Are prior head injuries or diagnostic X-rays associated with glioma in adults? The effects of control selection bias

The causes of glioma, the most common type of primary malignant brain tumor s, are poorly understood. This study compares personal histories of head in jury and diagnostic radiation procedures of the head and neck among 476 adu lts newly diagnosed with glioma in the San Francisco Bay Area between Augus t of 1991 and April of 1994 (82% of all those diagnosed during that time pe riod) with 462 age-, gender-, and ethnicity-frequency-matched controls (63% of those eligible from random digit dialing). In addition, limited informa tion was obtained from 101 controls during a brief telephone interview cond ucted with controls who declined participation in the lengthy in-person int erview. Controls who participated in the full inter- view were much more li kely than controls who only completed the telephone interview to report hea d injury [odds ratios (OR) and 95% confidence intervals (CI) were 2.3 (1.0- 4.9) and 3.0 (1.6-5.8) for women and men, respectively]. The OR for any hea d injury in cases versus controls who completed the full interview was 0.9. However, OR for any head injury in cases versus both control groups was 1. 3, 95% CI (1.0-1.7), and the OR for head injury for which the subject sough t medical attention was 1.1, 95% CI (0.8-1.4). Among subjects completing th e full interview, cases who responded by self-report were less likely than controls to report prior non-dental head and neck X-rays (OR = 0.7; 95% CI: 0.5-1.0). However, stratification by respondents' history of head injury i ndicated no difference in history of head and neck X-ray among those withou t prior head injury; OR 0.9; 95% CI (0.6-1.2). Cases and controls shared a very similar history of dental procedures and frequency of dental visits. T hese results suggest that head injury requiring medical attention, dental v isits, or non-dental diagnostic X-rays to the head and neck are not importa nt contributors to the risk of adult glioma and reveal some of the methodol ogical obstacles encountered in forming convincing conclusions about these risk factors for brain tumors, Copyright (C) 2000 S, Karger AG, Basel.