Incomplete partition type I

Incomplete partition type I (IP-I) is characterized by a cochlea which lacks the entire modiolus and interscalar septa. They represent approximately 11.5% of inner ear malformations (IEM). The cochlea can be clearly differentiated from vestibular system and is located in its usual location in the anterolateral part of the internal auditory canal (IAC). Cochlea is accompanied by enlarged vestibule. This anomaly was described in 2002 and named as "cystic cochleovestibular malformation." Due to developmental abnormality of the cochlear aperture and absence of the modiolus, there is a defect between the IAC and the cochlea and cerebrospinal fluid (CSF) may completely fill the cochlea. This results in CSF gusher during cochleostomy or a recurrent meningitis through spontaneous oval window fistula. IP-I constitutes the most important etiology for recurrent meningitis in children. Cochlear nerve may be absent and this may necessitate an auditory brainstem implantation. In this chapter, radiological, audiological features, and surgical considerations of IP-I anomaly along with case presentations are provided.