A Proof-of-Concept Pilot Study of Contrast-Enhanced Ultrasound as a Potential Alternative to Contrast-Enhanced Magnetic Resonance Imaging in the Surveillance of Hepatocellular Adenoma and Focal Nodular Hyperplasia

<b>Background</b>: Focal nodular hyperplasia (FNH) and hepatocellular adenoma (HA) are benign hepatic tumors that predominantly affect women of reproductive age and are associated with hormonal and metabolic factors. While FNH is a non-progressive lesion without malignant potential, HA carries a relevant risk of hemorrhage and malignant transformation. Differentiation between these entities remains challenging due to overlapping imaging features. Although contrast-enhanced magnetic resonance imaging (MRI) is considered the diagnostic reference standard, its cost, limited availability, and contraindications restrict routine long-term use. Therefore, contrast-enhanced ultrasound (CEUS) has emerged as an alternative modality for follow-up. This study evaluated the effectiveness of CEUS in long-term monitoring of FNH and HA compared with MRI. <b>Methods</b>: Patients with imaging-confirmed FNH or HA underwent paired CEUS and MRI examinations within 48 h at baseline and follow-up. Lesion size was assessed using maximal and minimal diameters, and longitudinal changes were classified according to RECIST-like criteria. Paired non-parametric statistical tests were applied. <b>Results</b>: 41 benign liver lesions (28 FNH and 13 HA) were analyzed across 92 paired examinations. Baseline lesion measurements were comparable between CEUS and MRI. A statistically significant difference was observed in the assessment of the largest lesion diameter, while no significant differences were detected for the shortest diameter. Longitudinal evaluation showed no significant differences between modalities in detecting lesion size changes. Response classification was concordant in 42 of 51 follow-up assessments, with stable disease as the most frequent outcome. <b>Conclusions</b>: After definitive diagnosis, CEUS may serve as a reliable standalone modality for routine long-term surveillance of FNH and HA in clinically stable patients. Its performance in lesion measurement and response assessment is comparable to MRI, while offering advantages in cost, accessibility, and patient tolerability. MRI may be reserved for cases with suspicious changes on CEUS.