Hearing Aid for VHL Patients

with Bilateral Endolymphatic Sac Tumors

-- Nicolaos Marangos, M.D., Gerd Kempermann, M.D., Hartmut P.H. Neumann, M.D.¹

A very rare tumor which grows in the inner ear, the endolymphatic sac tumor (ELST), can cause deafness in patients with VHL. A major difficulty with this type of deafness is that it cannot be treated with usual hearing aids, because these require that the structures of the inner ear be intact. However, in recent years a novel surgical strategy has been developed that enables doctors to restore hearing in patients with inner ear damage. Although deafness due to bilateral inner ear tumors appears to be very rare, we would like to inform the community of VHL patients about this promising therapeutic strategy.

Like waves on a lake, sound is waves of the air surrounding us. There is no sound in the vacuum of interstellar space. In order to hear, our ear has to convert the mechanical energy that underlies these waves into the excitation of nerves. The outer ear funnels the sound to the eardrum which seals the middle ear. Arriving sound makes the eardrum vibrate, and the delicate chain of the middle ear transfers these vibrations to the fluid filled cavities of the inner ear. Here the actual transformation takes place. Specialized receptor cells, the so-called hair-cells, convert the mechanical energy into an electrical impulse that travels along the auditory nerve to the brain, where the incoming information is decoded. From this anatomical structure the different types of deafness are easily understood. If the outer ear canal is blocked we do not hear well, but after removal of the obstacle hearing is fully restored because the essential structures are not damaged.

If the middle ear is damaged, the transformation of waves in the air to waves on the inner ear fluids is interrupted. Here, conventional hearing aids which amplify the incoming sound so that it directly affects the inner ear fluids can help the patients. In other cases a skillful surgeon can restore the chain of middle ear ossicles and thus reestablish the interrupted connection. However, if the inner ear is damaged none of these techniques will help, because it is the receptor cells themselves that are damaged.

In recent years a new technique has been developed which bypasses middle and even inner ear function. It enables patients with inner ear damage to understand speech without lipreading. A tiny microphone is permanently placed in the vicinity of the patient's ear and a surgically implanted cable runs past the middle and inner ear directly to the beginning of the auditory nerve. Neural excitation is basically an electrical excitation with an electric discharge traveling along the nerve and carrying the information. It is possible to stimulate a nerve directly with an electric current. An ingenious concept ensures that the correct nerve cells receive the correct bits of sound information. This device is called a "cochlear implant" because it is implanted in that part of the inner ear which is named the cochlea.

Patients with VHL in rare instances develop tumors of another inner ear structure, the endolymphatic sac. Because these endolymphatic sac tumors (ELST) grow so close to the cochlea, the hair cells are easily damaged. Surgical removal of the tumor can also destroy hair cells in the cochlea. However, the auditory nerve which travels from the cochlea to the brain usually remains intact. Therefore VHL patients who encounter deafness due to ELST are considered promising candidates for cochlear implantation. Even in those extremely rare situations where the tumors or the surgical procedure necessary to remove them did affect the auditory nerve, help might be possible. An even more intricate device has been developed which stimulates the nerve cells not at the site of the cochlea but directly in the brainstem, where the auditory nerve enters the brain. Although hearing with such a "brainstem implant" is rather coarse, the technique is promising and those patients that have been treated with it report that it is very useful for oral communication if combined with lipreading.

In cases of bilateral ELST causing deafness, the option of cochlear or brainstem implants should be considered and discussed before tumor surgery. Thorough examination can differentiate between damage to the receptor cells or the auditory nerve. The auditory nerve must be preserved during surgical removal of the tumor. In many cases it will then be possible to restore or retain hearing abilities.

1. Departments of Otolaryngology and Internal Medicine, University of Freiburg, Germany (NM and HPHN) and Laboratory of Genetics, Salk Institute for Biological Studies, La Jolla, California (GK)

References: G. Kempermann, HPH Neumann, R. Scheremet, B. Volk, W. Mann, J. Gilsbach, and R. Laszig, "Deafness due to Bilateral Endolymphatic Sac Tumors in a case of von Hippel-Lindau Syndrome." Journal of Neurology, Neurosurgery, and Psychiatry (1996) 61:318-320.

As published in the VHL Family Forum, 4:4, December 1996. For permission to reprint, please contact the VHL Family Alliance, editor@vhl.org. Further information is available from the VHL Family Alliance, info@vhl.org.