Aplasia/Hypoplasia of the cerebellum Cerebellar agenesis 2014-01-22T08:14:57Z HP:0012642 Usually, small remnants of the cerebellum are present; therefore the term subtotal cerebellar agenesis is also used in the literature. A secondary pontine hypoplasia is typically seen. The definition of cerebellar agenesis is based on the morphologic pattern and does not suggest the pathogenesis. Cerebellar agenesis may represent a malformation (e.g., mutations in PTF1A) or a disruption (e.g., hemorrhage that occurs during gestation or in the perinatal period, vascular insufficiency in Chiari II malformation and cerebellar herniation, and as a sequela of prematurity). Cerebellar agenesis is defined by the near complete absence of cerebellar tissue with only remnants of the anterior vermis, flocculus, and/or middle cerebellar peduncles. UMLS:C4022808