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EDUCATION EXHIBIT |
Department of Radiologic Pathology, Armed Forces Institute of Pathology, Washington, DC, Department of Radiology and Nuclear Medicine, Uniformed Services University of the Health Sciences, Bethesda, Md
FNH is an uncommon liver lesion that is being detected with increasing frequency due to advances in CT and MR imaging technology that facilitate rapid imaging of the liver during the arterial and early portal venous phases of contrast enhancement. Even though there is abundant radiology, surgery, and pathology literature on the diagnosis and management of FNH, the imaging and pathologic diagnosis continues to be challenging because FNH has a diverse spectrum of features.
In many cases, the imaging features overlap with those of hepatocellular adenoma, HCC, fibrolamellar carcinoma, and hypervascular metastasis so that imaging-guided biopsy is necessary to establish the diagnosis. Such lesions have been called atypical FNH because they lack the typical CT and MR imaging features: lesion homogeneity, marked arterial enhancement, a central scar, and intermediate or slightly high signal intensity on T2-weighted MR images. However, the pathologic diagnosis of FNH is not always straightforward because many small lesions with atypical imaging features also have atypical pathologic features such as absence of a central scar, presence of a portal vein, adenomatous features, or telangiectatic changes (1).
In the preceding article, Hussain et al (2) elegantly review and illustrate the pathologic spectrum of FNH with an emphasis on the pathologic classification introduced by Nguyen et al (3) that divides FNH into classic and nonclassic forms. They have superbly demonstrated the imaging of classic FNH. However, they do not illustrate the imaging features of nonclassic FNH (telangiectatic FNH, mixed hyperplastic and adenomatous FNH, and FNH with areas of large cell change or cytologic atypia).
Nonclassic FNH is rare in our experience at the Armed Forces Institute of Pathology. To my knowledge, the imaging appearance of only 15 cases of telangiectatic FNH has been reported in the English medical literature, and there are no reports on the imaging appearance of mixed hyperplastic and adenomatous FNH or FNH with large cell change (4–6). In the series of 13 cases of telangiectatic FNH reported by Attal et al (6), the lesions were characterized by having at least two of the following imaging features: multiplicity, lack of a central scar, lesion heterogeneity, high signal intensity on T1-weighted MR images, marked high signal intensity on T2-weighted MR images, or persistent contrast enhancement on delayed CT or MR images. There were no cases of telangiectatic FNH in their series that displayed the typical FNH imaging pattern.
The atypical imaging features of FNH have been well described (7,8). These features include lesion heterogeneity, atypical contrast enhancement patterns (persistent enhancement in the portal venous phase, low attenuation in the portal venous phase, and delayed capsulelike enhancement), and high signal intensity on T1-weighted MR images. Our knowledge of the pathologic basis for these features is limited. Although it is possible that many cases with atypical imaging features correlate pathologically to nonclassic FNH, this has not been established.
In conclusion, the article by Hussain et al (2) in this issue of RadioGraphics brings us up to date on the current knowledge of FNH and is stimulus for further radiologic-pathologic investigation of nonclassic FNH. As we begin to understand the varied radiologic and pathologic appearances of FNH, we must appreciate that our current knowledge of the natural history of nonclassic FNH is absent. We need prospective studies to validate the pathologic criteria, establish the imaging criteria, and document the biologic behavior of unresected nonclassic FNH in order to establish appropriate clinical management for these lesions.
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