One Dozen Expert Statements on Chiari Zero Malformation

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One Dozen Expert Statements on Chiari Zero Malformation

1. Cerebellar Tonsillar ectopia is considered of clinical significance

only when both tonsils are herniated at least 3mm below the foramen magnum.

This criterion is too restrictive. We conclude that even minimal tonsillar

ectopia can be symptomatic and that surgical decompression of the foramen

magnum can be beneficial. The clinical significance of tonsillar ectopia

should be determined by the crowding of the contents of the foramen magnum

rather than simply by a measure of tonsillar descent.

2. Tonsillar descent of the cerebellum in Chiari I malformations is

often considered a congenital defect. A patient is presented in whom

magnetic resonance (MR) imaging revealed normally positioned cerebellar

tonsils; however, 1 year later MR imaging was repeated for evaluation of

gait abnormalities and showed descent of the cerebellar tonsils. This case

illustrates worsening symptoms with progressive descent of the cerebellar

tonsils and suggests that Chiari I malformations can evolve postnatally.

Note: One would then reason that ACM is not necessarily congenital i.e. is

not always pre-existing.

3. But if you look here at the T-2 weighted images where spinal fluid

is white behind the cerebellum you can see this is a compressed posterior

fossa with an absence of CSF posteriorally and lateral to the cerebellum.

This is a Chiari Malformation with the tonsils at the level of the foramen

magnum, and not grossly below it. So we are redefining the Chiari

Malformation as not simply how far the tonsils come down, but it is a

diagnosis, which includes 7 specific signs. They include: the volume of the

posterior fossa being small, CSF volume being reduced, compression owing to

smallness of the bones in the back and most of them have varying degrees of

tonsillar herniation. The failure to have greater than 3 mm to 5 mm

herniation does not exclude the diagnosis of Chiari I in our new

definition. … Normal tonsils should lie 2mm ABOVE the foramen magnum.

4. Magnetic resonance images obtained in the five cases of Chiari zero

malformations reported by Iskandar, et al. The tonsils are at the level of

the formen magnum. All five patients had syringomyelia that resolved after

posterior fossa decompression. Used with permission from Iskandar, et

al:The resolution of syringohydromyelia without hindbrain herniation after

posterior fossa decompression.

5. " isolated tonsillar herniation is of limited prognostic utility,

and should be considered in the context of all available clinical and

imaging data.... " .

6. There are patients in whom the tonsillar herniation extends less

than 5 mm from the foramen magnum, whose clinical behavior is similar to

the remainder of the Chiari population.

7. Tubbs, et al., added a sixth case and analyzed various radiological

indices, finding that the contents of the posterior fossa were indeed

compromised in these patients, even in the absence of tonsillar ectopia,

and that the obices were located more than two standard deviations below

normal. " Chiari zero malformation " was the name they chose to characterize

the disorder.

8. These results further support the hypothesis that syrinx formation

may be induced by junctional CSF flow obstruction, even in the absence of

tonsillar descent.

9. Perhaps a mor apt description would be borderline Chiari

Malformation characterized by low-lying tonsils, caudal displacement of the

brainstem, and underdevelopment of the posterior fossa” The absiense of

tonsillar octopi on midsagittal MRI scans may understate the incidence of

minimal tonsilar herniation.

10. In patients with idiopathic syringomyelia, it advisable to obtain

an exhaustive neuroradiological workup that is focused on the detection of

occult CSF blocks. Cine MRI and computed tomographic myelography are often

helpful in this regard.

11. Two patients with syringomyelia and tonsillar position of less than

5 mm below the position received surgical treatment …. Had significantly

abnormal CSF flow profiles. In addition, a progression of their tonsillar

descent was observed in two patients while being followed prior to surgical

intervention.

12. Whereas tonsillar position provides a general screening parameter,

the CSF profile dynamics provide equally useful parameter in diagnosis of

Chiari I Malformation.

Sources:

1. Dan S. Heffez, M.D., et al:http://www.nfra.net/Chiari6.htm> Chiari

Malformations Abstract VI, Trivial Degrees of Tonsillar

Ectopiahttp://www.nfra.net/Chiari6.htm> May be Symptomatic

2. Huang PP, Constantini S, New York University Medical Center,

" http://www.pressenter.com/~wacma/acquired.htm>Acquired "

Chiarihttp://www.pressenter.com/~wacma/acquired.htm> I malformation. Case

report.

3. Milhorat T, Neurosurgery, University of

NY,http://www.asap4sm.com/docscorner/milhorat01.html> Four Year Study of

Chiarihttp://www.asap4sm.com/docscorner/milhorat01.html> I Malformation

Highlights of ASAP conference.

4. Iskandar BJ, et al:

http://www.neurosurgery.org/focus/mar00/8-3-4.pdf>The resolution of

syringohydromyelia without hindbrain herniation after posterior

fossahttp://www.neurosurgery.org/focus/mar00/8-3-4.pdf> decompression.

5. Meadows J., et al:

http://www.neurosurgery.org/focus/july01/11-1-1.pdf>Asymptomatic

Chiarihttp://www.neurosurgery.org/focus/july01/11-1-1.pdf> Type I

malformations identified on magnetic resonance imaging.

6. Ghassan K. Bejjani, M.D., University of Pittsburgh,

http://www.neurosurgery.org/focus/july01/11-1-1.pdf>Definition of the

Adult Chiarihttp://www.neurosurgery.org/focus/july01/11-1-1.pdf>

Malformation: A Brief Historical Overview

7. Tubbs RS, Elton S, Grabb P, et al:

http://www.neurosurgery.org/focus/july01/11-1-1.pdf>Analysis of the

posterior fossa in children with the

Chiarihttp://www.neurosurgery.org/focus/july01/11-1-1.pdf> 0 malformation.

8. Alfieri A., et al:

http://www.damm-virtuell.de/dgnc2002/vortrag/Abstract_vortrag1504_129.pdf>Syrin\

gomyelia

not associated to hind-brain herniation: the surgical treatment of the so

called

“Chiarihttp://www.damm-virtuell.de/dgnc2002/vortrag/Abstract_vortrag1504_129.pd\

f>

0 Malformation”.

9. Milhorat, T., Nuerosurgery,

http://www3.sympatico.ca/ejfs/acm0_milhorat.pdf>Volhttp://www3.sympatico.ca/ej\

fs/acm0_milhorat.pdf>

48, No. 5, May 2001

10. Milhorat, T.,

Nuerosurgery, http://www3.sympatico.ca/ejfs/acm0_milhorat.pdf>Vol 48, No.

5, May 2001

11. G. Ellenbogen, et

al:http://www.neurosurgery.org/focus/mar00/8-3-5.pdf> Toward a rational

treatment of Chiari I malformation and

syringomyeliahttp://www.neurosurgery.org/focus/mar00/8-3-5.pdf>.

12. G. Ellenbogen, et al:

http://www.neurosurgery.org/focus/mar00/8-3-5.pdf>Toward a rational

treatment of Chiari I malformation and

syringomyelia.http://www.neurosurgery.org/focus/mar00/8-3-5.pdf>