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In neurology, the Chiari malformation (/ k i ˈ ɑː r i / kee-AR-ee; CM) is a structural defect in the cerebellum, characterized by a downward displacement of one or both cerebellar tonsils through the foramen magnum (the opening at the base of the skull).
The cerebellar tonsil (Latin: tonsilla cerebelli) is a paired rounded lobule on the undersurface of each cerebellar hemisphere, continuous medially with the uvula of the cerebellar vermis and superiorly by the flocculonodular lobe. Synonyms include: tonsilla cerebelli, amygdala cerebelli, the latter of which is not to be confused with the ...
Rhombencephalosynapsis is an anomaly characterized by the absence or severe dysgenesis of the cerebellar vermis with fusion of the cerebellar hemispheres, peduncles, and dentate nuclei. Diagnostic features include fusion of the midbrain colliculi , hydrocephalus , absence of the corpus callosum other midline structural brain malformations.
The currently accepted radiographic definition for a Chiari malformation is that cerebellar tonsils lie at least 5mm below the level of the foramen magnum. Some clinicians have reported that some patients appear to experience symptoms consistent with a Chiari malformation without radiographic evidence of tonsillar herniation.
Such cerebellar tonsil herniation may occur in up to 70% of children with M-CM. [citation needed] The medical literature suggests that there is a risk of cardiac arrhythmias in early childhood. [8] [9] The cause for this is unknown. In addition, a variety of different congenital cardiac malformations have been reported in a small number of ...
The metencephalon is composed of the pons and the cerebellum; it contains: a portion of the fourth (IV) ventricle, ... a rare cerebellar anomaly".
The cerebellum is the section of the brain that is essential for motor control. As a part of the cerebellum, the flocculus plays a part in the vestibulo-ocular reflex system, a system that controls the movement of the eye in coordination with movements of the head. [ 1 ]
Rhombencephalosynapsis is a rare brain disorder of malformation of the cerebellum that may be detected on ultrasound of the fetus. The vermis is either absent or partially formed. There is dorsal fusion of the cerebellar hemispheres, fusion of the dentate nuclei, and fusion of the middle cerebellar peduncles. [1]