Common Findings in Liver Imaging Dennis Morrisroe

Liver Anatomy The anatomic divisions of the liver showing the vasculature and biliary system. CT of the normal liver showing general anatomy.

Liver Anatomy A more inferior CT of the normal liver with adjacent structures. MRI of the normal liver with labeled adjacent structures.

Modalities Plain Radiography Ultrasound CT MRI Nuclear Medicine

PLAIN RADIOGRAPHY Limited value for assessing the liver Can demonstrate gross hepatomegaly and hepatic calcification. True borders of the normal liver can only be identified if directly outlined by fat or by free intraperitoneal air. The lungs and diaphragm delineate the apparent superior liver border but a subphrenic collection or a subpulmonary effusion may be misinterpreted as part of the liver itself. As the anterior and inferior border of the liver often extends inferior to the gas-containing lumina of the stomach, duodenum and hepatic flexure of the colon, these gas-filled structures are unreliable guides to the inferior border.

PLAIN RADIOGRAPHY Plain abdominal radiograph demonstrating the lower margin of the liver, marked with H.

Ultrasound First choice imaging modality for RUQ pains, abnormal LFTs, or suspected liver masses. Relatively inexpensive, widely available, and moderately sensitive to localized lesions. Limited utility in the presence of diffuse diseases such as cirrhosis or fatty infiltration, or when air is present. The liver is typically homogeneous in appearance. In general, fluid is anechoic so intrahepatic vessels including portal veins and hepatic veins are visible. The biliary ducts are thin tubes, the walls of which are 1.5 mm or less. The ducts increase in caliber distally from the liver.

Ultrasound Transverse US liver, showing homogeneous parenchyma, the hyperechoic diaphragm the linear portal vein, and the parallel biliary duct (arrow). Hepatic vein branches may be identified by their radiating pattern as they enter the IVC. Normal liver doppler.

CT CT is often employed after US to image focal disease. It is easy to compare in serial studies. Air and bone do not interfere with CT examinations as with US. CT angiography is a noninvasive means of imaging hepatic vasculature. For diffuse hepatocellular disease, CT is probably the first study used, however not as sensitive to liver lesions as MRI. CT is the only commonly accepted means for analyzing abdominal trauma, particularly of the liver. CT is reasonably accurate in the detection of trauma-related abnormalities of the liver, biliary system, and pancreas.

MRI MR imaging may be the most sensitive modality for detecting and characterizing diffuse diseases of the liver, including cirrhosis and hemochromatosis, especially when combined with contrast agents. Newer MR pulse sequences, contrast agents, and fast scanning techniques arguably make MR imaging the optimal means for both detection and characterization of focal liver lesions of all types Often used to characterize focal lesions discovered during survey techniques like US or CT. Angiography may be used to study collateral formation in cirrhosis.

Nuclear Medicine It is most often used to further evaluate masses or tumors. NM has only infrequent applications in diffuse disease Better utility in focal disease such as malignancy or hemangioma.

Diffuse Hepatic Diseases Cirrhosis Fatty Infiltration Hepatitis Hemochromatosis

Cirrhosis T2-weighted MR image demonstrating cirrhosis, consisting of diffuse heterogeneity due to innumerable tiny low signal intensity nodules, regenerative nodules containing fibrous tissue and iron. Also note cholelithiasis (arrow) and splenomegaly

Fatty change Noncontrast CT: right lobe of the liver (RL) is darker than the left lobe (LL) due to fatty infiltration of the right lobe. Caudate lobe (CL) is spared. Normal vascular structures are seen in the right lobe, even without contrast enhancement, because they are surrounded by fat. CT with geographic fatty infiltration of the liver showing well-marginated, focal, low-density portion of the liver posteriorly (arrow).

Hepatitis In chronic hepatitis, the texture of the liver is coarsened as a result of the fibrotic change in the periportal space, and this may decrease the visibility of the portal vein radicles. Findings on CT include hepatomegaly and decreased density Often no important findings except hepatomegaly occur on CT in hepatitis.

Hemochromatosis MRI T1 and T2 weighted axial images through the upper abdomen demonstrating abnormally low and homogeneous signal in the liver Up to 30% of people with this type of hemochromatosis will develop HCC if left untreated

Hemochromatosis T2-weighted MR imaging showing almost completely "black" liver, due to the deposition of intrahepatic iron. CT in iron overload showing dense liver in relationship to the lower density intrahepatic portal vessels.

Liver Masses Simple Cysts Hemangioma Hepatocellular Carcinoma Metastases

Cysts Simple hepatic cysts are the most common cystic lesions of the liver. Probably congenital, with an epithelial lining They are usually small and asymptomatic, whereas large cysts may produce symptoms. Intrahepatic cysts are seen on CT scans as a low-attenuation space-filling lesion. The attenuation coefficient is usually similar to water and always lower than blood. They do not fill with administration of IV contrast dye.

Cysts Hepatic cysts. Low-density areas were found within the liver on this computed tomography (CT) scan done for other purposes. Hepatic US showing hypoechoic cystic lesions.

Hemangioma The most common cause of a hyperechoic liver mass on U/S. Hemangioma is a benign, usually asymptomatic proliferation of vascular tissue, lined with endothelium, which has slow hepatic arterial blood flow. Seen in 7% of adults. Two types: capillary or cavernous. The former is more common.     Can resemble metastases or hepatoma.   Large hemangioma may appear heterogeneous. There may be thrombosis, or a central stellate scar with a giant hemangioma.  

Hemangioma Non-contrast CT: Focal, well-circumscribed, low attenuation lesions Contrast CT: Focal enhancement. 80% of hemangiomas have centripetal opacification pattern on delayed CT. Fills from the periphery in. U/S: subtly hypoechoic (arrows) relative to normal liver parenchyma and lacks an echogenic border .

Hemangioma T1-weighted MRI: Hypointense to liver (arrows). If gadolinium is used, peripheral enhancement is seen initially with central enhancement within 15-30 mins. T2-weighted MRI: Hyperintense to the liver, similar appearance to a cyst. Tagged red blood cell NM scan showing the presence of a region of increased activity within the liver (arrow). Posterior view.

Hepatocellular carcinoma CT: heterogeneously enhancing necrotic mass that may be encapsulated. Vascular invasion can be seen HCC may also be identified using ultrasound. MRI should be performed in patients with severe cirrhosis when CT or ultrasound is equivocal, because MRI more easily detects and characterizes HCC against a background of abnormal parenchyma. Gross specimen of HCC nodule in a cirrhotic liver.

Hepatocellular carcinoma On CT, lesions are most commonly of low density and may enhance in the arterial phase after contrast material administration CT scan of a multi-focal hepatocellular carcinoma in chronic hepatitis B. CT of right lobe hepatocellular carcinoma.

Cancer-Mets PET scan, demonstrating the site of increased metabolic activity, representing the metastatic lesion in the lateral aspect of the liver. Other site is a bowel loop. Most metastases are multiple, diffusely distributed, variable in size, and solid. They may be necrotic and appear more cystic.

Abscess Caused by bacteria (pyogenic) in 80%, amoebic 10% and fungal 10% CT scan (sensitivity 95-100%) Well-demarcated areas are hypodense to hepatic parenchyma. Peripheral enhancement is seen when IV contrast is administered. Gas can be seen in 20-50% of lesions. CT scan is superior in its ability to detect lesions less than 1 cm. Ultrasound (sensitivity 80-90%) Hypoechoic masses with irregularly shaped borders. Internal septations or cavity debris may be detected. Ultrasound allows for close evaluation of the biliary tree and simultaneous aspiration of the cavity. MR imaging demonstrates signs of an irregular, fluid-containing lesion, i.e., low signal intensity on Tl-weighted examinations and high signal intensity on T2-weighted examinations. Edema may be visible surrounding the lesion on T2-weighted images.

Abscess Heterogeneous liver lesion with central necrosis and a peripheral rim of edema CT in pyogenic abscess showing the presence of gas within the lesion (arrow). CT in amoebic abscess showing the presence of an irregular peripherally enhancing lesion.

Trauma On contrast-enhanced CT, areas of parenchymal injury are often lower in density than normal liver. Parenchymal injuries can be categorized by CT as: contusions, subcapsular and parenchymal hematomas, linear or stellate lacerations, and hepatic fractures. Lacerations are the most common form of hepatic injury identified on CT, while contusions and subcapsular hematomas are the least common. CT findings which indicate increased morbidity and the need for more aggressive management include laceration of a major hepatic vein, complex perihilar injuries, progression of a hepatic injury on follow-up studies or persistent hemoperitoneum within one week

Trauma CT A small area of low density (arrow) is seen in the lateral portion of the right lobe, and blood surrounds the liver. ↑ ↑ ↑ ↑ ↑ Another patient shows a much larger area of laceration in the posterior aspect of the right lobe. A central area of increased density (white) (arrow) indicates acute hemorrhage. Lacerations (large arrow) with hemoperitoneum (small arrows

References Atlas of Internal Medicine. Braunwald, E. 2007. Basic Radiology. M. Y.M. Chen, T. L. Pope, Jr., D. J. Ott. 2004. McGraw-Hill Medical. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging, 4th ed. 2001 Churchill Livingstone, Inc. Mettler: Essentials of Radiology, 2nd ed. 2005 Saunders Medscape.com Emedicine.com