<prompt> Tectal beaking is MRI feature of:Dandy Walker malformationArnold-Chiari malformationAqueductal stenosisThird ventricular tumor  <response>: Arnold Chiari I malformationChiari I malformation cerebellar ectopia and seen in adulthood.Definition: - Descent of otherwise normal cerebellar hemispheres below the foramen magnum, usually involving tonsils.Features: Peg like, pointed tonsils displaced into upper cervical canal 010 years à 6 mm at least1030 years à 5 mm 3040 years à 4 mmAssociated anomalies: Syringomyelia 3060, hydrocephalus 2025, basilar invaginations 2550, Klippel-Feil syndrome 510 and atlanto-occipital assimilation 15Chiari II malformation childhood.Definition: Descent of dysplastic cerebellar hemisphere below the foramen magnum, usually involving inferior vermis, which is everted instead being inverted, causing 4th ventricle to reduce to a coronal cleft and medulla oblongata to elongate and kink.Features: 