Mechanisms of subjective tinnitus

The inner ear contains many thousand minute hairs which vibrate in response to sound waves. Receptor cells (hair cells) in turn send signals to the brain which are interpreted as sound. Although receptor cells can be regenerated from the adjacent supporting Deiters cells after injury in birds, reptiles, and amphibians, in mammals it is believed that they can be produced only during embryogenesis. Although mammalian Deiters cells reproduce and position themselves appropriately for regeneration, they have not been observed to transdifferentiate into receptor cells except in tissue culture experiments.Therefore, if these hairs become damaged, through prolonged exposure to excessive volume, for instance, then deafness to certain frequencies occurs. In tinnitus, they may falsely relay information at a certain frequency that an externally audible sound is present, when it is not.

The mechanisms of subjective tinnitus are often obscure. While it's not surprising that direct trauma to the inner ear can cause tinnitus, other apparent causes (e.g., TMJ and dental disorders) are difficult to explain. Recent research has proposed that there are two distinct categories of subjective tinnitus, otic tinnitus caused by disorders of the inner ear or the acoustic nerve, and somatic tinnitus caused by disorders outside the ear and nerve, but still within the head or neck. It is further hypothesized that somatic tinnitus may be due to "central crosstalk" within the brain, as certain head and neck nerves enter the brain near regions known to be involved in hearing.

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Pulsatile Tinnitus

In this form of tinnitus the sufferer hears something resembling their heartbeat in their ear. The cause for pulsatile tinnitus usually involves vascular, tumor or muscular causes. A blood vessel may be close to the eardrum, a vascular tumor such as a "glomus" may fill the middle ear, or a vein similar to a varicose vein may make enough noise to be heard. Other pulsatile tinnitus possibilities include dehiscence of the jugular bulb, and an abberently located carotid artery. An enlarged jugular bulb on the involved side is common in persons with venous type pulsatile tinintus.

In persons with pulsatile tinnitus, additional tests may be proposed to study the blood vessels and to check the pressure inside the head. Gentle pressure on the neck can be performed to block the jugular vein but not the carotid artery. The Valsalva maneuver reduces venous return by increasing intrathoracic pressure. If there is a venous hum, this usually abates or improves markedly. If the pulsatile tinnitus pulsation is arterial, these tests have no effects. MRI/MRA or CT is often suggested in younger patients with unilateral pulsatile tinnitus.

In older patients, pulsatile tinnitus is often due to atherosclerotic disease and it is less important to get an MRI/MRA. In some cases of pulsatile tinnitus a lumbar puncture may be considered if there is a possibility of benign intracranial hypertension. More invasive pulsatile tinnitus testing includes the "balloon occlusion test", where a balloon is blown up in the internal jugular vein to see if it eliminates pulsatile tinnitus.

It is strongly recommended that all individuals with pulsatile tinnitus locate an excellent physician with interest in the circulatory system and complete a thorough examination. Based on research, which included reviewing 7 otolaryngology textbooks and over 250 research studies, data appears to support the underlying cause for detecting a pulsatile tinnitus as physiologic in nature. That said, there are many, many cases of pulsatile tinnitus that defy diagnosis and identification of the causative agent.

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Tinnitus Management

Tinnitus ("TIN-a-tus" or "Tin-EYE-tus"), more commonly spoken of as "ringing in the ears" or "head noise," has been experienced by almost everyone at one time or another. It is defined as the perception of sound in the head when no external sound is present.

In addition to "ringing," head noises have been described as hissing, roaring, pulsing, whooshing, chirping, whistling and clicking. Ringing and head noises can occur in one ear or both ears, and can be perceived to be occurring inside or outside the ear. It can accompany hearing loss. It can exist independent of a hearing loss.
What should I do?

Since tinnitus is a symptom of a problem, the first thing you should do is to try to find out the underlying cause. You should have a medical examination with special attention given to checking factors associated with tinnitus such as blood pressure, kidney function, medications/drug intake, diet and allergies, emotional stress, noise exposure, and diseases involving the auditory system. Tinnitus can be associated with conditions that occur at all levels of the auditory system.

Some of these conditions are impacted wax (external ear); ear infection, middle ear tumors, otosclerosis, vascular problems (middle ear); Menieres disease, ototoxic medications, circulation disorders, noise-induced hearing loss (inner ear); and, at the central level, 8 th nerve and other tumors, migraine, and epilepsy.

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