Table 1.

Definitions of features of Chiari II malformation

Feature	Definition	Reference
Sagittal plane
Downward herniation cerebellum	Either vermis, tonsil, or part of the cerebellum, below the foramen magnum	Variend and Emery [9]
Downward herniation vermis	Vermis below the foramen magnum	Variend and Emery [9]
Downward herniation tonsil	At least one tonsil below the foramen magnum	Variend and Emery [9]
Upward herniation cerebellum	Bulging of the cerebellum through the tentorial incisura	Peach [7] and Naidich et al. [12]
Downward displacement medulla	Stretching and downward displacement of the medulla below the foramen magnum	Emery and MacKenzie [8]
Downward displacement pons	Stretching and downward displacement of the pons towards spinal canal	Naidich et al. [14]
Downward displacement fourth ventricle	Stretching and downward displacement of the fourth ventricle	Emery and MacKenzie [8]
Medullary kinking	Kink of the medulla dorsal to the upper cervical spinal cord	Emery and MacKenzie [8]
Flattened pons	Thin stretched pons	El Gammal et al. [16]
Abnormal width fourth ventricle	Collapsed or dilated fourth ventricle	Wolpert et al. [15]
Hypoplastic tentorium	Underdeveloped tentorium with abnormally low insertion at the occipital bone	Peach [7] and Naidich et al. [11]
Abnormal course straight sinus	Abnormally short, steep course, or low insertion of the straight sinus	El Gammal et al. [16] and Just et al. [17]
Beaked tectum	Deformity of the quadrigeminal plate appearing like a pointed or bulbous mass	Peach [7] and Wolpert et al. [15]
Enlarged massa intermedia	Thick interthalamic adhesion	Peach [7] and Naidich et al. [13]
Stenogyria	Innumerable, closely spaced small gyri at the occipital cortex	Peach [7] and Wolpert et al. [15]
Axial plane
Cerebellum in cervical spinal canal	Cerebellum below the top of the dens or the base of the occipital condyles	Variend and Emery [9]
Vermis in cervical spinal canal	Vermis below the top of the dens or the base of the occipital condyles	Variend and Emery [9]
Tonsil in cervical spinal canal	At least one tonsil below the top of the dens or the base of the occipital condyles	Variend and Emery [9]
Cerebellum wrapped around brainstem	Cerebellar hemispheres wrapped around brainstem into cerebellopontine angle cisterns	Peach [7] and Naidich et al. [12]
Abnormal fissural pattern of cerebellum	Abnormal fissural and lobular pattern of the superior surface of the cerebellum	Variend et al. [10]
Small fourth ventricle	Collapsed fourth ventricle	Wolpert et al. [15]
Enlarged fourth ventricle	Dilated fourth ventricle	Wolpert et al. [15]
Beaked tectum	Quadrigeminal plate is stretched appearing beaked	Peach [7] and Naidich et al. [12]
Enlarged massa intermedia	Thick interthalamic adhesion	Peach [7] and Naidich et al. [13]
Gyral interdigitation	Gyri crossing the interhemispheric fissure and folding in contralateral sulci	Peach [7] and Just et al. [17]
Stenogyria	Innumerable, closely spaced small gyri at the occipital cortex	Peach [7] and Wolpert et al. [15]
Coronal plane
Downward herniation cerebellum	Cerebellum below the base of the occipital condyles	Variend and Emery [9]
Downward herniation vermis	Vermis below the base of the occipital condyles	Variend and Emery [9]
Downward herniation tonsil	At least one tonsil below the base of the occipital condyles	Variend and Emery [9]
Upward herniation cerebellum	Upward bulging of the cerebellum (towering) through a wide tentorial incisura	Peach [7] and Wolpert et al. [15]
Indentation	Indentation of the cerebellum by the edge of the tentorium	Peach [7] and Naidich et al. [12]
Hypoplastic tentorium	Short tentorial leaves with a wide tentorial incisura	Peach [7] and Naidich et al. [11]
Gyral interdigitation	Gyri crossing interhemispheric fissure and folding in contralateral sulci	Peach [7] and Just et al. [17]