Visualization of the drainage veins with contrast-enhanced sonography was useful in diagnosis of small focal nodular hyperplasia.

ocal nodular hyperplasia (FNH) is a benign localized lesion in the liver first reported by Edmondson1 in 1956. Histologically, FNH is defined as a type of tumorlike lesion. Histopathologically, it is sometimes difficult to differentiate FNH from adenoma. Macroscopically, FNH is a nodule without a capsule showing a central stellate fibrous scar spreading from the center of the nodule radially toward the periphery.2 These features have been regarded as the determining factors for imaging diagnosis. In dynamic computed tomography (CT) studies, the FNH is isoattenuating before contrast, showing homogenous hyperattenuation in the early arterial phase and isoenhancement during the portal venous phase. Diagnosis is facilitated by the presence of a central scar, but this feature can only be observed in approximately 50% of cases.3 Although the vascular structure of FNH is said to be characterized by a typical spoke-wheel pattern and a stellate fibrous scar,4 these features are not readily visualized in small FNH lesions. In such cases, it is necessary to differentiate from other hypervascular malignant tumors such as hepatocellular carcinoma (HCC) and metastatic lesions.5 The recent advent of multi–detector row CT, 3-dimensional CT, and single-level dynamic CT during hepatic arteriography has allowed detailed visualization of the hemodynamics of FNH. According to these evaluations, the drainage veins of FNH are mainly the hepatic veins, although they sometimes drain directly into the sinusoids surrounding the tumor.6 However, angiography is invasive, and 3-dimensional volume imaging does not allow real-time presentation. In this case, contrast-enhanced sonography using Levovist (SH U 508A; Schering AG, Berlin, Germany) enhanced the FNH in real time in the early arterial phase and clearly depicted subsequent drainage into the hepatic veins. Received November 23, 2005, from the Department of Diagnostic Ultrasound, Medical Imaging Center, Hyogo College of Medicine, Hyogo, Japan (H.I.); and Departments of Gastroenterology (S.S., F.M., K.Y., M.Ya., T.M., M.Yo., T.H.) and Radiology (N.I., D.K., K.A.), Tokyo Medical University, Tokyo, Japan. Revision requested December 28, 2005. Revised manuscript accepted for publication February 21, 2006. We thank J. Patrick Barron, BA (International Medical Communications Center, Tokyo Medical University), for reviewing the manuscript and Masamichi Kojiro, MD, PhD, (Department of Pathology, Kurume University School of Medicine, Kurume, Japan), for providing advice on histopathologic assessment. Address correspondence to Fuminori Moriyasu, MD, PhD, Department of Gastroenterology, Tokyo Medical University, 6-7-1 Nishishinjuku, Shinjuku-ku, Tokyo 160-0023, Japan. E-mail: moriyasu@tokyo-med.ac.jp Abbreviations CT, computed tomography; FNH, focal nodular hyperplasia; HCC, hepatocellular carcinoma; MRI, magnetic resonance imaging