Molecular imaging in adult spondylodiscitis: current evidence, clinical applications, and future perspectives

Adult spondylodiscitis is an infection of the intervertebral disc and adjacent vertebral bodies that may progress to paravertebral extension, epidural involvement, spinal instability, sepsis, and neurological compromise. Because clinical symptoms and laboratory markers are often nonspecific, imaging is central to diagnosis, assessment of disease extent, biopsy planning, and selective evaluation of treatment response. Magnetic resonance imaging (MRI) remains the first-line anatomical technique for early marrow, disc, epidural, and paraspinal disease, while computed tomography (CT) is valuable for osseous destruction, instability, and biopsy guidance. Molecular imaging complements these modalities by depicting biological activity rather than structure alone. Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography ([18F]FDG PET/CT) is the most established molecular technique, offering high diagnostic performance, whole-body evaluation for multifocal or metastatic infection, and support for management when MRI is contraindicated, equivocal, or difficult to interpret after surgery. Its main limitations are limited pathogen specificity, uptake in sterile inflammatory or reparative processes, heterogeneous interpretation criteria, and uncertain thresholds for treatment monitoring. Emerging approaches, including hybrid positron emission tomography/magnetic resonance imaging (PET/MRI), fibroblast activation protein inhibitor (FAPI) tracers, pathogen-targeted radiopharmaceuticals, quantitative PET biomarkers, and artificial intelligence (AI), remain investigational and require prospective validation of diagnostic and clinical utility. This review summarizes current evidence, clinical applications, limitations, and future directions for molecular imaging in spondylodiscitis.