In Ménière's Disease any kind of surgery, whether vestibular nerve section, cochlear nerve section, endolymphatic sac surgery or gentamicin injections, never seems to produce greater than 50% tinnitus control - a marginal improvement upon the 30% spontaneous disappearance in its natural history.

In Otosclerosis relief of the non-pulsatile tinnitus by successful stapedectomy can be expected in about 40 to 64%.

The Chiari Malformation is a clinical entity in which there is a tonsillar herniation into the foramen magnum. 7 to 10% of these patients suffer from tinnitus and it can be both non-pulsatile and pulsatile.

The pulsatile tinnitus consists of a venous hum caused by raised intracranial pressure and worsens on bending over, but disappears on ipsilateral jugular vein compression, which also results in an improvement of the hearing (masking). No brainstem auditory evoked potential changes are noted in this kind of tinnitus. After the surgical decompression this form of tinnitus disappears.

The non-pulsatile tinnitus on the other hand is usually intermittent and the cause is not known. It is either due to stretching of the cochlear nerve, e.g. by microvascular compression, or to brainstem traction. Brainstem auditory evoked potential changes are noted in 75% of the patients and consist of an IPL III-V prolongation in 100% of the patients (brainstem traction and/or contralateral microvascular compression ?) and in 30% of IPL I-III prolongation (ipsilateral microvascular compression ?).

Posterior fossa decompression which consists of opening the foramen magnum and widening the dura mater results in abolishing the non-pulsatile tinnitus if tinnitus is of recent origin.

Arachnoid cyst is a rare cause of non-pulsatile tinnitus. It is a congenital or posttraumatic/post inflammatory disorder leading to vague symptoms. Arachnoid cysts producing tinnitus can occur in the CP angle, but also retroclival and retrocerebellar. Usually symptoms of intracranial hypertension are associated with non-pulsatile tinnitus. Surgical treatment consists of marsupialization or excision of the cyst.

Other Cerebellopontine Angle Lesions (CPA) such as meningiomas, epidermoid tumours, lipomas, choroid plexus papillomas, epithelial cysts, teratomas, cavernomas, and hemangiomas can present with non-pulsatile tinnitus, usually with associated symptoms depending on the location of the lesion and the degree of brainstem, cerebellar or cranial nerve compression.

Electrical stimulation of the auditory cortex is a new kind of treatment based on the working mechanism of how tinnitus arises. An electrically active electrode is placed on the area of cortical reorganization, ie. the zone where braincells are looking for a new job. By means of stimulating those braincells electrically they are prevented from growing into the neighbouring areas. In other words the normal internal neural stimulation of those braincells is taken over by external electrical stimulation.

In a clinical setting two problems must be solved. First of all the exact localisation on the brain of the auditory cortical reorganization has to been demonstrated. This is done by means of a functional MRI. This is a classical MRI scan where two scans are combined : a normal brainscan and a scan performed during auditory exposure.

The second problem is retrieving the zone of cortical reorganization as demonstrated on the scanner exactly on the patient' s brain. Therefore neuronavigation is used guided by the funtional MRI. The navigation system is basically a GPS system specifically adapted for brain surgery. Thus the functional MRI, demonstrating the area of the organization is put on a CD-Rom which is then inserted in the neuronavigation system similar to the map of a country or city that is being downloaded into a GPS system.

When this is ready, a non invasive way of demonstrating the efficacy of the stimulation is performed by means of transcranial magnetic stimulation guided by the navigation system. If this non invasive test is succesful in suppressing the tinnitus, at a later stage an electrode can be placed extradurally on the auditory cortical zone of reorganisation (on the exact same site as where the transcranial magnetic stimulation was successful). The electrode is activated and powered by a battery that is implanted in the abdomen. Via a remote control the stimulation parameters (frequency, amplitude and pulse width) can be changed postoperatively to find the best parameters for maximal tinnitus control.