incidence of acm and asymtomatic numbers ect

October 2, 2000

I ran across this this am , ......good large study on the incidence of acm in

the general population .....and the number of folks with asymptomaic acm ect

......those figures tossed out last week ,seemed grapevine distorted i think

.....but may well have started with this article /abstract .

taken from a link at the asap site ......

1: J Neurosurg 2000 Jun;92(6):920-6 Related Articles, Books, LinkOut

Asymptomatic Chiari Type I malformations identified on magnetic resonance

imaging.

Meadows J, Kraut M, Guarnieri M, Haroun RI, Carson BS

Department of Neurological Surgery, s Hopkins Hospital, Baltimore,

land 21287-8811, USA.

OBJECT: Chiari Type I malformation (CMI) is a congenital disorder recognized

by caudal displacement of the cerebellar tonsils through the foramen magnum

and into the cervical canal. Frequently, associated findings include

abnormalities of nearby bony and neural elements as well as syringomyelia.

Cerebellar tonsillar ectopia is generally considered pathological when

greater than 5 mm below the foramen magnum. However, asymptomatic tonsillar

ectopia is an increasingly recognized phenomenon, the significance of which

is poorly understood. METHODS: The authors retrospectively reviewed the

records of all brain magnetic resonance (MR) images obtained at our hospital

over a 43-month period in an attempt to ascertain the relative prevalence and

MR imaging characteristics of asymptomatic CMIs. Of 22,591 patients who

underwent MR imaging of the head and cervical spine, 175 were found to have

CMIs with tonsillar herniation extending more than 5 mm below the foramen

magnum. Of these, 25 (14%) were found to be clinically asymptomatic. The

average extent of ectopia in this population was 11.4 +/- 4.86 mm, and was

significantly associated with a smaller cisterna magna. Syringomyelia and

osseous anomalies were found in only one asymptomatic patient. CONCLUSIONS:

The authors suggest that the isolated finding of tonsillar herniation is of

limited prognostic utility and must be considered in the context of all

available clinical and radiographic data. Strategies for treating patients

with asymptomatic CMIs are discussed.

PMID: 10839250, UI: 20296060

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