Otitis media and otitis interna are defined as inflammation within the middle and inner ear. There are a variety of causes such as bacteria, fungi, yeast, parasites, foreign object, trauma, polyps and cancer.

Otitis media and otitis interna are usually caused by an extension of an external ear infection. It has been estimated that 50 percent of chronic external ear infections progress to middle ear infections.

Inner ear infections are usually a progression from middle ear infections but can develop from the spread of bacteria through the bloodstream. In these cases, an inner ear infection may not be associated with a middle or external ear infection.

Causes

The most common cause of otitis media/interna is bacteria. Various bacterial agents have been recognized in middle/inner ear infections.

Fungi and yeast are common causes of external ear infections but are not commonly found in the middle/inner ear. Malassezia, Aspergillus and Candida are some fungi/yeast involved in ear infections.

The most common parasite is the ear mite, which is usually associated with middle/inner ear infections in cats.

Foreign objects usually only affect one ear. Plant or grass awns are commonly the cause, but other foreign objects such as fleas, small insects or grass can also cause middle/inner ear inflammation.

Trauma is not a common cause since the middle and inner ear are well protected with a bony covering.

Polyps can originate in the middle ear, push through the eardrum and can be seen in the external ear canal.

Various types of cancer have been found in the middle and inner ear. For the middle ear, squamous cell carcinoma, fibrosarcoma and lymphoma are most common. For the inner ear, neurofibrosarcoma, meningioma and carcinoma are possible.