cochlear ganglion hypoplasia underdevelopment or reduced size, usually due to a reduced number of cells, of the group of nerve cell bodies that conveys auditory sensation from the organ of Corti to the hindbrain and resides on the cochlear part of the vestibulocochlear nerve (eighth cranial nerve) MP:0003637 MPheno.ontology spiral ganglion hypoplasia reduced number of spiral ganglion cells small cochlear ganglion