Histological characteristics of small hepatocellular carcinomas showing atypical enhancement patterns on gadoxetic acid-enhanced MR imaging.

Purpose: To define the histological characteristics of hepatocellular carcinomas (HCCs) showing atypical dynamic enhancement patterns on gadoxetic acid-enhanced dynamic magnetic resonance imaging (EOB-MRI).

Materials And Methods: We evaluated a total of 130 small (≤ 3 cm) HCCs from 114 patients that were surgically removed after EOB-MRI. Two radiologists blinded to the histological findings retrospectively classified the HCCs into typical or atypical lesions. Gross morphology, nuclear histological grade, presence of vascular invasion, and capsule formation and infiltration were compared between the two groups using Chi-square or Fisher tests.

Results: Atypical dynamic enhancement patterns were seen in 23 HCCs (17.7%). None of the atypical HCC showed vascular invasion (P < 0.001). Atypical HCCs also showed more frequently smaller size (1.6 ± 0.6 cm versus 2.1 ± 0.6 cm, P = 0.001) with 86.9% (n = 20) of which 2 cm or less in diameter (P = 0.001), vaguely nodular appearance (56.5% vs 3.7%, P < 0.001), and nuclear grade I (69.6% versus 6.5%, P < 0.001), while less frequently showed capsule formation (26.1% versus 77.6%, P < 0.001) or capsular infiltration (16.7% versus 77.1%, P = 0.005).

Conclusion: Atypical HCCs on EOB-MRI may be characterized by the absence of vascular invasion, smaller (< 2 cm or less) size, vaguely nodular appearance, and well differentiation, and infrequent capsule formation or capsular infiltration.