Different Features of (18)F-FAPI, (18)F-FDG PET/CT and MRI in the Evaluation of Extrahepatic Metastases and Local Recurrent Hepatocellular Carcinoma (HCC): A Case Report and Review of the Literature

BACKGROUND: Recurrence and metastasis are important causes of postoperative death in most HCC patients. Conventional imaging modalities such as (18)F-FDG PET/CT and enhanced MRI are still unsatisfactory in evaluating these patients in the clinical setting. PET/CT imaging with a radiolabeled fibroblast activation protein inhibitor (FAPI) has emerged as a new imaging technique for the diagnosis and radiotherapy of malignant tumors. While many studies have focused on the diagnostic accuracy of intrahepatic primary HCC, the evaluation of recurrent and metastatic HCC remains only poorly investigated. CASE PRESENTATION: A 71-year-old man with a five-year history of HCC after radical resection underwent (18)F-FDG PET/CT due to further surgery for tumor recurrence, which revealed two iso-metabolic lesions in the right peritoneum and a hypo-metabolic lesion in the right liver. (18)F-FAPI PET/CT was performed to further complement (18)F-FDG PET/CT in the detection of these suspected metastatic lesions. Importantly, multiple diffuse intense radioactivity was shown in the hepatic capsule, suggesting metastatic lesions, but a wedge-shaped elevated (18)F-FAPI uptake disorder around the FDG-unavid necrotic lesion after radiofrequency ablation (RFA) demonstrated benign stromal fibrosis. CONCLUSION: This case suggested that (18)F-FAPI may have an advantage over (18)F-FDG in detecting peritoneal metastasis even in tiny or early hepatic capsules of HCC, but its false positives due to postoperative stromal fibrosis should be noted. Wedge- or strip-shaped FAPI-avid lesions with sharp edges may be post-treatment stromal fibrosis.