“Sudden hearing loss” means   a single or bilateral perceptual deafness usually of relevant importance,  with sudden onset and unknown etiology.
The audiometric criterion accredited today to define  sudden deafness   is the relief of an auditory loss of more than 30 dB, in at least three contiguous frequencies.
Hearing loss can be  of varying   size up to complete anacusia.
The incidence of sudden hearing loss is    5-20 cases per 100,000 inhabitants per year. 75% of cases occur after the age of 40;  is considered  rare in the child. There is no difference between the sexes. 40% of cases are bilateral and, of these, only 50% are contemporary.
The high percentage of spontaneous healing causes  the actual incidence to be underestimated.
Although itsorigin is unknown, the main ethyopathogenic  hypotheses  can be grouped into three categories:
1. Viral theory: Many authors believe that sudden hearing loss is the result of a viral infection affecting the cochlea or acoustic nerve. This theory is based on the fact that sudden hearing loss is   often preceded by flu syndrome (up to 30-40 percent of cases). This hypothesis  was  confirmed by  Schuknecht,who studied 12 temporal bones of patients who had presented sudden deafness in life.  Degenerative alterations of the corti organ similar to those encountered in viral labyrinthitis caused by mumps virus, CMV, herpes zoster, rubella and HIV were observed in these patients.
2. Vascular theory: it is based on a phenomenon common to other vascular pathologies, in which a labyrinthine ischemia occurs when the blood flow of the internal auditory artery occurs. For this reason sudden hearing loss would be  more frequent in patients with cardiovascular risk factors (thromboembolic disease,  states of hypercoagulation,  dyslipemia,diabetes mellitus).
3. Mechanical theory: it is based on the hypothesis that sudden hearing loss is caused by the rupture of the oval window membrane or round window. This event could be caused by a sharp pressure difference between perilinfa and crate, as is the case in barotraums or sudden efforts that result in an increase in pressure in the liquor and perilinfa.
Clinically it is a neurosensory hearing loss that is rapidly established, often of great intensity  (anacusia  in 10-20 percent of cases), sometimes bilateral, which is often accompanied by tinnitus and sometimes dizziness. Tinnitus are present in 70% of cases, being able to precede hearing loss up to 25% of cases.  There is a feeling of ear impairment and vestibular symptoms may be present, which appear in 50% of cases (from a feeling of insetiness,40% of cases, to intense vertigo, 10% of cases).
The diagnosis makes use of clinical exploration with otoscopy, which   is normally negative but previous chronic pathologies of the middle ear and tympanic membrane may coexist. Pathology of the outer ear (earwax caps) and middle ear (acute otitis media) should be excluded. Subsequently, a liminar tonal audiometry should be carried out (which shows a unilateral or bilateral neurosensory hearing loss, with various types of audiometric, pantonal, uphill or downhill curve. According to many studies,      the most frequent hearing loss is pantonal, followed by downhill hearing loss), impedenzometry (which shows a normal tympanogram: Jerger’s type A), auditory evoked potentials (ABR: useful to exclude  retrocal pathology ctorMRI (necessary to exclude tumor pathology of the pontocerebellarangle) and laboratorytests (to exclude systemic pathologies that can cause sudden deafness  (autoimmunitary diseases or alterations of blood crasis).
As far as prognosis is known, according to some authors, 33% of cases recover without treatment. The presence of vestibular signs (imbalance, dizziness) is  associated with a worse prognosis. Generally, the worse  the initial hearing loss, the worse the  prognosis.  The uphill or pantonal liminar tonal audiometric curve has a better prognosis (hearing recovery up to 90 percent of cases), the liminar tonal audiometric curve downhill, with loss in acute tones, has a worse prognosis with recovery in about 30 percent of cases. In patients over  40, the prognosis  is   worse. The  precociation  of treatment  is essential in order to obtain a recovery of hearing function: sudden deafness  is, therefore, a real urgency. According to international literature, therapy can  only be  effective if started before 24, maximum 72 hours.