Syringomyelia

Article Author:
Varadaraya Satyanarayan Shenoy
Article Editor:
Raghuram Sampath
Updated:
3/19/2019 12:25:40 AM
PubMed Link:
Syringomyelia

Introduction

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[1]. This entity is most frequently associated with a CM-I,[2] although other known causes include spinal cord tumor, trauma, and post-traumatic or infectious adhesive arachnoiditis.[3][4] Although syringomyelia predominantly presents with sensory symptoms such as pain and temperature insensitivity, in most cases it is an incidental finding.[1][5]. The discovery of syringomyelia is becoming more common because of the increased use of MRI in the routine evaluation of back and neck pain.[5]

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.[6] 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.[2][7]

Syringomyelia accounts for up to 5% of paraplegias.[8] The quality of life in syringomyelia patients is comparable with that of patients with heart failure or malignant neoplasms.[9]

Etiology

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

Idiopathic Syringomyelia 

Syrinx in the absence of an identifiable cause

Secondary Syringomyelia 

Syringomyelia with obstruction at the foramen magnum (developmental)

  • Chiari 1 Malformation (CM1): Most common association[2]
  • Basilar invagination

Syringomyelia with other diseases of the spinal cord (acquired)

  • Post-inflammatory
    • Post-infectious: Granulomatous (tuberculosis, fungal), post-operative meningitis
    • Chemical/ Sterile inflammation: Post-subarachnoid hemorrhage (SAH), post-myelography (metrizamide)
  • Post-traumatic
  • Spinal Cord Tumors: Intra-medullary spinal tumors esp. Hemangioblastoma 
  • Secondary myelomalacia: Cord compression (herniated disc, spondylosis, tumors), infarction, hematomyelia

Epidemiology

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.[10][11] 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.[2][12]

Pathophysiology

Authors have proposed various theories to explain the origin and progression of syringomyelia. 

  • Gardner and Angel publicized the "hydrodynamic theory." Hindbrain hernias obstruct the normal CSF egress. Therefore, the fluid swerves into the central spinal canal pulsating into the central spinal canal with each heartbeat ("water-hammer" effect).[13]
  • Williams found pressure gradients of over 100 mg Hg across foramen magnum during Valsalva maneuvers in hindbrain hernia patients and postulated that this cranial spatial pressure differential creates a suctional force ("suck") that pulls the ventricular CSF into the syrinx. The fluid drawn into the cavity would then impact-and-bounce off ("slosh") the caudal and subsequently rostral walls of the syrinx,[14][15] similar to the behavior of water in an elastic balloon squeezed at one end. This theory was no longer in vogue after subsequent authors underscored the lack of communication between syrinx and the fourth ventricle.[16][17] However, recently this theory has found evidentiary support on dynamic MRI studies. Slow caudal growth of a syrinx may follow 42 million such impacts during a year.[18]
  • Ball and Dayan argued that CSF drives through the spinal cord surface along para-vascular Virchow-robin spaces because of increased spinal CSF pressure (coughing, sneezing) in patients with foramen magnum obstruction.[19]
  • However, there are no compelling large-scale physiological studies to refute or confirm any of these three proposals.[20]
  • Oldfield et al. proposed that a CSF pressure wave generated because of systolic "piston-like" caudal displacement of tonsils, contracted the cord forcing fluid into the syrinx cavity from the spinal subarachnoid space.[16] However, a critique is that fluid cannot enter a contracted cord. While studies have been able to show a downward movement of the tonsils during systole on dynamic MRI, there has been no visual confirmation of trans-parenchymal CSF movement on CINE MRI.[18]
  • Gretiz[1] and Koyanagi and Houkinkoya[21] have proposed a theory supporting extracellular nature of syrinx fluid rather than CSF. Abnormally rapid movement of CSF past the cord causes a low-pressure zone within the cord, promoting extracellular fluid build-up and syrinx formation.[18]

Although the pathophysiology concerning the origin of syringomyelia remains an elusive Gordian knot, the pathophysiology underpinning progressive syrinx enlargement may have a common theme.[18]

Clinicopathological Correlation

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).

History and Physical

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.

  1. Tussive headaches: Classic of CM1. Coughing (Valsalva maneuvers) causes sudden increases in intracranial CSF volume in CM1 patients which presents as transient suboccipital headache and neck pain, a split second after a cough.[2] It is important to understand the features of Chiari headaches to prevent misdiagnoses 
    • Site: Sub-occipital
    • Mode of onset: Sudden 
    • Nature/character: Heavy, crushing, pressure-like. Pounding in quality when severe but otherwise non-throbbing[2]
    • Radiation: Radiates to the vertex and behind the eyes, and inferiorly to the neck and shoulders
    • Duration: Short duration-often, lasting only seconds
    • Exacerbated by physical exertion, Valsalva maneuvers, head dependency, sudden changes in posture
  2. Hoarseness, dysphagia, coughing with swallowing because of downward traction on the lower cranial nerves and brainstem compression.
  3. Visual disturbances: Retro-orbital pressure and pain, visual phenomena such as flashing lights, floaters, blurred vision, photophobia, diplopia; possible horizontal, rotatory or down-beat nystagmus on clinical examination because of the involvement of brainstem vestibulo-ocular connections
  4. Oto-neurologic symptoms: Dizziness, tinnitus, pressure in ears, decreased hearing, oscillopsia
  5. Cerebellar disturbances such as tremors, dysmetria, ataxia, gait and balance problems.
  6. Syncope[22]
  7. Sleep disturbances such as snoring, sleep apnea and palpitations because of brainstem compression

Features caused by the syrinx will depend on its anatomical level and include:

  1. The most common sensory symptom is paresthesia/hyperesthesia followed by non-radicular segmental pain.[2] 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. Due to the lack of pain perception, patients often develop injuries, chronic skin ulcerations on the hand.
  2. Muscle weakness, impaired fine-motor function which may progress to atrophy of intrinsic muscles of hand – damage to the anterior horn cells (lower motor neuron) at the level of the syrinx. May progress to "claw hand" deformity.
  3. Spasticity in lower limbs: Syrinx expansion may compress and sometimes destruct adjacent lateral corticospinal tracts (upper motor neuron).
  4. Progressive scoliosis: Injury to anterior horn cells innervating the paraspinal axial musculature[23]
  5. Horner syndrome may be seen in cervical/upper thoracic syringes
  6. Poorly localized non-radicular segmental neuropathic pain (substance P)[24]

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.[6] There is a linear relationship between the cyst morphology, symptom duration, and severity.[25][26] 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.[27]

Evaluation

MRI

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.[2][18] 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.[28]

Electromyography has no diagnostic value in syringomyelia, but it helps to rule out peripheral neuropathy causing paresthesias.

Treatment / Management

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.[3] 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.[29] 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.[30]

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.[30][31]

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,[32] this thought is not universally echoed.[26][33] 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. 

Differential Diagnosis

  1. Spinal intra-medullary tumors such as hemangioblastoma, ependymoma, gliomas: Tumors may secrete exudative fluid (high in protein content) causing micro-cysts that can eventually coalesce. Most of these intramedullary tumors will enhance on contrast MRI (a syrinx does not enhance on contrast MRI). However, a true syrinx can occur within a tumor)
  2. Spinal intra-medullary cysts
  3. Myelomalacia
  4. Arachnoid cysts
  5. Glio-ependymal cysts
  6. Residual central spinal canal: The central canal of the spinal cord involutes with age. A persistent central canal is NOT an anomaly. 

Prognosis

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.[34] However, early surgery minimizes deficits and has better outcomes.

Complications

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.[35]

Neurological complications following surgery include cerebrospinal fluid (CSF) leaks, infection, hemorrhage, recurrence of the syrinx.

Deterrence and Patient Education

  1. Patients with untreated syringomyelia should avoid straining during bowel movements (especially in the initial weeks after surgery, when they may be on narcotic pain medication which often causes constipation) coughing, sneezing which can worsen symptoms and further enlarge the syrinx. Patients must consult the doctor when symptomatic for a cough or constipation 
  2. Similarly, patients with syringomyelia should avoid lifting heavy weights.
  3. Experts advise patients with Chiari malformation to avoid activities that exert significant strain to the neck such as roller coasters, trampolines. Patients should avoid contact sports such as football. They may practice alternative forms of exercise such as swimming, stationary bicycling, and yoga.
  4. The patient must immediately report any post-operatively drainage of purulent fluid from the surgical site or signs of infection, such as a painful, edematous, reddened wound, to the treating physician.

Pearls and Other Issues

  1. Syringomyelia(SM) should be considered high in the differential diagnosis in any young person with progressive scoliosis. Early identification and treatment can cause a reversal of deformity.[36] 
  2. Hand involvement in syringomyelia patients is often asymmetric as syrinx cavity itself is eccentric in most cases.
  3. It is important for clinicians to distinguish Chiari headaches from other similar appearing headaches. History taking skills play a crucial role.
    • History of a long duration of a headache and pain relief by neck support can help in identifying headaches originating in neck muscles that may extend into the suboccipital area.
    • Posterior fossa brain tumors may produce similar headaches and also cause tonsillar descent. However, these headaches are of prolonged duration and have associated projectile vomiting. Fundoscopy in these patients may also reveal papilledema.
    • Headaches in fibromyalgia patients may also mimic Chiari headaches.[37]
  4. Being a chronic disorder, a patient with syringomyelia not uncommonly has symptoms of anxiety, memory impairment, depression. The clinician is obligated to assess all symptoms with the right perspective, particularly the possibility of a specific symptom being mitigated by surgery. The wide availability of symptom lists on the internet, some which are non-specific adds to the challenge of eliciting an uncontaminated history from the patient.[38]

Challenges/Pitfalls

Identifying and distinguishing the root cause of deficits in post-traumatic syringomyelia, the syrinx cavity or cord injury itself, remains a challenge.

Enhancing Healthcare Team Outcomes

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.



  • (Move Mouse on Image to Enlarge)
    • Image 7390 Not availableImage 7390 Not available
      Contributed by Dr Varadaraya Shenoy, MBBS

References

[1] Greitz D, Unraveling the riddle of syringomyelia. Neurosurgical review. 2006 Oct;     [PubMed PMID: 16752160]
[2] Milhorat TH,Chou MW,Trinidad EM,Kula RW,Mandell M,Wolpert C,Speer MC, Chiari I malformation redefined: clinical and radiographic findings for 364 symptomatic patients. Neurosurgery. 1999 May;     [PubMed PMID: 10232534]
[3] Roy AK,Slimack NP,Ganju A, Idiopathic syringomyelia: retrospective case series, comprehensive review, and update on management. Neurosurgical focus. 2011 Dec;     [PubMed PMID: 22133183]
[4] Klekamp J,Batzdorf U,Samii M,Bothe HW, Treatment of syringomyelia associated with arachnoid scarring caused by arachnoiditis or trauma. Journal of neurosurgery. 1997 Feb;     [PubMed PMID: 9010425]
[5] Roser F,Ebner FH,Sixt C,Hagen JM,Tatagiba MS, Defining the line between hydromyelia and syringomyelia. A differentiation is possible based on electrophysiological and magnetic resonance imaging studies. Acta neurochirurgica. 2010 Feb;     [PubMed PMID: 19533016]
[6] Bogdanov EI,Mendelevich EG, Syrinx size and duration of symptoms predict the pace of progressive myelopathy: retrospective analysis of 103 unoperated cases with craniocervical junction malformations and syringomyelia. Clinical neurology and neurosurgery. 2002 May;     [PubMed PMID: 11932037]
[7] Mampalam TJ,Andrews BT,Gelb D,Ferriero D,Pitts LH, Presentation of type I Chiari malformation after head trauma. Neurosurgery. 1988 Dec;     [PubMed PMID: 3216976]
[8] Williams B, Post-traumatic syringomyelia, an update. Paraplegia. 1990 Jun     [PubMed PMID: 2235038]
[9] Sixt C,Riether F,Will BE,Tatagiba MS,Roser F, Evaluation of quality of life parameters in patients who have syringomyelia. Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia. 2009 Dec     [PubMed PMID: 19818628]
[10] Weier K,Naegelin Y,Thoeni A,Hirsch JG,Kappos L,Steinbrich W,Radue EW,Gass A, Non-communicating syringomyelia: a feature of spinal cord involvement in multiple sclerosis. Brain : a journal of neurology. 2008 Jul;     [PubMed PMID: 18515871]
[11] Brickell KL,Anderson NE,Charleston AJ,Hope JK,Bok AP,Barber PA, Ethnic differences in syringomyelia in New Zealand. Journal of neurology, neurosurgery, and psychiatry. 2006 Aug;     [PubMed PMID: 16549414]
[12] Speer MC,Enterline DS,Mehltretter L,Hammock P,Joseph J,Dickerson M,Ellenbogen RG,Milhorat TH,Hauser MA,George TM, Review Article: Chiari Type I Malformation with or Without Syringomyelia: Prevalence and Genetics. Journal of genetic counseling. 2003 Aug;     [PubMed PMID: 26141174]
[13] GARDNER WJ,ANGEL J, The mechanism of syringomyelia and its surgical correction. Clinical neurosurgery. 1958;     [PubMed PMID: 13826542]
[14] Williams B, Pathogenesis of syringomyelia. Lancet (London, England). 1972 Nov 4;     [PubMed PMID: 4116840]
[15] Williams B, On the pathogenesis of syringomyelia: a review. Journal of the Royal Society of Medicine. 1980 Nov;     [PubMed PMID: 7017117]
[16] Oldfield EH,Muraszko K,Shawker TH,Patronas NJ, Pathophysiology of syringomyelia associated with Chiari I malformation of the cerebellar tonsils. Implications for diagnosis and treatment. Journal of neurosurgery. 1994 Jan;     [PubMed PMID: 8271018]
[17] Milhorat TH,Miller JI,Johnson WD,Adler DE,Heger IM, Anatomical basis of syringomyelia occurring with hindbrain lesions. Neurosurgery. 1993 May;     [PubMed PMID: 8492850]
[18] Honey CM,Martin KW,Heran MKS, Syringomyelia Fluid Dynamics and Cord Motion Revealed by Serendipitous Null Point Artifacts during Cine MRI. AJNR. American journal of neuroradiology. 2017 Sep;     [PubMed PMID: 28751514]
[19] Ball MJ,Dayan AD, Pathogenesis of syringomyelia. Lancet (London, England). 1972 Oct 14;     [PubMed PMID: 4116236]
[20] Oldfield EH, Pathogenesis of Chiari I - Pathophysiology of Syringomyelia: Implications for Therapy: A Summary of 3 Decades of Clinical Research. Neurosurgery. 2017 Sep 1;     [PubMed PMID: 28899066]
[21] Koyanagi I,Houkin K, Pathogenesis of syringomyelia associated with Chiari type 1 malformation: review of evidences and proposal of a new hypothesis. Neurosurgical review. 2010 Jul;     [PubMed PMID: 20532585]
[22] Weig SG,Buckthal PE,Choi SK,Zellem RT, Recurrent syncope as the presenting symptom of Arnold-Chiari malformation. Neurology. 1991 Oct;     [PubMed PMID: 1922816]
[23] Batzdorf U,Khoo LT,McArthur DL, Observations on spine deformity and syringomyelia. Neurosurgery. 2007 Aug;     [PubMed PMID: 17762750]
[24] Milhorat TH,Mu HT,LaMotte CC,Milhorat AT, Distribution of substance P in the spinal cord of patients with syringomyelia. Journal of neurosurgery. 1996 Jun;     [PubMed PMID: 8847594]
[25] Grant R,Hadley DM,Macpherson P,Condon B,Patterson J,Bone I,Teasdale GN, Syringomyelia: cyst measurement by magnetic resonance imaging and comparison with symptoms, signs and disability. Journal of neurology, neurosurgery, and psychiatry. 1987 Aug;     [PubMed PMID: 3655805]
[26] Fujii K,Natori Y,Nakagaki H,Fukui M, Management of syringomyelia associated with Chiari malformation: comparative study of syrinx size and symptoms by magnetic resonance imaging. Surgical neurology. 1991 Oct;     [PubMed PMID: 1948628]
[27] Goel A,Desai K, Surgery for syringomyelia: an analysis based on 163 surgical cases. Acta neurochirurgica. 2000;     [PubMed PMID: 10819260]
[28] Mauer UM,Freude G,Danz B,Kunz U, Cardiac-gated phase-contrast magnetic resonance imaging of cerebrospinal fluid flow in the diagnosis of idiopathic syringomyelia. Neurosurgery. 2008 Dec;     [PubMed PMID: 19057326]
[29] Dyste GN,Menezes AH,VanGilder JC, Symptomatic Chiari malformations. An analysis of presentation, management, and long-term outcome. Journal of neurosurgery. 1989 Aug;     [PubMed PMID: 2746341]
[30] Attal N,Parker F,Tadié M,Aghakani N,Bouhassira D, Effects of surgery on the sensory deficits of syringomyelia and predictors of outcome: a long term prospective study. Journal of neurology, neurosurgery, and psychiatry. 2004 Jul;     [PubMed PMID: 15201364]
[31] Lee TT,Alameda GJ,Camilo E,Green BA, Surgical treatment of post-traumatic myelopathy associated with syringomyelia. Spine. 2001 Dec 15;     [PubMed PMID: 11805618]
[32] Hida K,Iwasaki Y,Koyanagi I,Sawamura Y,Abe H, Surgical indication and results of foramen magnum decompression versus syringosubarachnoid shunting for syringomyelia associated with Chiari I malformation. Neurosurgery. 1995 Oct;     [PubMed PMID: 8559295]
[33] Grant R,Hadley DM,Lang D,Condon B,Johnston R,Bone I,Teasdale GM, MRI measurement of syrinx size before and after operation. Journal of neurology, neurosurgery, and psychiatry. 1987 Dec;     [PubMed PMID: 3437304]
[34] Logue V,Edwards MR, Syringomyelia and its surgical treatment--an analysis of 75 patients. Journal of neurology, neurosurgery, and psychiatry. 1981 Apr;     [PubMed PMID: 7241155]
[35] Bleck TP,Shannon KM, Disordered swallowing due to a syrinx: correction by shunting. Neurology. 1984 Nov;     [PubMed PMID: 6493500]
[36] Muhonen MG,Menezes AH,Sawin PD,Weinstein SL, Scoliosis in pediatric Chiari malformations without myelodysplasia. Journal of neurosurgery. 1992 Jul;     [PubMed PMID: 1607974]
[37] Watson NF,Buchwald D,Goldberg J,Maravilla KR,Noonan C,Guan Q,Ellenbogen RG, Is Chiari I malformation associated with fibromyalgia? Neurosurgery. 2011 Feb;     [PubMed PMID: 21135714]
[38] Mueller DM,Oro' JJ, Prospective analysis of presenting symptoms among 265 patients with radiographic evidence of Chiari malformation type I with or without syringomyelia. Journal of the American Academy of Nurse Practitioners. 2004 Mar;     [PubMed PMID: 15130068]