Dual-tracer PET/CT for the differential diagnosis of small liver nodules (1-2 cm) in cirrhosis: Early HCC or dysplastic nodule?

Objectives Contrast CT was less accurate in the differentiation of small liver nodules (1-2 cm), particularly in severe cirrhosis. We evaluated the accuracy of dual-tracer (¹¹C-acetate: ACT and ¹⁸F-FDG: FDG) PET/CT for the differentiation between small HCC and dysplastic nodules in cirrhotic liver as compared to contrast CT.

Methods Patients with cirrhosis and HCC 1-2 cm confirmed by postoperative pathology after liver transplant or hepatectomy were included if they had both preoperative dual-tracer PET/CT and contrast CT within 1 month. For the diagnosis of HCC, dual-tracer PET/CT was reviewed qualitatively by 3 nuclear medicine physicians in consensus, supported by lesion-to-liver SUV>1.20 (either tracer). Diagnosis by CT was made by 2 radiologists based on the triple-phase pattern of arterial contrast enhancement and washout during portal venous or delayed phase. Each lesion was compared with pathology in terms of diagnosis, size and location. Statistics were analysed by Chi-square and student t tests.

Results 20 patients (M: 15, F: 5, mean: 54±9.2y) with 23 small HCC lesions and 12 dysplastic nodules were identified by postoperative pathology. The mean size of small HCC was 1.6±0.35 cm, dysplastic nodules 1.5±0.34 cm (p>0.05). ACT PET identified 20/23 (87.0%) small HCC lesions while FDG detected 4/23 (17.4%) with dual-tracer sensitivity of 91.3% (21/23). ACT and dual-tracer PET were significantly more sensitive for the diagnosis of early HCC than contrast CT (10/23: 43.5%), with both p<0.05. Of the 23 small HCC lesions, 15 (65.2%) were well and 8 (34.8%) were moderately differentiated. Both FDG and ACT were true negative for all dysplastic nodules (specificity: 100%); while contrast CT misdiagnosed 4 dysplastic nodules as early HCC (specificity: 66.7%).

Conclusions Dual-tracer PET/CT was superior to contrast CT for differentiating small HCC from dysplastic nodules (1-2 cm) in cirrhotic livers. ACT was the PET tracer essential for early HCC detection