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Gastrointestinal Imaging

E3112. Radiologic-pathologic correlation of hepatocellular adenoma to understand the MR imaging

Cannella R1,2,  Vernuccio F1,3,  Minervini M4,  Vilgrain V3,  Furlan A.2 1. Section of Radiology -Di.Bi.Med., University Hospital “Paolo Giaccone”, Palermo, Italy; 2. Department of Radiology, Abdominal Imaging Division, University of Pittsburgh, Pittsburgh, Pennsylvania; 3. Department of Radiology AP-HP, Hôpital Beaujon, University Paris-Diderot, Clichy, France; 4. Department of Pathology, Universiy of Pittsburgh, Pittsburgh, Pennsylvania

Address correspondence to R. Cannella (rob.cannella89@gmail.com)

Background Information: Hepatocellular adenoma (HCA) is a rare benign liver tumor that occurs most frequently in young woman. These lesions are not a single and uniform entity and they can be manly divided in four subtypes according to a genotype-molecular classification: 1) HNF1a-mutated HCA (35-40% of all lesions); 2) Inflammatory HCA (40-50%); 3) ß-catenin activated HCA (10%); 4) Unclassified HCA (10%). The main complications of HCA are hemorrhage and malignant transformation. A timely and accurate diagnosis is important because the risk of malignant transformations is different among the four subtypes, being the lowest in HNF1a-mutated HCA and the highest in ß-catenin activated HCA. MR imaging (MRI) is the preferred imaging test for the non-invasive diagnosis of HCA. The MRI appearance changes according to the lesion group and strongly correlates with the histologic phenotype. Therefore, a radiology-pathology correlation of HCA will help the radiologist to understand the imaging appearance and to formulate an accurate diagnosis.

Educational Goals/Teaching Points: The goals of this educational exhibit are: 1) To review the current molecular classification and histologic features of HCA; 2) to correlate the appearance of HCA on MRI with the histologic phenotype; 3) to review and illustrate tumor complications and uncommon growth patterns.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques: The educational exhibit will provide a concise review of the current molecular classification of HCA and of the corresponding histologic phenotypes. A summary of the available literature on the imaging appearance of HCA on Gd-BOPTA and Gd-EOB-DTPA MRI will be provided. Using explanatory pathologic-proven cases diagnosed at our institution we will correlate the histologic phenotype with the typical imaging appearance. HNF1a-mutated HCA is characterized by marked steatosis that appears on MRI as a significant homogeneous loss of signal on the T1WI acquired out-of-phase or on fat-saturated imaging (78-80%). The sinusoidal dilatation typically seen in inflammatory HCA manifests as mild hyperintensity on T2WI (81-83%), frequently with a peripheral distribution, a pattern described as “atoll sign” (38-43%). Moreover, inflammatory HCA commonly shows moderate-to-marked arterial hyperenhancement (48-86%) given the presence of dystrophic vessels and persistent enhancement on delayed phase. ß-catenin activated HCA is radiologically difficult to distinguish from hepatocellular carcinoma showing arterial hyperenhancement and portal venous washout. Unclassified HCA has a heterogeneous imaging presentation without typical MRI or histological features. The exhibit will also provide illustrative radiology- pathology examples of HCA with uncommon growth patterns (i.e. adenomatosis, exophytic, pedunculated) and of complicated HCA (i.e. hemorrhage and malignant transformation).

Conclusion: HCAs are a heterogeneous class of benign liver tumors with different histologic phenotypes and corresponding imaging appearances. Knowledge of the histologic features of HCA will help the radiologist to understand the MRI presentation and to formulate a confident and timely diagnosis.