In virtually every case, when people discuss tinnitus (i.e. ringing in the ears) they are referring to subjective tinnitus. Subjective tinnitus is a sound that one hears that is not being caused by an external source and that cannot be heard by anyone other than the person who is suffering from the peculiar symptom. However, the term tinnitus simply means the perception of sound that does not originate outside of the body, derived from the Latin tinnire, which means “to ring.” The other form of tinnitus, called objective tinnitus, is a ringing that does not originate outside of the body (just like subjective tinnitus) but that can be heard by a careful observer. In other words, in cases of objective tinnitus, the body is making a sound, albeit very faint, that is heard by both the patient and the examiner.

A brief hearing lesson

To be sure, the great majority of tinnitus cases are considered subjective. Despite a clinician’s best efforts, no sound can be heard emanating from the affected patient. How can this be? Well as you would imagine, the auditory system (hearing system) is quite complex. First, sound waves must be captured and funneled into the ear canal. This is why we have ears at all, really. Next the collected sound waves begin their conversion from pressure waves to mechanical energy by striking the eardrum. The vibrating eardrum moves three tiny bones in the middle ear, the malleus (hammer), incus (anvil), and stapes (stirrup). Incidentally the names are derived from what the bones look like, not what they do in the ear. What these bones do is to transmit the vibrations from the eardrum to the cochlea. The cochlea is tasked with converting mechanical energy into electrical impulses, which can then be interpreted by the brain as sound. The tiny bones of the middle ear move the fluid inside the cochlea, which it turn moves tiny hair cells. When tiny hair cells are moved, impulses are sent by the eighth cranial nerve to the brain.

Subjective tinnitus

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If you could take a microscopically small broom and silently brush along someone’s hair cells, the cochlea would tell the brain that the ear was hearing sound. Likewise, it you could take an ultra-small pair of tweezers and wiggle the tiny bones in the middle ear, the brain would again perceive a sound. It is in these places that subjective tinnitus is believed to originate.

Consider the causes of subjective tinnitus; they are not things that actually cause sound. One such cause is hearing loss itself. Patients that suffer from sensorineural hearing loss often also suffer from subjective tinnitus. As the hair cells are providing less and less input to the brain, it is believed that the brain actually overcompensates for this loss of electrical information and stimulates regions of the brain that perceive sound. In essence, while actual sounds become harder to hear, the nerves create a false sound in its place. Unfortunately the result is an even greater deafness, in most cases.

Meniere’s disease is another example of a cause of subjective tinnitus. Excess fluid and pressure in the structures of the inner ear can cause fullness and ringing in the ears. There is nothing about this process that can be heard by an outside observer, but the patient perceives sound nonetheless. Likewise, benign tumors on the cranial nerve connecting the cochlea to the sensory cortex (brain) can pinch the nerve itself. This causes false electrical signals that are perceived as actual sounds (to the patient). Hormonal changes, head trauma, and certain drugs are capable of causing severe are prolonged subjective tinnitus without making a single, objective sound.

Objective tinnitus

Objective tinnitus, on the other hand, is caused by things that can be heard by the examining physician. The causes of objective tinnitus are of course different than subjective tinnitus because the source needs to be physically capable of producing sound waves. The causes of objective tinnitus are primarily those things that cause faint sounds to the observer but potentially loud sounds to the sufferer. These include muscular diseases or vascular (blood vessel) diseases, essentially.

Vascular causes of objective tinnitus

The vascular causes of objective tinnitus are slightly easier to understand. Since blood vessels are carrying blood through them at a relatively high rate of speed, it is not giant leap to imagine a blood vessel near the eardrum whooshing loud enough to make an audible sound. In fact many of us are likely to have experienced a brief bout of tinnitus after strenuous physical exercise or a powerful emotional experience that caused blood pressure to increase. However in cases of prolonged vascular objective tinnitus, the offending blood vessel is usually abnormal in some way. The blood vessel could be distended (swollen) due to long standing high blood pressure. It could have weakened arterial walls as occurs in arteriosclerosis/atherosclerosis. While new blood vessels can occur anywhere in the body, when they grow near the eardrum they can be a cause of objective tinnitus.

One rare and unfortunate reason for the growth of new blood vessels near the ear is to supply blood to a tumor. Tumors, just like any human tissue, need blood in order to survive. Since the arteries that form in and around tumors are abnormal to begin with, when they occur in the ear, head, or neck they are quite capable of creating a noise. This noise is usually constant—as constant as the beating of the heart. A small microphone placed in the patient’s ear would allow the observer to hear the tinnitus-causing sound. Again, this form of tinnitus is rare, but is an illustrative example of objective tinnitus.

Muscular causes of objective tinnitus

Abnormalities in the muscles near the ear can cause objective tinnitus. One example is the case of amyotrophic lateral sclerosis (ALS Lou Gehrig’s disease). In this degenerative disease, the nerves that normally supply muscles die. The muscles that were supplied by those dying dead nerves will then atrophy. A muscle that is undergoing atrophy experiences tiny tremors called fasciculations. If you have fasciculations close to the auditory system, it can be heard as a sound. Other muscular causes of objective tinnitus are things that cause abnormal muscle movement, such as spasms. In fact, a muscle spasm in the stapedius muscle (attached to the small stapes bone in the middle ear) is known to cause objective tinnitus.

Clarifying objective tinnitus and subjective tinnitus

It should be mentioned that in some (even many) cases of objective tinnitus, the physician or other examiner will not be able to actually hear the sound that is being heard by the patient. This does not necessarily change the diagnosis to subjective tinnitus. Rather, the label of objective tinnitus versus subjective tinnitus is generally based on the cause of the abnormal sound, not whether it can be heard by the observer. In other words, if the tinnitus is being caused by something that could theoretically be heard, like blood whooshing through a blood vessel, it could be classified as objective tinnitus. On the other hand, if the cause is something that could not possibly be heard by someone other than the patient, like in Meniere’s disease, then it is classified as subjective tinnitus.