Environmental factors and risk of acoustic neuroma

The aim of this thesis was to increase the knowledge about environmental risk factors of acoustic neuroma and to increase the understanding of the methodological problems encountered when studying this tumor. Acoustic neuroma is a benign, usually slow growing, intracranial tumor of the vestibulocochlear nerve (cranial nerve VIII), the nerve that transmits information about hearing and balance from the inner ear to the brain. Acoustic neuroma is usually not life threatening, the most common symptoms are unilateral hearing loss and balance problems, but more severe symptoms like hydrocephalus may occur because of its intracranial location. Very little is known about acoustic neuroma etiology. The only well-established environmental risk factor is ionizing radiation, but associations have been observed with non-smoking, income, and education. This thesis includes studies that investigated the associations between acoustic neuroma and mobile and cordless phone use, occupational and leisure time exposure to loud noise, and occupational exposure to chemical agents. In addition, a validation of self-reported start year of mobile phone use was performed, using operator data as gold standard. The thesis is based on a Swedish nationwide population based case- control study of acoustic neuroma risk factors. The study includes 451 cases of acoustic neuroma and 710 controls, matched on age, sex and residential region. Postal questionnaires were used to collect exposure information about environmental and lifestyle factors. No evidence was found for an association between use of mobile phones and acoustic neuroma risk. Odds ratios for regular use and for long-term use of mobile phones were close to unity. An elevated odds ratio was found for the highest quartile of lifetime cumulative duration of calls but no corresponding increase in the highest quartile of cumulative number of calls. An association was found for regular use of cordless phones, but not for long term use. Also for cordless phones an increased odds ratio was found in the highest quartile of cumulative duration of calls but not for number of calls. The increased odds ratios were confined to cases without histological confirmation of the tumor, which may indicate that mobile and cordless phone use increases the probability of detection of the acoustic neuroma tumors. Odds ratios were generally higher for mobile phone use on the non-tumor side of the head and the laterality analyses indicated that laterality specific analyses suffered from reversed causality as cases changed the preferred side of use because of hearing loss on the tumor side. The validation showed large random errors in the self-reported information about start year of mobile phone use. Associations were found between acoustic neuroma and exposure to leisure time loud noise, but not with occupational noise, and associations were found for occupational exposure benzene, diesel engine exhaust, gasoline, and methylene chloride