Syringomyelia

Chiari-‐like Malforma/on/ 

Syringomyelia 

Daniel R James BVSc (Hons) MANZCVS (Radiology/ Surgery) 

Resident in Small Animal Surgery

Syringomyelia 

• Defini/ons-‐Syringo V hydro 

» Ependymal lining 

» Communica/ng 

» No Arnold 

» Chiari-‐LIKE

Clinical signs: 

• Usually recognized between 6m and 3yr old 

• Owners reported increased signs during 

exer/on, barking, or when excited. 

– thought that rapid changes in intrathoracic or 

intra-‐abdominal pressure are important


• Characteris/c scratching at neck, 

shoulder, flank, ear or sternum. 

-‐ especially when walking 

-‐Typically unilateral 

-‐ “Phantom” scratching or “Air 

Guitar”


• Scratching neck, shoulder, flank, ear or sternum. 

• Neuropathic pain 

-‐Spinal pain, especially neck pain. 

-‐may be episodic and o\en severe. 

-‐May be worse when head is lowered 

-‐Head ache*, radicular pain, allodynia 

dysaesthesia, Burning, pins & needles 

-‐

Expansion of syrinx 

Decussating fibres of the spinothalamic tracts affected firstparasthesia 

of associate dermatome 

Dorsal horn is plastic




• Forelimb weakness, hindlimb ataxia 

-‐Expansion of syrinx into ventral 

columns, white maaer





• Scoliosis; may be seen as head /lt

Scoliosis 

• Relationship between 

cervical scoliosis and syrinx 

width 

• Probably not due to loss of 

muscle innervation 

• Appears to be associated 

with loss of afferent 

information from the cervical 

neuromuscular spindles





• Scoliosis 

• Signs due to SM or CM

Is all pain associated with 

syringomyelia 

Overcrowding of the foramen magnum may cause pressure on brainstem nuclei 

causing signs of pain. 9/48 clinical dogs in one study CM only 

November 17, 2012 | Veterinary Record





• Scoliosis 

• Asymptoma)c 

-‐ 60% CKCS breeding stock 

have a syrinx and no signs!

Clinical signs not due to SM 

• CKCS have lots of problems…. 

-‐Seizures. unrelated to CM/ SM, hydrocephalus* 

-‐Idiopathic facial palsy is common in the CKCS 

-‐so is hearing impairment 

*The Veterinary Journal 195 (2013) 235–237

What is Chiari-‐like Malforma/on 

• “Occipital hypoplasia” 

• Analogous to Chiari I malforma/on 

of humans 

Miller’s anatomy of the dog


• Occipital hypoplasia: Caudal Fossa too small for cerebellum 

• -‐Reduced volume of the caudal fossa 

• A reduced volume of the occipital bone was not found in Cavalier King Charles 

spaniels in general in comparison to French bulldogs 

• or Cavalier King Charles spaniels with syringomyelia compared to Cavalier King 

Charles spaniels without syringomyelia 

Vet Radiol Ultrasound, Vol. 53, No. 5, 2012, pp 540–544



• -‐Reduced volume of the caudal fossa 

• Increased hindbrain volume in CKCS causes the tentorium cerebelli to 

compensate by bulging in a rostral direc/on 

• “pars caudalis” rela/vely insensi/ve to increase cerebellar size. 

T. A. Shaw Veterinary Record (2013)



• CKCS has a rela/vely larger cerebellum 

than small breed dogs and Labradors 

• Also larger in young CKCS with CM and SM 

than in older CKCS with CM alone 

Thomas A. Shaw 

PLoS One. 2012; 7(4): e33660.

Indenta/on of cerebellum (CKCS) 

Upward “kink” at cervicomedullary junc/on

Chiari-‐like Malforma/on 

• Hernia/on of the cerebellar vermis 

• “Gap” Between cerebellum and brain stem

Shortened 

Basicranium

Pathogenesis of CM> SM 

-‐Theories only

Systolic CSF pulses 

Miller’s Anatomy

Waterhammer 

Effect 

• CSF forced down the central canal from the 

fourth ventricle due to increased intrathoracic 

or abdominal pressure 

• Relies on a communica/on between the 

fourth ventricle and the central canal 

• Would expect to also result in hydrocephalus

Piston Theory 

• Displaced cerebellar tonsils act like a piston 

and with each systole are forced caudally 

• Pressure wave within the entrapped 

subarachnoid space and syrinx 

• Also relies on CSF being forced into the spinal 

cord from the subarachnoid space. 

• Would seem more likely to be crushed than 

expand with a syrinx

Suck effect 

• Based on inability of pressure to equilibrate 

due to foramen magnum obstruc/on 

• Similarly reliant on fourth ventricle 

communica/on 

• Implies low syrinx pressure

Slosh Effect 

• Pressure differences can cause a surge of fluid 

within the syrinx, resul/ng in further fissuring 

and damage to the spinal cord 

• This is thought to be important for the 

con/nued development of a syrinx

BUT: 

• Fluid thought to be of extracellular origin not 

CSF. 

• Syringomyeilia o\en start non-communica/ng 

 

• Chiari dogs o\en have hyperintensity on T2 

dorsal to central canal before development of 

syrinx

Intramedullary 

Pulse Pressure Theory 

• Holds true regardless of ae/ology 

• Transmission and reflec/on of the systolic CSF 

pulse pressure into spinal cord /ssue 

• Low pressure in sub-‐arachnoid space due to 

pulse velocity and turbulence. 

• This repeated mechanical distension of the 

cord results in dilata/on of the central canal 

and accumula/on of extracellular fluid which 

eventually coalesces into cavi/es

• Venturi effect 

Bernoulli's principle

CEREBROSPINAL FLUID FLOW 

• CSF flow velocity assessed using phase-contrast 

cine MRI at the foramen magnum 

• Velocity in the dorsal aspect of the 

subarachnoid space at the foramen magnum 

significantly lower in CKCS 

• Turbulent flow and jets were associated with 

syringomyelia presence and severity 

CERDA-‐GONZALEZ. Veterinary Radiology & Ultrasound, Vol. 50, No. 5, 2009

Other causes of CSF flow 

obstruc/on causing SM

What causes SM when 

CM not present

SM 

without 

CM 

CM 

Without 

SM

Is 

‘Gap’ size 

more 

useful

Volume reduc/on of the 

jugular foramina 

• CKCSs without SM presented 

significantly larger JF volumes when 

compared with CKCSs with SM 

• Link between brachycephaly and abnormal 

CSF flow can be found in the skull base 

• May explain the ae/ology of CSF pressure 

waves in the subarachnoid space, 

independent of cerebellar hernia/on 

Schmidt et al. BMC Veterinary Research 2012, 8:158

Diagnosis 

• Ultrasonography has a low sensi/vity for 

diagnosis of Chiari-‐like malforma/on/ 

syringomyelia. 

• Rads may reveal a short caudal fossa– 

subjec/ve. Myelography risky 

• CT most effec/ve way of defining boney 

structures of CM 

• Only definite way to diagnose syringomyelia is 

by MRI. Posi/oning 

Journal of small Animal Prac/ce (2008) 49, 438–443 Vet Radiol Ultrasound, Vol. 53, No. 5, 2012, Vol. 49, No. 5, 2008

Differen)al Diagnosis-‐Pain 

• IVDD 

• GME 

• AA luxa/on 

• Neoplasia 

• Trauma 

• Discospondyli/s 

• Bacterial meningi/s

Differen)al Diagnosis-‐ Scratching 

• Ear disease-‐ PSOM 

• Skin disease 

• Head-‐Foot irrita/on syndrome

Factors associated with the presence 

of neurologic signs 

• Syringomyelia, degree propor/onate to size 

• Ra/o of caudal fossa/total cranial cavity 

volume was significantly smaller in clinically 

affected Cavalier King Charles Spaniels 

Veterinary Radiology & Ultrasound, Vol. 50, No. 1, 2009

Prevalence: 

• Most CKCS affected by CM 

-‐87.5% asymptoma/c had occipital hypoplasia based on 

subjec/ve criteria of crowding 

• Many ‘normal’ dogs have syringomyelia 

-‐27% compared with 88% dogs with neurologic signs 

-‐ 60% in Sydney’s responsible breeding popula/on 

Veterinary Radiology & Ultrasound, Vol. 50, No. 1, 2009,

Medical treatment 

• Typically does not resolve, the clinical signs. 

• NSAIDs for mild pain 

• Pred effec/ve. Dose> adverse side effects 

• Gabapen/n / Pregabalin 

• Oral opioids 

• Frusemide 

• Omeprazole, tricylic an/depressants

Long-‐term outcome 

• Clinical signs sugges)ve of Neuropathic Pain 

progress in three-‐quarters 

• 75 per cent s/ll alive 39 (±14.3) months later, 

with an acceptable QOL 

November 17, 2012 | Veterinary Record

Surgical Treatment 

• People with Chiari I receive foramen magnum 

decompression 

• Success controlling symptoms in humans is 

high 

• High rate of re-‐opera/on, mostly due to scar 

/ssue causing recurrent stenosis

Foramen magnum 


• Based on premise of CM being homologous to 

Chiari I of humans and COMS being sole cause 

• Minimal intra-‐opera/ve complica/ons 

• 1/16 dog died, and 1 euthana/zed. 

• Signs resolved in 7/16 dogs 

• Improved in 6/16 dogs, and 

• Remained unchanged in 1 dog. 

Dewey. JAVMA, Vol 227, No. 8, October 15, 2005

Follow up MRIs-‐ Scar /ssue 

• 1 dog unchanged post Foramen magnum 


• 3 dogs deteriorated a\er ini/al improvement 

– 2/3 improved following second surgery, 1 died 

• Marsupializa/on 5 dogs-‐ no further Sx

Foramen magnum 


• All dogs made a quick recovery a\er surgery 

and were exercising normally within 4 weeks 

• No dogs had complete resolu/on of signs 

• 12/15 improved 

• 47% subsequently deteriorated 0.2 – 2.3 years 

• Gross inspec/on revealed 

layers of scar /ssue in 2 

C. Rusbridge– Veterinary Surgery

• Dura/on of clinical signs prior to surgery was 

strongly correlated with outcome. 

• Shape/ size of the syrinx unchanged

Treatment 

• Results—No intraopera/ve 

complica/ons 

• Worsening of a pre-‐exis/ng head /lt and ataxia in 

1/21 dogs 

• Seventeen (81%) had clinical improvement 

• 25% required re-‐opera/on 

• 2 dogs were euthana/zed 

• Follow-‐up 11.2 months (3.5–21 

• Vs 16m 

DEWEY et al Veterinary Surgery 36:406–415, 2007

Treatment-‐ 

Syringosubarachnoid 

shunt 

• No intra-‐ or peri-‐opera/ve 

complica/ons 

• Progressive neurological 

improvement in 9/11 dogs 2 

weeks and 6 months 

postopera/vely 

• 7 contacted long term and no 

deteriora/on 

• Resolu/on of Syrinx 1/3 

Journal of Small Animal 

PracBce (2012) 53, 205–212

Where to for CKCS 

• Complex mode of inheritance 

• Already /ny gene pool with mul/ple other 

disease concerns 

• DNA collec/on 

program is underway

Acknowledgments 

• Clare Rusbridge 

• BVMS PhD DipECVN

Acknowledgments 

Georgina Child 

BVSc Diplomate ACVIM (Neurology)

Syringomyelia

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