Journal of Neurosurgery Vol 44, Pages 1005-1017
Chiari 1 Malformation Redefined: Clinical and Radiographic
for 364 Symptomatic Patients
Thomas H. Milhorat, M.D., Mike W. Chou, M.D.,
Elizabeth M. Trinidad, M.D., Roger W. Kula, M.D.,
Menachem Mandell, M.D.,
Chantelle Wolpert, M.B.A., P.A.-C.,
Marcy C. Speer, Ph.D.
of Neurosurgery (THM, MWC, EMT), Neurology (RWK), and Radiology
State University of New York Health Science Center at Brooklyn,
York; The Long Island College Hospital (THM, MWC, EMT, RWK),
New York; and the Department of Medicine (CW, MCS), Section of
Genetics, Duke University Medical Center, Durham, North Carolina
OBJECTIVE: Chiari malformations are regarded as a
pathological continuum of hindbrain maldevelopments characterized by
downward herniation of the cerebellar tonsils. The Chiari I malformation
(CMI) is defined as tonsillar herniation of at least 3 to 5 mm below the
foramen magnum. Increased detection of CMI has emphasized the need for
more information regarding the clinical features of the disorder.
METHODS: We examined a prospective cohort of 364 symptomatic
patients. All patients underwent magnetic resonance imaging of the head
and spine, and some were evaluated using CINE-magnetic resonance imaging
and other neurodiagnostic tests. For 50 patients and 50 age- and gender-
matched control subjects, the volume of the posterior cranial fossa was
calculated by the Cavalieri method. The families of 21 patients
participated in a study of familial aggregation.
RESULTS: There were 275 female and 89 male
patients. The age of onset was 24.9+/-15.8 years (mean +/- standard
deviation), and 89 patients (24%) cited trauma as the precipitating
event. Common associated problems included syringomyelia (65%),
scoliosis (42%), and basilar invagination (12%). Forty-three patients
(12%) reported positive family histories of CMI or syringomyelia.
Pedigrees for 21 families showed patterns consistent with autosomal
dominant or recessive inheritance. The clinical syndrome of CMI was
found to consist of the following: 1) headaches, 2) pseudotumor-like
episodes, 3) a Meniere's disease-like syndrome, 4) lower cranial nerve
signs, and 5) spinal cord disturbances in the absence of syringomyelia.
The most consistent magnetic resonance imaging findings were
obliteration of the retrocerebellar cerebrospinal fluid spaces (364
patients), tonsillar herniation of at least 5 mm (332 patients), and
varying degrees of cranial base dysplasia. Volumetric calculations for
the posterior cranial fossa revealed a significant reduction of total
volume (mean, 13.4 ml) and a 40% reduction of cerebrospinal fluid volume
(mean, 10.8 ml), with normal brain volume.
CONCLUSION: These data support
accumulating evidence that CMI is a disorder of the para-axial mesoderm
that is characterized by underdevelopment of the posterior cranial fossa
and overcrowding of the normally developed hindbrain. Tonsillar
herniation of less than 5 mm does not exclude the diagnosis. Clinical
manifestations of CMI seem to be related to cerebrospinal fluid
disturbances (which are responsible for headaches, pseudotumor-like
episodes, endolymphatic hydrops, syringomyelia, and hydrocephalus) and
direct compression of nervous tissue. The demonstration of familial
aggregation suggests a genetic component of transmission.