“Tectal beaking” is MRI feature of:

Arnold Chiari I malformation Chiari 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  0–10 years à 6 mm at least 10–30 years à 5 mm  30–40 years à 4 mm Associated anomalies: Syringomyelia (30–60%), hydrocephalus (20–25%), basilar invaginations (25–50%), Klippel-Feil syndrome (5–10%) and atlanto-occipital assimilation (1–5%) Chiari 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: