129 Review of the role of bone-SPECT/CT in tarsal coalitions Types of tarsal coalitions and imaging Non-osseous calcaneonavicular coalition (CNC) In CNC, the increased bone turnover on planar scintigraphy is located in the lateral aspect of the articulation between hind- and midfoot. The location and pattern on planar bone scintigraphy should usually already be strongly suggestive for a CNC [Figure 4, panel A]. In TCC, the increased bone turnover on planar scintigraphy is expected laterally in the hindfoot. Still, the uptake itself is non-specific and could also be attributed to other diseases, such as a fracture, severe unifocal inflammatory arthritis or to osteoarthritis with considerable reactive inflammation. Bone-SPECT/CT images may improve specificity, in CNC the CT part will often show the anteater nose sign, as well as an irregular surface of the articulating bones, and subchondral cysts. A clear increased bone turnover at the site of the CNC is usually present, absence of increased bone turnover elsewhere in the foot excludes other active pathologies. All the cross-sectional techniques (CT, MRI and bone-SPECT/CT) depict the extent of the TC more precisely than plain radiographs [Figure 4, panel B]. Moreover, MRI is better equipped to depict the adjacent soft tissue structures, and bone-SPECT/CT excelling in fast and accurate characterization of the bony pathology and excluding any synchronous pathology elsewhere in the foot and ankle. Bone-SPECT/CT is often able to ascertain (non-osseous) CNC to be the very likely pain generator because of the focal increased bone turnover and is accurate to exclude any other active bone pathology in the feet or ankles with high confidence. Figure 5. Ninteen-year-old male patient, with midfoot pain on the left and the presence of calcaneonavicular: MRI showed the calcaneonavicular with moderate bone-marrow edema (T2 fat saturation); however, with no clear visualization of the ossified fragment with this modality. 5