The ear is made up of three parts: external, middle and inner. The external consists of the part of the ear we see, including the canal . The middle ear consists of the ear drum and three very small bones: the malleus, the incus and the stapes. As sound strikes the ear drum, it vibrates and transmits these vibrations to the tiny bones, which in turn amplify the vibrations. The inner ear consists of the cochlea (a snail-shaped organ which is very essential to hearing), vestibules, and semi-circular canals. As the stapes moves, it produces fluid waves within the cochlea. The waves cause tiny hair-like cells within the cochlea to vibrate, which in turn send signals to the brain which can then be interpreted as sound. The semi-circular canals help the body maintain its sense of balance.
Mondini dysplasia (malformation) is a condition of the inner ear in which the cochlea has only one and one-half turns instead of the usual 2 and one-half, large vestibule (cavity), abnormal or missing semi-circular canals, bulbous (enlarged) endolymphatic duct and sac, and immature senorineural structures. The degree of hearing loss depends on the extent of changes that occurred in the various structures of the cochlea.
In very general terms, we can divide the act of hearing into two parts: the peripheral hearing system and the central hearing system.
The peripheral system consists of the external , middle, and inner ear. Any disorder or disease that occurs in the external or middle ear may result in a conductive hearing loss. As the name implies, sound will not be conducted through the hearing mechanism accurately. Examples of this would be otitis media (middle ear infection) and malformed ossicles (those 3 tiny bones) that are sometimes seen in Kabuki Syndrome. Conductive hearing problems are often helped with medication or surgery. When the damage is located in the inner ear, we then refer to this as a sensorineural hearing loss. So, in this case the sound is "conducted" properly through the outer and middle ear but is diminshed upon reaching the inner ear defect, as for example would be the case with Mondini dyplasia. Generally speaking, sensorineural hearing loss is usually not helped by medication or surgery. People with this type of hearing impairment are assisted through the use of hearing aids and other assistive listening devices. Perhaps, in some instances they may be candidates for cochlear implants.
The central hearing system (also called central auditory nervous system) begins at the point when the nerve enters the brain stem. It is here that sound is processed and interpreted.
Inner Ear Abnormalities in Kabuki Make-Up Syndrome: Report of Three Cases - American Journal of Medical Genetics May 15;92(2) pp. 87-9 2000 Author: Igawa HH, Nishizawa N, Sugihara T, Inuyama Y.
Three cases were presented: a 28 year old female (patient 1), a 15 year old male (patient 2), and a 14 year old male (patient 3). Computerized tomography (CT) scans were taken to view the petrous bones of the external auditory canal, middle and inner ears of all patients and a Standard Audiometric test was performed on patients 1 and 2 (patient 3 did not co-operate).
The CT scan revealed *Mondini dysplasia in both ears of all three patients. The cochlea were flattened with only one or one-half turns, the vestibules were dilated and the semi-circular canals were deformed. The external canals and middle ears showed no abnormalities. Audiograms of patients 1 and 2 revealed *sensorineural high tone loss of hearing over 2000Hz in both ears in patient 2 and in right ear of patient 1.
In many of the past reviews hearing loss was thought to have occurred because of frequent ear infections. These findings indicate inner ear abnormalities as a mechanism causing hearing impairment. It's advised that CT scanning of the petrous bones and audiometry is done for children diagnosed with Kabuki. Early detection of inner ear abnormalities would lead to early preventative management of possible complications and use of hearing aids.
I would like to thank the following professionals for their assistance:
Dr. Edmond Lemire, MD, PhD, FRCPC, FCCMG, FACMG
Wendi Stoeber, genetic counsellor
Janet Sacca, M.A./ FAA