Contrast-enhanced ultrasound of focal nodular hyperplasia: a matter of size.

OBJECTIVES: To assess the contrast-enhanced ultrasound (CEUS) frequencies of centrifugal enhancement, spoke-wheel sign and central scar in focal nodular hyperplasia (FNH) as a function of lesion size.

METHODS: Ninety-four FNHs were retrospectively reviewed to assess their largest diameter and enhancement pattern, including centrifugal enhancement from one central artery, spoke-wheel sign, diffuse or centripetal enhancement, central scar and late-phase washout.

RESULTS: Mean FNH-lesion size was 3.7 ± 2.1 cm. Only 43.6 % of FNHs had centrifugal enhancement, with a spoke-wheel pattern (23.4 %) or without (20.2 %), while 56.4 % showed diffuse or centripetal enhancement. Centrifugal enhancement was observed in 73.9 % of FNHs ≤3.1 cm and 14.6 % of FNHs >3.1 cm (P < 10(-4)). Size and frequency of centrifugal enhancement were negatively correlated (r = -0.57, P < 10(-4)). The spoke-wheel pattern was also seen more frequently in smaller (37 %) than in larger FNHs (10.4 %) (P < 10(-3)). Late-phase washout was described in 5.3 % of FNHs and was not size-dependent. Lesions with a central scar were larger than those without, respectively, 5.7 ± 1.7 and 3.6 ± 2.0 cm (P = 0.012).

CONCLUSIONS: Typical centrifugal enhancement yielding a confident FNH diagnosis is seen significantly more frequently when the lesion is ≤3.1 cm.

KEY POINTS: • CEUS yields confident diagnoses of FNHs ≤3.1 cm • The larger the FNH, the lower the diagnostic sensitivity of CEUS • Final diagnosis of FNHs >3.1 cm should be obtained with MRI not CEUS.