Fig. 1

Isthmic spondylolysis: progressive lesion versus terminal stage of chronic nonunited lesion. a Sagittal SPECT/CT image in a 16-year-old female gymnast complaining of lumbar back pain showed intense increased uptake at the right L3 pars defect. Uptake at bilateral L3 pars fractures more prominent on the right is seen in axial SPECT image (b) suggesting progressive lesions more acute on the right; axial CT images at two slightly different levels of L3 vertebra (c, d) show bilateral fracture line defects. e Sagittal SPECT/CT image and axial SPECT image (f) in a 19-year-old female with remote history of cheerleading, presenting with low back pain showed no uptake on the chronic nonunited right L5 pars defect; axial CT images at two slightly different levels of L5 vertebra (g, h) showed fracture line and sclerosis on the right and sclerosis, overgrowth of the contralateral (left) posterior elements and lamina fracture due to stress and bony remodeling in an unstable posterior neural arch