Planar versus SPET imaging in the assessment of condylar growth

The aim of this study was to compare two methods of quantifying 99Tc(m)-methylene diphosphonate uptake in the mandibular condyle. The study groups consisted of 23 patients with mandibular asymmetry and 16 normal volunteers aged 10-30 years. The accuracy and reproducibility of SPET using condyle-to-clivus ratios was compared with planar analysis using condyle-to-L4 (fourth lumbar vertebra) ratios. Quantitative analysis was correlated with semi-quantitative grading by three observers. Normal ranges for condyle-to-L4 and condyle-to-clivus ratios in individuals aged 11 years or over were determined. These ratios are useful in the serial monitoring of patients with condylar hyperplasia to establish when condylar growth has ceased and hence the type of surgery performed. Visual interpretation of condylar activity should use a combination of planar and SPET images and be performed in conjunction with quantitative analysis. Semi-quantitative grading on SPET images detected more subtle differences in condylar activity than planar images (using quantitative analysis as a standard).