Diagnostic accuracy of CEUS in the differential diagnosis of small (≤ 20  mm) and subcentimetric (≤ 10  mm) focal liver lesions in comparison with histology. Results of the DEGUM multicenter trial.

Objective: To evaluate the diagnostic accuracy of contrast-enhanced ultrasound (CEUS) in the differential diagnosis of small and subcentimetric liver tumors in clinical practice.

Methods: 1349 patients with a hepatic tumor lacking a definite diagnosis based on B-mode ultrasound and power Doppler ultrasound were examined at 14 hospitals by CEUS using a standardized protocol (pulse/phase inversion imaging, mechanical index < 0.4). Differential diagnosis was based on the vascularity pattern and contrast enhancement pattern during the arterial, portal, and late phase according to the EFSUMB guidelines. 335 patients with focal liver lesions (FLL) ≤ 20  mm were analyzed. The tumor status established after CEUS was compared to histology (73.2 %) or in some cases to CT or MRI.

Results: A definitive diagnosis based on the gold standard was possible in 329 FLLs, while 6 FLLs remained unclear even in the combined gold standard (histology and/or CT and/or MRI). The final diagnoses of ≤ 20  mm FLL with histological confirmation (n = 241) included 87 benign and 154 malignant entities. The overall diagnostic accuracy of CEUS in FLL ≤ 20  mm with histological confirmation was 83.8 %. CEUS correctly identified 144 /154 malignant FLLs (sensitivity 93.5 %) and 58 /87 benign FLLs (specificity 66.7 %). 24 /241 FLLs remained unclear after CEUS (9.9 %). CEUS misclassified 15 /241 FLLs (6.2 %; 12 benign and 3 malignant FLLs). The positive predictive value of CEUS for a malignant FLL was 92.3 % and the negative predictive value was 95.1 %. Out of 241 small FLLs with histological confirmation, 62  FLLs were ≤ 10  mm (diagnostic accuracy of CEUS 80.6 %) and 179 FLLs were > 10  mm and ≤ 20  mm (diagnostic accuracy of CEUS 84.9 %).

Conclusions: CEUS has a high diagnostic accuracy for the differential diagnosis of small and subcentimetric FLLs in clinical practice.