= characterized by absence of vermis + continuity of cerebellar hemispheres, dentate nuclei, superior cerebellar peduncles

Associated with: Gómez-López-Hernández syndrome (parietal alopecia, trigeminal anesthesia, craniofacial dysmorphic signs); VACTERL

• truncal ± limb ataxia, delayed motor development
• abnormal eye movements
• agenesis or hypogenesis of vermis
• keyhole-shaped fourth ventricle ← horseshoe-shaped arch across midline ← fusion (continuity) of cerebellar hemispheres + superior cerebellar peduncles + dentate nuclei
  • abnormal transverse orientation of cerebellar foliae

Prognosis: varying between severe impairment and normalcy