GI Radiography

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Imaging Diagnosis :

Study reveals an isodense mass lesion, with homogenous enhancement on contrast administration.
A diagnosis of hepatocellular adenoma was made, confirmed on MRI.

Discussion:

Helical CT, especially with multiphasic scanning, allows more accurate detection and characterization of focal hepatic lesions. Nonenhanced and delayed contrast-enhanced images can also provide important diagnostic clues in some cases, such as cavernous hemangiomas, which tend to remain isoattenuating with blood vessels, or fibrotic tumors, which tend to demonstrate delayed persistent enhancement. On the basis of helical, multiphasic CT observations and pathophysiology, a group of primary and metastatic hepatic tumors have been classified as hypervascular. The primary hepatic tumors that are often hypervascular include conventional and fibrolamellar HCC, and the benign lesions include hepatic (hepatocellular) adenoma and FNH. Because management of these various tumors is radically different, confident preoperative diagnosis is essential.
Because adenomas consist almost entirely of uniform hepatocytes and a variable number of Kupffer cells, it is not surprising that most adenomas are nearly isoattenuating to normal liver on nonenhanced, PVP, and delayed images. Adenomas enhance completely or nearly homogeneously, except for areas of necrosis, hemorrhage, or focal fatty degeneration.

Because conventional HCC also may contain lipid or fat and may resemble adenoma at MR imaging, it can be difficult to make this distinction with imaging alone. Other criteria, such as interval growth or elevated serum -fetoprotein levels, favor a diagnosis of HCC. An adenoma can undergo malignant change to HCC even after years of a stable appearance.

Adenoma and FNH have several features in common, which include their tendency to occur in young women, and may share certain CT features. FNH does not undergo malignant degeneration, nor is it likely to bleed. FNH may demonstrate small central and septal arteries, along with early draining veins. In distinguishing between FNH and adenoma, MR imaging may be useful. MR imaging is even more sensitive than CT in depicting the characteristic central scar of FNH.

Summary:

Multiphasic, helical CT can demonstrate findings characteristic of hepatic adenoma. These include the presence of a single mass or multiple masses that may contain areas of fat or hemorrhage but that are otherwise nearly isoattenuating to normal liver on nonenhanced, PVP, and delayed scans. The lesions are moderately hyperattenuating to liver on the HAP images and enhance nearly homogeneously. They are sharply marginated and nonlobulated. Other features such as tumor capsule, early draining veins, and calcification are less common and overlap findings encountered in other hepatic masses. Atypical features such as heterogeneous enhancement may require additional imaging, such as MR imaging, or may require biopsy or even surgical resection in some cases to exclude a malignant neoplasm.

Reference

Tomoaki Ichikawa, Michael P. Federle, Luigi Grazioli, and Michael Nalesnik
Hepatocellular Adenoma: Multiphasic CT and Histopathologic Findings in 25 Patients.
Radiology 2000; 214: 861-868
http://radiology.rsnajnls.org/cgi/content/full/214/3/861

Dr. Sandeep Nyayanirgune, Mumbai