Imaging Studies
MRI is the most useful and most widely used imaging study for diagnosing Chiari malformation. In addition to depicting the anatomy of the craniocervical junction, it provides useful information about associated abnormalities, such as syringomyelia and hydrocephalus. [8]
Patients who cannot undergo MRI can be evaluated with CT-myelography/cisternography. However, the increasing availability of high-resolution high-speed (eg, 64-slice) CT scanners allows for making the diagnosis with a noncontrast CT with sagittal reconstructions, obviating the need for myelography.
CSF flow analysis through foramen magnum with phase-contrast cine MRI helps distinguish symptomatic Chiari I from asymptomatic cerebellar ectopia [6] and helps predict response to surgical decompression. [7]
CSF flow study with phase-contrast cine MRI. Brain pulsations results in caudad and cephalad flow of CSF across foramen magnum during systole and diastole. The reversal in the direction of flow is picked up by alternating light and dark appearance of CSF in front and behind the medulla and upper spinal cord on phase-contrast cine MRI. In this case of Chiari I malformation, note the complete absence of CSF flow behind (arrowheads) and focal constriction of CSF flow (arrows) in front of cervicomedullary junction.
Laboratory Studies
Lab studies are not applicable for diagnosing Chiari malformations.
Preparation for surgery for Chiari I decompression is the same as for any elective surgery and depends on the patient's general health. The author routinely obtains CBC, basal metabolic panel, PT, aPTT, chest radiograph, and ECG. Blood is typed and screened.
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Sagittal and coronal MRI images of Chiari type I malformation. Note descent of cerebellar tonsils (T) below the level of foramen magnum (white line) down to the level of C1 posterior arch (asterisk).
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Axial MRI image at the level of foramen magnum in Chiari type I malformation. Note crowding of foramen magnum by the ectopic cerebellar tonsils (T) and the medulla (M). Also note the absence of cerebrospinal fluid.
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Occipitalization of atlas in a patient with Chiari I.
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T2 hyperintense region on MRI (arrow) depicting edema in central cord region of a patient with Chiari I malformation. Left untreated, this patient is likely to develop cavitation of the edematous central cord, resulting in syringomyelia.
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CSF hypotension syndrome: Postcontrast MRI before (A) and after (B) treatment with lumbar epidural blood patch. Notice the thick meningeal enhancement (arrows), the relative paucity of CSF in front of the brainstem and behind the cerebellar tonsils, and the engorgement of the pituitary gland before treatment (A). Notice reversal of these abnormalities and ascent of the cerebellar tonsils after treatment (B). In this case, an acquired Chiari malformation was not present, but in some cases it is.
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CSF flow study with phase-contrast cine MRI. Brain pulsations results in caudad and cephalad flow of CSF across foramen magnum during systole and diastole. The reversal in the direction of flow is picked up by alternating light and dark appearance of CSF in front and behind the medulla and upper spinal cord on phase-contrast cine MRI. In this case of Chiari I malformation, note the complete absence of CSF flow behind (arrowheads) and focal constriction of CSF flow (arrows) in front of cervicomedullary junction.
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Resolution of syringomyelia (asterisk) after decompression of Chiari I malformation (white arrow).
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Intraoperative photograph of Chiari type 1 malformation showing descent of cerebellar tonsils well below the level of foramen magnum.
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Intraoperative photograph of duraplasty with pericranial graft. The duraplasty provides additional room for cerebellar tonsils at the craniocervical junction, while achieving closure of dura and prevention of cerebrospinal fluid leak.
Tables
Characteristic |
Chiari I |
Chiari II |
Usual age of diagnosis |
Adults and older children |
Infants and young children |
Clinical findings |
|
|
Primary anatomical abnormalities |
|
|
Myelomeningocele |
No |
Always |
Hydrocephalus |
Less than 10% of cases |
Very common |
Syringomyelia |
30-70% |
Common |
Associated abnormalities |
|
|
Shared associated abnormalities |
|
|
