Tinnitus is not a disease in and of itself, but rather a symptom of some other underlying health condition. In most cases, tinnitus is a sensorineural reaction in the brain to damage in the ear and auditory system. While tinnitus is often associated with hearing loss, there are roughly 200 different health disorders that can generate tinnitus as a symptom. Below is a list of some of the most commonly reported catalysts for tinnitus.
About 25-30 million Americans have tinnitus as a condition, and they experience these noises on a regular, most often daily, basis. About 40 percent of people with tinnitus hear tinnitus noise through 80 percent of their day. And for a smaller group of people—about 1 in 5, tinnitus is disruptive enough to significantly interfere with daily functioning, becoming disabling or nearly disabling.
Tinnitus is when people think they hear something in their ears but there is actually no sound. People with tinnitus actually do "hear" noises that range from a whistle to a crackling noise to a roar. It can happen only occasionally, can occur for a period of days then take a break before recurring again, or it can be constant. The sound can vary in pitch from quiet to unbearably loud, or it can stay the same.

Traumatic brain injury, caused by concussive shock, can damage the brain’s auditory processing areas and generate tinnitus symptoms. TBI is one of the major catalysts for tinnitus in military and veteran populations. Nearly 60% of all tinnitus cases diagnosed by the U.S. Veterans Administration are attributable to mild-to-severe traumatic brain injuries.
MRI (or magnetic resonance imaging) scan is a radiology technique which uses magnetism, radio waves, and a computer to produce images of body structures. MRI scanning is painless and does not involve X-ray radiation. Patients with heart pacemakers, metal implants, or metal chips or clips in or around the eyes cannot be scanned with MRI because of the effect of the magnet.

But it’s still a significant improvement. And Kilgard says he and others are working to make the treatment even more effective. He suspects this type of therapy is not too far off from being available to patients outside of research studies. “It’s in the late stages of development,” he says. “It could be available to the public in as little as a year or two.”
Supporting the idea that central reorganization is overestimated as "the" cause of tinnitus, a recent study by Wineland et al showed no changes in central connectivity of auditory cortex or other key cortical regions (Wineland et al, 2012). Considering other parts of the brain, Ueyama et al (2013) reported that there was increased fMRI activity in the bilateral rectus gyri, as well as cingulate gyri correlating with distress. Loudness was correlated with values in the thalamus, bilateral hippocampus and left caudate. In other words, the changes in the brain associated with tinnitus seem to be associated with emotional reaction (e.g. cingulate), and input systems (e.g. thalamus). There are a few areas whose role is not so obvious (e.g. caudate). This makes a more sense than the Wineland result, but of course, they were measuring different things. MRI studies related to audition or dizziness must be interpreted with great caution as the magnetic field of the MRI stimulates the inner ear, and because MRI scanners are noisy.

Paquette et al (2017) reported a prospective study of 166 patients who had brain surgery involving removal of the medial temporal lobe. The prevalence of tinnitus increased from approximately from 10 to 20% post surgery. This study did not include a control -- a natural question would be -- suppose a different part of the brain were removed. One would also think that drilling of the skull from any source might increase tinnitus. We are presently dubious that the medial temporal lobe suppresses tinnitus.
Other causes of tinnitus include middle ear infections, disorders that block the ear canal (such as an external ear infection [external otitis], excessive ear wax, or foreign bodies), problems with the eustachian tube (which connects the middle ear and the back of the nose) due to allergies or other causes of obstruction, otosclerosis (a disorder of excess bone growth in the middle ear), and temporomandibular disorders. An uncommon but serious cause is an acoustic neuroma, a noncancerous (benign) tumor of part of the nerve leading from the inner ear.
Although there’s no proven cure for tinnitus, there are treatments that help make it easier to ignore. For example, you can wear devices in your ear(s) that produce soothing therapeutic noises to shift your focus away from the tinnitus. Other devices produce constant, soft noise to mask the tinnitus. Tinnitus sufferers who also have hearing loss sometimes find relief simply by wearing properly fitted hearing aids.