Frontal sinus dimensions can differ significantly between individuals within a monozygotic twin pair, indicating environmental influence on sinus sizes

Conclusion: The study showed that the size of the frontal sinus is not determined solely by genotype, but that other factors, e. g. environment, seem to affect the size as well. Environmental factors may include, for example diseases, trauma, allergies, acquired conditions, nutrition or medicine use. Objectives: The purpose of the study was to compare sinus dimensions between individuals within a monozygotic twin pair. Methods: Profile radiographs were obtained from 42 pairs of monozygotic twins, 18 male and 24 female pairs (aged 18-23 years) with no known skeletal deviations in the cranium or general diseases. For each individual the size of the frontal sinus was analyzed on a profile radiograph and compared with the sinus size of the corresponding twin. The variation between twins was estimated using a random effects model for each gender. Results: The sinus sizes varied considerably between twins. The standard deviation between female pairs was 2.98 mm and between male pairs 5.36 mm. The variations in sinus sizes between females and males within twin pairs were not significantly different (p = 0.86 for height and p = 0.83 for width, F test). Still, within one female twin pair and within two male twin pairs, sinus sizes varied significantly between the two individuals.