Magnetic Resonance Materials in Physics, Biology and Medicine 10 (2000) 200 – 204 Enhancement characteristics of hepatic focal nodular hyperplasia and its scar by dynamic magnetic resonance imaging Luis Martı ´-Bonmatı ´ *, Carlos Casillas, Rosa Dosda ´ Department of Radiology, Doctor Peset Uniersity Hospital, Ada Gaspar Aguilar 90, E-46017 Valencia, Spain Received 29 October 1999; accepted 14 January 2000 Abstract Rationale and objecties : To determine the relationship between the lesion and the scar enhancement characteristic in a series of hepatic Focal Nodular Hyperplasia (FNH) lesions studied with dynamic MR imaging. Methods : Nine patients with FNH were studied. The slice showing the largest scar was selected for the dynamic single slice T1-weighted Gradient-echo sequence before and after contrast administration (15 images, one every 20 s). Analysis was performed with ROI measurements in the lesion and the scar. Signal-intensity and enhancement curves were obtained from both structures. Results : Dynamic MRI showed the typical homogeneous early enhancement of the lesion with delayed enhancement of the scar. The scar enhanced early and vigorously in all cases. Two patterns of enhancement curves were defined. In the parallel pattern, both curves started early, quickly reaching a plateau maintained over time (77.8%). In the divergent pattern the curve of the scar was above the curve of the FNH (22.2%), after the maximum slope was reached, with progressive separation of the curves. Conclusion : There is a hypervascular scar enhancement within FNH lesions with either a parallel or divergent course after the maximum early enhancement. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Magnetic resonance (MR); Contrast enhancement — liver; Focal nodular hyperplasia — liver neoplasms; MR www.elsevier.com/locate/magma 1. Introduction Focal nodular hyperplasia (FNH) is a benign hepatic tumor that likely represents a focal hyperplastic re- sponse of the liver to a vascular anomaly. The mass is characterized by a central fibrous scar with surrounding nodules of hyperplastic hepatocytes and small bile duc- tules. The fibrous scar contains thick-wall vessels that provide excellent arterial blood supply [1]. FNH lesions are well-demarcated and non encapsu- lated liver tumors without surrounding edema. These benign lesions are usually homogeneous and have low lesion-to-liver contrast in T1 weighted, proton density weighted and T2 weighted images with a characteristic central scar, more frequently seen in large tumors [1]. This scar is hyperintense to the lesion on T2 weighted images due to edema, although hypointense scars can also be found [2]. Gadopentetate dimeglumine is a MR non-specific extracellular contrast media initially distributed within the intravascular compartment. This agent diffuses rapidly to the extracellular interstitial space. The con- trast agent affects the image characteristics of both the normal liver parenchyma and the different components of the liver tumors. The most common criteria pro- posed for the differentiation of the different liver tu- mors is related to the pattern of enhancement after a rapid bolus injection [3 – 6]. These patterns of tumor enhancement depend mainly on the vascularization and diffusion kinetics of the contrast agent inside the lesion [4]. FNH is usually a hypervascular lesion [7,8], with a short but intense and homogeneous arterial enhance- ment, becoming isointense to the liver in the portal venous and delayed interstitial phases. It has been observed that the scar enhances progressively after the lesion, although with a variable progression [7,8]. In late delayed interstitial images the scar is usually visible as a hyperintense structure, providing a very useful diagnostic sign. However, the relation between lesion * Corresponding author. Tel.: +34-963862520; fax: +34- 963862534. E-mail address: marti – lui@gva.es (L. Martı ´-Bonmatı ´) 1352-8661/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 1 3 5 2 - 8 6 6 1 ( 0 0 ) 0 0 0 8 8 - 0