Background: We have previously found by lateral cephalometry an association between nasopharyngeal anatomy and the risk of acute otitis media (AOM). We evaluate here the association of nasopharyngeal dimensions in magnetic resonance imaging (MRI) with the occurrence of AOM in otherwise healthy children.

Methods: Sixty-one healthy children (mean age 5.7 years, range 3.9–6.9) were recruited from child care centres. The parents filled in a questionnaire on the child's history of ear infections and adenoidectomy. MRI was performed with a 4 mm slice thickness during an upper respiratory infection. Five dimensions and two angles expressing the structure of the bony nasopharynx were measured in sagittal images.

Results: The dimension from the caudal edge of the septum to the midpoint of the sella, reflecting the height of the nasopharynx, was on average 2.2 mm smaller in the children who had had AOM attacks during the last 12 months than those without attacks (95% confidence interval (CI) 0.9 to 3.4, p=0.001) and the nasal base angle was on average 2.1 degrees smaller (95% CI 0.7 to 3.5, p=0.004). These differences remained significant after adjustment for age, sex and previous adenoidectomy in the logistic modelling. A history of adenoidectomy did not have any effect on the dimensions.

Conclusions: The nasopharynx was smaller in the children with AOM attacks during the last year. The value of this finding for predicting susceptibility to recurrent AOM and directing preventive procedures should be evaluated.