Growing Evidence Demonstrating Significance of Minimal or no Herniation of Cerebellar Tonsils
The authors report four cases of syringomyelia thought to be idiopathic
syringomyelia but treated by craniocervical
decompression with favorable results. Syringomyelia was present without hindbrain herniation. In such cases, the
subarachnoid space anterior to the brainstem at the level of the foramen magnum is usually open but the cisterna magna
is impacted by the tonsils, a condition the authors term "tight cisterna magna."
... Syringomyelia associated with tight cisterna magna should not be classified as idiopathic syringomyelia;
rather, it belongs to the category of organic syringomyelia such as Chiari malformation. A possible pathogenesis of
cavitation is obstruction of the CSF outflow from the foramen of Magendie, and the cavity may be a communicating
dilation of the central canal.
Cases are presented that highlight the possible connection between
familial syringomyelia and the Chiari 0 malformation.
Magnetic resonance imaging further revealed that one brother had Chiari I malformation and the other had Chiari 0
malformation. Both underwent posterior fossa decompression with radiologic improvement of their syringes. These case
reports lend credence to earlier reports of improvement in syringomyelia following posterior fossa decompression in
the absence of Chiari I malformation, the so-called Chiari 0 malformation.
Milhorat and Bolognese report an excellent technique application. Dr.
Milhorat is a member
of the scientific community who possibly performs more CMI operations than any other surgeon
in the United States. He shows that he meticulously studies each patient and each approach
so that he may improve on what has been done previously. ... This is an enormous advantage for
those surgeons who base their treatment on the correction of the anatomic and thus the
physiological conditions that exist in the posterior fossa. ... First, however, the authors must
show how this technique and the subsequent tailored surgical approach correlate with patient
outcome in terms of symptoms and radiological criteria such as magnetic resonance imaging.
In the next several years, I have little doubt that Milhorat and Bolognese will do precisely that.
...Richard G. Ellenbogen, Seattle, Washington
"In recent years, the term CMI has been used synonymously with
tonsillar ectopia or chronic tonsillar herniation in a wide variety
of congenital and acquired disorders. The radiological definition
of CMI has been reported as tonsillar herniation of at least 3 mm
or at least 5 mm below the foramen magnum. However,
this definition is limited to a single criterion and makes no
reference to clinical symptoms or the presence or absence of
associated findings such as syringomyelia.
The radiological definition of CMI may be too restrictive. In
this study, there were 32 of 364 patients (9%) who exhibited
tonsillar herniation of less than 5 mm and symptoms that
were typical of CMI. Seventeen of those 32 patients (53%) had
syringomyelia. All patients showed MRI evidence of hindbrain
overcrowding, and CINE-MRI demonstrated
abnormalities of CSF velocity/flow that were similar
to those reported for patients with tonsillar herniation of at
least 5 mm. These observations indicate that the
extent of tonsillar herniation cannot be used as the sole criterion
for the diagnosis of CMI. We could not confirm reports
that the severity of symptoms is directly related
to the extent of tonsillar herniation. Because tonsillar herniation
of at least 5 mm can be encountered as an incidental
finding among asymptomatic patients, it is likely that the
position of the cerebellar tonsils, although providing a general
index of hindbrain overcrowding, is only one factor influencing
the clinical features of CMI."
"Minimal evidence of hindbrain
overcrowding consists of obliteration of the retrocerebellar CSF
spaces in association with a meniscus sign at the lower pole of
the cerebellar tonsils. CINE-MRI can be helpful in demonstrating
a disturbance of CSF velocity/flow at the foramen magnum in
patients with tonsillar herniation of less than 5 mm."
"Minimal evidence of hindbrain overcrowding consisted of obliteration
the retrocerebellar CSF spaces in association with a meniscus
sign at the lower pole of the cerebellar tonsils. For 47 of 364
patients who underwent phase-contrast CINE-MRI, including
21 patients with tonsillar herniation of less than 5 mm,
there was evidence of decreased CSF velocity/flow in the
cisterna magna and subarachnoid space posterior to the cerebellum
(47 patients) and the premedullary and prepontine
spaces anterior to the brain stem (15 patients)."
"The most constant abnormality was compression
of the CSF spaces posterior and lateral to the cerebellum
(364 patients, 100%). Tonsillar herniation of at least 5 mm
below the foramen magnum was present in 332 patients (91%)."
"Milhorat et al. provide an extensive amount of information
on the so-called CMI. On the basis of their very large case
series, they have been able to define the clinical syndrome in
a more comprehensive way than was previously possible.
They also have related this condition to the volume of the PCF
and have provided some evidence that CMI is a disorder of
the para-axial mesoderm. The data provided will facilitate
evaluation of patients in the future. CMI, more than ever,
becomes only a useful shorthand term for a disorder that is
even more complex than was previously realized."
...Ulrich Batzdorf, Los Angeles, California
"Only patients with caudal displacement of the cerebellar tonsils of less than 3.0 mm were included in this series."
"In our experience, limiting the diagnosis of the Chiari
type 1 malformation to cerebellar tonsil ectopia of 3-5 mm or greater below the rim of
the foramen magnum may be too restrictive. Patients with lesser
degrees of tonsillar ectopia who complain of symptoms consistent with compression of
the structures coursing through the foramen magnum could potentially be denied the
benefits of decompressive surgery."
"Despite the minimal degree of tonsillar ectopia, our patients reported
improvement in symptoms
in response to surgical enlargement of the foramen magnum. An improvement in
objective neurological signs was also noted."
"We suggest that the Chiari type 1
malformation should be viewed as a relative disproportion between the cross sectional
area of the foramen magnum and the structures coursing through it rather than strictly as a
measure of tonsillar ectopia. If the structures within the foramen magnum are crowded,
then the patient may be symptomatic in the face of a minor degree of tonsillar ectopia.
Surgical decompression may be appropriate in selected cases."
"There would be
cases, where there is no significant tonsillar ectopia and no
visual loss but the myriad of other symptoms similar to those seen in ACM and IIH.
These are the most challenging cases to diagnose. It is this group that is eliciting the most
controversy: patients with ACM like symptoms but no or minimal tonsillar descent, which
improve with suboccipital decompression. With the lack of objective findings like tonsillar
descent or papilledema, some of these patients are considered functional or given various
generic diagnoses like chronic fatigue syndrome and fibromyaglia."
"if you look here at
the T-2 weighted images where spinal fluid is white behind the
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."
"Caudal descent between 0 and 5mm needs to be put in the clinical content of the individual patient."
"Surgical intervention for Chiari I malformation is relatively safe."
"Diagnosis can be difficult
not all patients will have the classical sign of deeply herniated
"Two patients with syringomyelia and tonsillar position less than 5 mm
the opisthion received surgical treatment. In the remaining surgical
candidates the tonsils had descended 3 mm or more below the opisthion."
"Sixty-five patients with Chiari I malformation were
studied. In patients with herniation of the cerebellar tonsils
located more than 3 mm below the opisthion of the
foramen magnum, obstructed CSF flow was demonstrated.
This was manifest by decreased flow velocities and a
shorter period of caudal CSF flow in Magendie's foramen
and foramen magnum. In two patients tonsillar ectopia
was of 3 mm or less, but both had holocord syringes. Both
patients with borderline tonsillar ectopia 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."