abnormal conotruncal ridge morphology conotruncal ridge hypoplasia outflow tract cushion hypoplasia csmith aortico-pulmonary spiral ridge hypoplasia MP:0010587 2010-10-05T02:26:38Z MPheno.ontology underdevelopment or reduced size of the pair of spiral mesenchymal swellings in the primordial ventricular outflow tract, that eventually fuse to form the conotruncal septum, dividing the subvalvular outflow tract and contributing to the membranous interventricular septum bulbar ridge hypoplasia conotruncal cushion hypoplasia