134 Part IID – Primary Solid Liver Lesions in Non-Cirrhotic Liver
63Hepatocellular Adenoma II – Large Exophytic with Pathologic Correlation
Hepatocellular adenoma (HCA) contains fat in up to 78 % of cases. The size may vary between a few millimeters and several centimeters. Occasionally, the lesions may be exophytic and contain large vessels.
MR Imaging Findings
At MR imaging, fat-containing HCAs are bright on T1-weighted inphase images and decrease their signal intensity on T1-weighted opposed-phase images due to the presence of a small amount of fat. Some areas within fatty HCAs may appear dark on fat-suppressed T2-weighted images as well as on three-dimensional gadoliniumenhanced gradient-echo images in the delayed phase because the amount of fat may be sufficient to be affected by the fat-suppression pulse. On the delayed images, this finding may mimic washout (Figs. 63.1, 63.2). At gross pathology, fat-containing HCAs have yellowish areas. At histology, the lesions resemble liver tissue and are often surrounded by a pseudocapsule which consists of compressed liver parenchyma (Fig. 63.3).
Literature
1.Baum JK, Holtz F, Bookstein JJ, et al. (1973) Possible association between benign hepatoma and oral contraceptives. Lancet 2:926 – 929
2.Terkivatan T, de Wilt JH, de Man RA, et al. (2001) Indications and longterm outcome of treatment for benign hepatic tumors: a critical appraisal. Arch Surg 136:1033 – 1038
3.Hussain SM, Van den Bos IC, Dwarkasing S, et al. (2006) Hepatocellular adenoma: findings at state-of-the-art magnetic resonance imaging, ultrasound, computed tomography and pathologic analysis. Eur Radiol 16:1873 – 1886
Management
The management of HCAs should be individualized based on their size and mode of presentation. The initial step should be to stop any oral contraceptive use. Patients should be informed about the increased risk of hemorrhage, the potential risk of malignant transformation, and the increased risk of rupture particularly during pregnancy. Patients with lesions smaller than 5 cm and normal al- pha-fetoprotein can be safely observed and followed by MR imaging. HCAs > 5 cm should be considered for surgical or other types of treatment due to the risk of malignancy. Surgery is controversial, particularly in patients with multiple lesions and lesions located at difficult anatomic locations. In patients with multiple adenomas or liver adenomatosis, surgical resection or other local treatment may be technically impossible. Interval growth and/or elevated serum alpha-fetoprotein levels in patients with a known hepatocellular adenoma suggest malignant transformation. HCAs with hemorrhage may be treated with hepatic arterial embolization to control the hemorrhage.
63 Hepatocellular Adenoma II – Large Exophytic with Pathologic Correlation 135
Fig. 63.1. Adenoma, drawings. T2 fatsat: adenoma is slightly hypointense to the liver; T1 in-phase: adenoma is almost isointense to slightly hyperintense to the liver; ART: adenoma shows a moderately intense homogeneous en-
Fig. 63.2. Adenoma with fatty infiltration. A Axial fat-suppressed T2-w TSE image (T2 fatsat): adenoma is isointense to the liver. B Axial in-phase T1-w GRE (T1 in-phase): adenoma is slightly hyperintense to the liver. C Axial arterial phase post-Gd 3D T1-w GRE image (ART): adenoma shows moderately intense and homogeneous enhancement. D Axial delayed phase GRE image (DEL): adenoma becomes slightly hypointense to the liver, likely due to the fatty contents of the lesion. E Axial 2D T1-w GRE image (T1 fatsat): a part of the adenoma that is most fatty has a lower signal (arrow). F Axial op-
hancement of the entire lesion; DEL: adenoma becomes almost isointense to slightly hypointense
posed-phase 2D T1-w GRE image (T1 opposed-phase): some parts of the lesion lose their signal more than other parts, indicating a variable amount of fatty infiltration (arrows). G Coronal delayed phase post-Gd 3D GRE image (DEL) with high spatial resolution clearly shows the adenoma as an exophytic lesion (arrow). H A detailed view of the previous image (DEL) shows the tumor anatomy better (arrow) with a large intratumoral vessel, most likely with accompanying fibrotic tissue
Fig. 63.3. MR-pathology correlation. A Photomicrograph shows a small fatty adenoma surrounded by large vessels (arrows). H&E, × 40. B Photomicrograph from the resected adenoma shown above: note normal appearing hepatocytes with fat, large vessels, and compressed parenchyma. H&E, × 200.
C Photomicrograph shows the findings in more detail. H&E, × 400. D Photograph of the gross specimen: large parts of the tumor contain fat and appear yellowish
136 Part IID – Primary Solid Liver Lesions in Non-Cirrhotic Liver
64 Hepatocellular Adenoma III – Typical Fat-Containing
Fat-containing hepatocellular adenomas (HCAs) are among a variety of other fat-containing tumors of the liver with characteristic histologic features and variable imaging findings. Other common liver lesions that contain fat include focal fatty infiltration (steatosis), focal nodular hyperplasia (FNH), and hepatocellular carcinoma (HCC). Uncommon fat-containing liver lesions include angiomyolipoma, lipoma, liposarcoma, and teratoma. Identification of fat within a liver lesion can be critical in the characterization of the lesion. The imaging characteristics of a lesion such as enhancement pattern combined with the pattern of fatty content and the presence of Kupffer cells are helpful in narrowing the differential diagnosis. Computed tomography or ultrasound may indicate the presence of a within hepatic lesion, and MR imaging is the most specific imaging technique for demonstration of both microscopic and macroscopic fat based on the chemical shift imaging and fat suppressed sequences.
Literature
1.Prasad SR, Wang H, Rosas H, et al. (2005) Fat-containing lesions of the liver: radiologic-pathologic correlation. Radiographics 25:321 – 331
2.Wang YX, Hussain SM, et al. (2001) Superparamagnetic iron oxide contrast media: physicochemical characteristics and applications in MR imaging. Eur Radiol 11:19 – 31
3.Hussain SM, Van den Bos IC, Dwarkasing S, et al. (2006) Hepatocellular adenoma: findings at state-of-the-art magnetic resonance imaging, ultrasound, computed tomography and pathologic analysis. Eur Radiol 16:1873 – 1886
MR Imaging Findings
At MR imaging, minimally fat-containing HCAs are near isointense on the T1and T2-weighted sequences, drop their signal on op- posed-phase images, show homogeneous enhancement in the arterial phase, and fade to isointensity on the delayed phase images. HCAs show uptake of the superparamagnetic iron-oxide (SPIO) based contrast media and reveal the presence of a small amount of Kupffer cells. Such contrast media can be used to distinguish between primary and secondary liver lesions. Specific contrast media such as SPIO cannot replace dynamic gadolinium-enhanced imaging because the enhancement patterns play an essential role in the characterization of liver lesions at MR imaging (Figs. 64.1, 64.2). At histology, fat-containing liver lesions may show striking similarity (Fig. 64.3).
Differential Diagnosis
Focal fatty infiltration is often geographic, shows signal drop on the opposed phased imaging and does not show washout on the gado- linium-enhanced delayed phase images. FNH contains fat in approximately 6 % and HCC in about 10 % of cases and they have tumor morphology and enhancement patterns distinct from HCA at MR imaging.
64 Hepatocellular Adenoma III – Typical Fat-Containing 137
Fig. 64.1. Adenoma, fat containing, drawings. T2 fatsat: adenoma is isointense with a thin bright pseudocapsule; T1 in-phase: adenoma is isointense to the liver; ART: adenoma shows an intense homogeneous enhancement of the
Fig. 64.2. Adenoma, typical, fat containing, MRI findings. A Axial fat-suppressed T2-w TSE image (T2 fatsat): Adenoma is isointense and only visible due to mass effect and a bright pseudocapsule. B Axial in-phase GRE (T1 inphase): Adenoma is isointense to the liver. C Axial arterial phase GRE image (ART): Adenoma shows homogeneous enhancement. D Axial delayed GRE image (DEL): Adenoma becomes slightly hypointense due to fat suppression and not due to washout. Note the enhanced pseudocapsule. E Axial TSE image after SPIO (T2 fatsat post-SPIO): Adenoma shows drop in signal in the
entire lesion; DEL: adenoma becomes slightly hypointense to the liver most likely due to fat suppression and not due to washout of contrast material. Note the enhancement of the pseudocapsule
periphery of the lesion, indicating its hepatic origin (arrow). F Axial op- posed-phase GRE image (T1 opposed-phase): Adenoma drops its signal due to homogeneous fatty infiltration (arrow). G Axial fat-suppressed T2-w black-blood echoplanar image (BBEPI): Adenoma is isointense to the liver (arrow). H Axial BBEPI after SPIO (BBEPI post-SPIO): Adenoma shows drop in signal particularly in the periphery of the lesion due to the presence of the Kupffer cells (arrow)
Fig. 64.3. Adenoma, and other fatty tissues and tumors, histology findings. A Photomicrograph of a focal fatty infiltration of the liver visible as a lesion at imaging. H&E, × 200. B Photomicrograph from a fatty adenoma (note the similarity with the previous image). H&E, × 200. C Photomicrograph of bi-
opsy from a fatty focal nodular hyperplasia (FNH). H&E, × 100. D Photomicrograph of biopsy from a fatty hepatocellular carcinoma (HCC). H&E, × 200