Cochlear hypoplasia is a group of inner ear malformations defined by a smaller than normal cochlea with various internal architectural abnormalities such as having <2 turns.
Cochlear hypoplasia accounts for 15% of cochlear malformations .
According to the classification of Sennaroglu, there are four radiographically defined types of cochlear hypoplasia . In each type, the cochlea is a structure located at the end of the internal auditory canal, lucent on CT and fluid signal on MRI, that is overall smaller than normal.
- CH-I: bud-like cochlea
- round/ovoid and small cochlea, with absent modiolus and interscalar septa
- CH-II: cystic hypoplastic cochlea
- similar external shape to a normal cochlea but smaller, with defective modiolus and interscalar septa
- CH-III: cochlea with <2 turns
- similar external shape to a normal cochlea but shorter and fewer turns, with present but short modiolus and reduced total length of the interscalar septum
- CH-IV: cochlea with hypoplastic middle and apical turns
- normal basal turn but small middle and apical turns located more anterior and medial than normal
Additional extracochlear findings are variably associated:
- cochlear nerve often hypoplastic or absent
- cochlear nerve canal: absent, narrow or normal
- vestibule and semicircular canals are usually malformed but may be normal
- internal auditory canal: normal or narrow
- vestibular aqueduct: normal or large
- incomplete partition also features abnormal internal architecture of the cochlear and clear differentiation from the vestibule, but the cochlea has a normal-sized external contour