The potential of hybrid SPECT/CT fusion imaging to improve diagnostic accuracy in the scintigraphic quantitative functional assessment of suspected unilateral mandibular hyperactivity

Background Mandibular asymmetry is commonly caused by disproportionate mandibular growth due to unilateral condylar hyperactivity. The current standard for mandibular condyle bone scintigraphy uses single photon emission computed tomography (SPECT) imaging after intravenous administration of technetium-99m-labeled diphosphates. To our knowledge, the use of hybrid SPECT integrated with multidetector computed tomography (SPECT/CT) imaging in the scintigraphic quantitative functional assessment of mandibular condyle growth has not yet been described. Case report A 22-year-old male with mandibular asymmetry due to suspected unilateral condylar hyperactivity underwent SPECT/CT imaging of the skull and facial bones after intravenous administration of technetium-99m methylene diphosphonate. Using CT to guide anatomical contouring, precise regions of interest were drawn over the mandibular condyles and clivus in adjacent SPECT/CT transaxial slices to calculate the mean radiotracer count ratios. For comparison of quantitative results, conventional SPECT images were obtained from the SPECT/CT data and processed according to conventional methods. Planar images were also obtained for visual assessment of mandibular condyle activity. All three methods, SPECT/CT, conventional SPECT, and planar imaging, found unilateral condylar hyperactivity of the left mandibular condyle. The condyles and clivus were easily and confidently identified on SPECT/CT images. Discussion We speculate that SPECT/CT imaging will improve the diagnostic accuracy of unilateral condylar hyperactivity. More studies are necessary to further define its role, obtain baseline reference values, and establish analysis protocols.