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Media Gallery

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).
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.
Occipitalization of atlas in a patient with Chiari I.
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.
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.
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.
Resolution of syringomyelia (asterisk) after decompression of Chiari I malformation (white arrow).
Intraoperative photograph of Chiari type 1 malformation showing descent of cerebellar tonsils well below the level of foramen magnum.
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.

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Table 1. Comparison of Chiari I and II Malformations

Table 1. Comparison of Chiari I and II Malformations

Characteristic	Chiari I	Chiari II
Usual age of diagnosis	Adults and older children	Infants and young children
Clinical findings	Headache and neck pain (worsened by cough or Valsalva maneuver) Myelopathy Cerebellar symptoms Lower brainstem symptoms (eg, dysarthria, dysphagia, downbeat nystagmus) Central cord symptoms (eg, hand weakness, dissociated sensory loss, cape anesthesia)	In infants, signs of brainstem dysfunction predominate: swallowing/feeding difficulties, stridor, apnea, weak cry, nystagmus Weakness of extremities
Primary anatomical abnormalities	Herniation of cerebellar tonsils through foramen magnum, producing compression of cervicomedullary junction	Herniation of lower brainstem through foramen magnum Cephalad course of cranial nerves Kinking of cervicomedullary junction "Beaking" of tectum Upward herniation of vermis through incisura Nearly vertical tentorium
Myelomeningocele	No	Always
Hydrocephalus	Less than 10% of cases	Very common
Syringomyelia	30-70%	Common
Associated abnormalities	Craniocervical hypermobility syndromes Klippel-Feil anomaly Hereditary connective tissue disorders and neurofibromatosis type II	Callosum corpus pellucidum septum of agenesis Hypoplasia or Enlargement of massa intermedia Heterotopias and gyral abnormalities
Shared associated abnormalities	Basilar invagination Occipitalization of atlas Bifida of C1 posterior arch Foramen magnum variant anatomy	Basilar invagination Occipitalization of atlas Bifida of C1 posterior arch Foramen magnum variant anatomy

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