Unpartitioned versus incompletely partitioned cochleae: radiologic differentiation.

OBJECTIVE: In the process of evaluating our patients, we realized that the term "Mondini deformity" was being used to describe two different types of incomplete partition of the cochlea. THE First one consisted of an unpartitioned, completely empty cochlea where the interscalar septum and entire modiolus were absent, giving the cochlea a cystic appearance; a grossly dilated vestibule accompanied this lesion. The second pathology fitted the classic description of Mondini deformity, consisting of a normal basal turn and cystic apex (where the middle and apical turns form a cystic cavity), dilated vestibule, and enlarged vestibular aqueduct. This study was planned to investigate the differences between the two types of incomplete partition for inner ear malformations based on radiologic features. STUDY
DESIGN: We conducted a retrospective review of temporal bone computed tomography (CT) findings.
METHODS: The subjects were 18 patients with profound bilateral sensorineural hearing loss who had high-resolution CT with contiguous 1-mm thick images obtained through the petrous bone in axial sections. The CT results were reviewed as incomplete partition type I (IP-I) and type II (IP-II). Incomplete partition type I (unpartitioned cochlea, cystic cochleovestibular malformation) is defined as a malformation in which the cochlea lacks the entire modiolus and interscalar septa, resulting in a cystic appearance and there is an accompanying grossly dilated vestibule. In incomplete partition type II (incompletely partitioned cochlea, the Mondini deformity), there is a cochlea comprised of a normal basal turn and cystic apex accompanied by a minimally dilated vestibule and enlarged vestibular aqueduct (VA). Measurements involving the cochlea, vestibule, vestibular aqueduct, and internal auditory canal (IAC) were done to determine the characteristic features of these pathologies.
RESULTS: : Thirteen ears had IP-I and 18 ears had IP-II anomaly. The size of the cochleae in both anomalies showed no significant difference from the normal findings. Only the internal architecture was different. All ears with IP-I had grossly dilated vestibules. Although both anomalies demonstrated vestibular dilatation, the degree of that was minimal in patients with IP-II. In IP-I anomalies, the IAC was larger than that in IP-II anomalies. An enlarged VA accompanied all cases of IP-II, whereas only one of the patients with IP-I had VA that could be demonstrated on CT. In all cases, the VA findings were symmetric on both sides: normal or enlarged.
CONCLUSION: Inner ear measurements on radiologic findings in this study confirmed the presence of two different types of incomplete partition: IP-I (unpartitioned cochlea, cystic cochleovestibular malformation) and IP-II (incompletely partitioned cochlea, the classic Mondini deformity). The type I malformation is less differentiated than the type II malformation. Classic Mondini deformity has three components (a cystic apex, dilated vestibule, and large vestibular aqueduct), whereas type I malformation has an empty, unpartitioned cochlea and dilated vestibule without an enlarged VA. Mondini deformity represents a later malformation, so the degree of dysplasia is milder than that in type I. Not only the appearance, but also the measurements of the inner ear structures would be helpful in determining the type of malformation.