Chiari I Malformation Redefined:
Clinical and Radiographic Findings 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.
Departments of Neurosurgery (THM, MWC, EMT), Neurology (RWK), and Radiology
(MM), State University of New York Health Science Center at Brooklyn,
Brooklyn, New York; The Long Island College Hospital (THM, MWC, EMT, RWK),
Brooklyn, New York; and the Department of Medicine (CW, MCS), Section
of Medical 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.
(Neurosurgery 44:1005-1017, 1999)
Presented at the National Fibromyalgia Research Association's Subgroups
in Fibromyalgia Symposium, September 26-27, 1999, in Portland,