A staphylococcal abscess arising from the base of a hair follicle, commonly referred to as a "boil".
Furuncles can only occur in the outer cartilaginous part of the ear canal, since the skin of the inner two thirds of the canal is hairless.
Furuncles usually result from the entry of pyogenic staphylococci into the skin of the superficial externa canal.
Since the skin of the external canal is adherent to the underlying perichondrium, even a small furuncle will produce severe local pain, which is aggravated by movement of the pinna, pressure on the tragus or even chewing. Hearing loss is unusual but may be present if the external canal is occluded either by a large solitary furuncle or by edema.
An extremely tender erythematous (red) localized swelling located in the outer hairbearing portion of the external canal is typically seen.
It should be noted that a small furuncle may be missed on otoscopic examination if the aural speculum is inserted too deeply.
When examining the ear, care must be taken always to examine the superficial part of the canal.
The tympanic membrane is not involved in this condition; however, if the tympanic membrane cannot be inspected, either because it is obscured by a large furuncle or if the patient experiences such pain on examination that the speculum cannot be advanced into the deep meatus, the examiner must then consider all other causes of acute inflammatory ear disease, such as otitis media or mastoiditis.
Enlargement of the lymph nodes between the mandible and the mastoid and pain on moving the tragus are common in furunculosis but are extremely unusual in middle ear infections.
A large, painful, pointing furuncle is visible on the posteroinferior canal wall.