Congenital sensorineural hearing loss and ABI surgery: preoperative radiological protocol and considerations after 12 years of experience

Purpose: Cochlear nerves aplasia represents a rare but possible congenital cause of Sensori Neural Hearing Loss (SNHL) in children. Early identification and accurate diagnosis are mandatory to correctly select auditory brainstem implantation (ABI) candidates. The purpose of the study was to evaluate the contribution of a complete pre-operative radiological assessment based on CT and MRI to prevent misdiagnosis and erroneous treatments. Methods and Materials: Since 2000, 38 SNHL patients have been treated with an ABI in our ENT Department. Six patients had already been operated elsewhere with cochlear implantation without benefits. All the children performed pre-operative functional tests, temporal bone CT and brain/cerebellum-pontine angle (CPA) MRI. Results: MRI showed in all cases the absence of the cochlear branch of the eighth nerve bilaterally (38/38). Unilateral facial nerve aplasia was present in one patient. Associated inner ear malformations were present in 21/38 patients, in particular common cavity in 8/21, incomplete partition type 1 in 6/21 and semicircular canals malformations in 3/21. No brain anomalies were showed. CT scans better depicted the labyrinthine malformations, adding information about facial nerve canal and internal auditory canal (IAC) size. 2/38 CT showed normal inner ear structures and IAC size. Conclusion: Providing accurate information about cochlear nerve and brain anomalies is crucial in the pre-operative assessment of SNHL patients. MRI is the only radiological technique that is able to directly demonstrate the presence or the absence of cochlear nerves. CT is not fundamental and provides complementary information; a negative CT pattern cannot exclude a cochlear nerve malformation.