Despite the fact that sensory-nervous sudden hearing loss of unknown aetiology was first described 138 years ago, this is still one of the controversial problems in otolaryngology.

According to Turmond and Amedee (16) and a number of other authors, sudden deafness means a hearing loss of at least 30dB for three consecutive frequencies occurring in a time period of less than three days. Hughes et al. (3) state that in the US there are 4000, and world-wide 15000, new cases of sudden deafness annually. According to Kog et al. (4), the incidence of unilateral sudden hearing loss in children amounts to approximately 0.1% and the aetiology of most of the cases remains unknown; neither children nor their parents can precisely determine the time of its appearance, especially when it is not accompanied by other symptoms, such as dizziness or tinnitus.

Analysing the risk factors of idiopathic sudden deafness, Nakashime et al. (6) concluded that fatigue and the influence of environmental factors, including diet, are essential in the aetiology of sudden hearing loss. Among various aetiological factors responsible for the pathomechanism of the disease, especially in adults, circulatory disorders are of primary importance (5, 9, 10, 11). On the other hand, Prirod et al. (10, 11) suggest that hypotension, especially in young children, is a fundamental factor in sudden deafness, and that in many cases after pharmacological regulation of vascular motor activity the hearing threshold easily returns to normal. The next most important factor causing sudden hearing loss is viral infection (1, 14, 18), especially epidemic parotitis (4, 12, 17). A number of cases have been reported of sudden deafness (both uni- and bilateral) in the asymptomatic course of mumps (4). This was confirmed by Okamato et al. (7) who examined the level of antibodies against epidemic parotitis in the serum of 131 patients with sudden deafness. Positive results obtained in 9 of them confirmed the relationship between sudden deafness and an asymptomatic course of mumps. Toxoplasmosis (13), disturbed iron metabolism (15) and measles (2) should also be taken into consideration as causes of sudden deafness. Nevertheless, in a great number of cases, the aetiology of idiopathic sudden hearing loss in children remains unknown (9, 8).

The aim of our study was evaluation of the influence of probable aetiological factors on the occurrence of unilateral hearing loss in children.

The study included 80 children aged 2 to 14 years hospitalized in the ENT Department of Jagiellonian University Hospital in Cracow in the last 10 years because of sudden unilateral hearing loss.

The assessment of the influence of the probable aetiological factors on unilateral deafness was carried out on the basis of:

1. Detailed history concerning the onset of deafness, concomitant diseases and symptoms, such as influenza, mumps, herpes, German measles, trauma of the head, tinnitus and dizziness, as well as other systemic diseases.

2. Physical examination including otolaryngological, pediatric and neurological examinations (when indicated).

3. Comprehensive audiological evaluation, that is, pure tone audiometry, registration of evoked otoaudiological emissions (EOAEs) and tympanometric tests.

As Table 1 shows, sudden hearing loss in the studied group occurred in 37 girls (46.25%) and 43 boys (53.75%). In 42 cases sudden unilateral deafness affected the right ear (52.5%) and in 38 cases the left ear (47.75%).

Taking into consideration the aetiological factors responsible for sudden deafness in various age groups of the children examined, most often, that is in 25 cases (31.25%) the aetiological factor remained unknown. After adding cases of unilateral deafness revealed accidentally in children mainly between 7 and 10 years of age, the amount of deafness of unknown aetiology increases by another 6 children and amounts to 31 cases (38.75%).

Among the probable aetiological factors, the primary one seems to be epidemic parotitis in 22 children (27.5%), followed by, viral influenzal infections and infections of the upper respiratory tract in 14 children (17.5%) (Tab.2). Another factor responsible for sudden deafness is trauma of the skull including fracture of the petrous pyramid in 7 children (8.75%). Other probable aetiological factors, such as German measles and meningitis, were observed in single cases only.

Evaluating the age of the children affected by sudden unilateral hearing loss, it should be stressed that children between 7 and 10 years of age are especially predisposed to this disorder - 35 cases (43.75%). In children at this age the prevailing diseases are viral infections, such as mumps, influenza and German measles, which occurred in 17 cases (21.25%). In this group of children, equally frequently, that is, in 17 cases (21.75%) the aetiological factor remained unknown. In older children, aged 11 to 14 years, the primary factor seems to be a trauma of the head with fracture of the petrous pyramid.

Assessment of the period of time from the onset of unilateral sudden hearing loss to its diagnosis and initiation of pharmacological therapy (Tab. 3) showed that within the first 7 days of sudden deafness, that is, the time essential to the effectiveness of therapy, the children who most commonly reported to the hospital were those with trauma of the skull. Two to four weeks after the onset of sudden deafness, the number of children who reported increased and amounted to 26 children (32.5%), most often after mumps or a viral infection.

A large group of 42 children (52.5%) reported one to several months after the onset of sudden hearing loss and in this group no pharmacological therapy was instituted. Further audiometry in this group, carried out during check-ups within the last 5 months, showed that the pharmacological treatment instituted in 38 (47.5%) children at the moment of admission to hospital did not improve their impaired hearing.

1. In our studies of unilateral sudden hearing loss, a significant sex predomination was not observed, however it was noted more often in boys (53.8%) than in girls (46.2%).

2. Unilateral sudden hearing loss occurred most often in children between 7 and 10 years of age, which was noted in 35 children (43.8%).

3. At this age, sudden hearing loss of unknown aetiology and hearing loss caused by epidemic parotitis were the most common.

4. Trauma of the head with fracture of the petrous pyramid causing unilateral sudden hearing loss is most often observed in children aged 11-14 years.

5. Among known aetiological factors of unilateral sudden hearing loss in children, viral infections played a predominant role in 39 children (48.8%).

6. The aetiological factor responsible for sudden deafness in the study group remained unknown in 31 cases (38.76%).