prognosis depends on the etiology, the degree of neurological deficit and the site and size of the syrinx cavity, syrinx diameter of more than 5 mm and associated edema predict a rapid deterioration. The rarity of the condition, variable natural history, and short follow-up make treatment results assessment difficult. However, early surgery minimizes deficits and has better outcomes.
Myelopathy is the major complications because of the disease process itself. This can further lead to spasticity which may progress to paraplegia/quadriplegia, decubitus ulcers, recurrent pneumonia, and bowel and bladder dysfunction.
Neurological complications following surgery include cerebrospinal fluid (CSF) leaks, infection, hemorrhage, recurrence of the syrinx.
Identifying and distinguishing the root cause of deficits in post-traumatic syringomyelia, the syrinx cavity or cord injury itself, remains a challenge.
Post-operative pain is a major issue for patients and is often managed with opioids and muscle relaxants. It is important that the patient and his/her family understand that their physicians cannot overmedicate. Pain medications are a double-edged sword. The risk/benefit ratio must be weighed carefully. Oversedation with opioids may put the patient at risk for developing complications such as pneumonia. The physician must carefully titrate the dose of pain medications to allow maximum comfort with minimum risk of complications for the patient. It is crucial that the patient, family, and friends comprehend and respect this balancing act. A well-informed patient can assist their physician in the process by comprehending the proposed strategy for the diagnosis, workup and subsequent treatment.
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