Whole-Body ⁶⁸Ga-FAPI PET/CT in Cavernous Sinus Syndrome: A Prospective Comparison With ¹⁸F-FDG PET/CT

The goal of this observational study is to evaluate the diagnostic utility of whole-body ⁶⁸Ga-FAPI PET/CT in adults with cavernous sinus syndrome (CSS) in whom magnetic resonance imaging (MRI) failed to establish the underlying cause. The study also compares the performance of ⁶⁸Ga-FAPI PET/CT with paired ¹⁸F-FDG PET/CT. The main questions it aims to answer are: Can whole-body ⁶⁸Ga-FAPI PET/CT detect and characterize cavernous sinus lesions and disease extent in patients with MRI-indeterminate CSS? Does ⁶⁸Ga-FAPI PET/CT provide superior lesion conspicuity and help identify safer biopsy sites compared with ¹⁸F-FDG PET/CT? Researchers will compare whole-body ⁶⁸Ga-FAPI PET/CT with paired ¹⁸F-FDG PET/CT to evaluate lesion detection, quantitative imaging parameters, disease extent, and their impact on identifying appropriate biopsy targets.

Inclusion Criteria: * Adults aged 18 years or older. * Clinical diagnosis of cavernous sinus syndrome (CSS), defined as involvement of two or more cranial nerves (III, IV, V1, V2, or VI) on the same side, or involvement of a single cranial nerve in the presence of a radiologically confirmed cavernous sinus lesion. * Contrast-enhanced MRI demonstrating cavernous sinus pathology but failing to establish a definitive etiological diagnosis. * Ability and willingness to provide written informed consent. * Not receiving definitive etiology-directed therapy before completion of both PET/CT examinations. Exclusion Criteria: * Pregnant or lactating women. * Unwilling or unable to provide written informed consent. * Uncontrolled hyperglycemia precluding performance of ¹⁸F-FDG PET/CT.