Liver Imaging Study Guide

Audio Overview:

A hemangioma typically appears very bright on a T2W image, approaching the signal intensity of cerebrospinal fluid. This is sometimes referred to as the “light bulb” sign.

Classic features for HCC in a patient with cirrhosis include arterial enhancement, washout appearance on delayed phase, and often capsule appearance on delayed phase.

FNH typically accumulates hepatobiliary contrast agent and remains iso- to hyperintense to the liver on the hepatobiliary phase, while HCAs are typically hypointense on this phase.

According to LI-RADS, hypointensity on the 20-minute hepatobiliary phase is considered an ancillary feature that favors HCC in patients at risk.

Cholangiocarcinoma typically shows little arterial enhancement and progressive delayed enhancement on dynamic contrast-enhanced imaging due to the fibrotic stroma within the tumor.

Portal vein tumor thrombus in a patient at risk for HCC increases the confidence level for diagnosing HCC and is often classified as LR-5V according to LI-RADS.

The “starry-sky” appearance on ultrasound of the liver is characterized by diffuse decreased echogenicity of the parenchyma with conspicuous, hyperechoic walls of the portal venules, often seen in acute hepatitis.

The “hot spot sign” on CT, characterized by intense early enhancement of the medial segment left hepatic lobe, is diagnostic for superior vena cava (SVC) obstruction.

Intrahepatic portal vein thrombosis (PVT) can be visualized on ultrasound or CT as linear branching hypodensities or areas of altered enhancement reflecting changes in parenchymal perfusion.

Peliosis hepatis is commonly associated with a centrifugal enhancement pattern, where central enhancement progresses outward toward the periphery on contrast-enhanced imaging.

Liver Case Review Quiz

Quiz:

1. What is the typical signal intensity appearance of a hemangioma on a T2W MR image?
2. In a patient with cirrhosis, what imaging features on MRI or CT are classic for hepatocellular carcinoma (HCC)?
3. How do focal nodular hyperplasia (FNH) and hepatocellular adenoma (HCA) typically appear on the 20-minute hepatobiliary phase using a hepatobiliary contrast agent like gadoxetate disodium?
4. What does hypointensity on the 20-minute hepatobiliary phase favor according to LI-RADS in a patient at risk for HCC?
5. What is the typical enhancement pattern of cholangiocarcinoma on dynamic contrast-enhanced imaging?
6. What is the significance of portal vein tumor thrombus in a patient at risk for HCC?
7. What imaging finding is described as the “starry-sky” appearance on ultrasound of the liver?
   What is a common cause of the “hot spot sign” seen on CT, characterized by intense early enhancement of the medial segment left hepatic lobe?
8. What imaging finding on ultrasound or CT is consistent with intrahepatic portal vein thrombosis (PVT)?
9. What is the typical enhancement pattern associated with peliosis hepatis on contrast-enhanced imaging?
10. Compare and contrast the imaging features of focal nodular hyperplasia (FNH) and hepatocellular adenoma (HCA) on multiphase MRI with conventional extracellular contrast agents and hepatobiliary contrast agents, discussing the role of hepatobiliary agents in their differentiation.
11. Describe the LI-RADS classification system for evaluating liver lesions in patients at risk for hepatocellular carcinoma (HCC), including the major and ancillary features used for categorization and the implications of different LI-RADS categories.
12. Discuss the different causes and imaging appearances of diffuse liver disease, such as cirrhosis, hepatic steatosis, and hemochromatosis, highlighting key imaging features that help differentiate these conditions.
13. Explain the imaging characteristics of benign cystic liver lesions, including simple hepatic cysts, polycystic liver disease, biliary cystadenoma/cystadenocarcinoma, and biliary hamartomas (von Meyenburg complex), and how imaging helps in their diagnosis and differentiation.
14. Discuss the imaging findings associated with hepatic vascular disorders such as Budd-Chiari syndrome, portal vein thrombosis, and arterioportal shunts, and explain how these findings relate to the underlying pathophysiology.

Glossary of Key Terms:

1. Arterial Phase: The phase of contrast enhancement where the hepatic arteries and hypervascular lesions enhance brightly. Typically occurs within 20-30 seconds after contrast injection.
2. Budd-Chiari Syndrome (BCS): A condition characterized by obstruction of hepatic venous outflow, leading to passive hepatic congestion.
3. Capsule Appearance: An imaging feature seen on delayed phase contrast-enhanced imaging of liver lesions, where a rim of enhancement is visible around the lesion.
4. Centrifugal Enhancement: An enhancement pattern where contrast fills in from the center of a lesion outwards towards the periphery.
5. Centripetal Enhancement: An enhancement pattern where contrast fills in from the periphery of a lesion inwards towards the center. Classic for hemangiomas.
6. Cholangiocarcinoma: A malignant tumor arising from the biliary tree.
7. Cirrhosis: Chronic liver disease characterized by diffuse fibrosis and the formation of regenerating nodules, leading to impaired liver function.
8. Delayed Phase: A phase of contrast enhancement acquired several minutes (typically 3-5 minutes or later for conventional agents, or 20 minutes for hepatobiliary agents) after contrast injection. Also known as equilibrium phase for extracellular agents.
9. Dynamic Contrast Enhancement: The evaluation of tissue enhancement over time after the intravenous administration of a contrast agent, typically involving multiple imaging phases.
10. Fat Saturation (FS): An MRI technique used to suppress the signal from fat, making other tissues more conspicuous.
11. Focal Nodular Hyperplasia (FNH): A benign liver tumor of hepatocellular origin, typically hypervascular and containing a central scar.
12. Gadoxetate Disodium (Eovist): A hepatobiliary-specific gadolinium-based MRI contrast agent that has both extracellular and hepatocyte uptake.
13. Giant Cavernous Hemangioma (GCA): A large benign vascular tumor of the liver.
14. Glisson Capsule: The fibrous connective tissue capsule surrounding the liver.
15. Hepatobiliary Phase: The phase of MRI enhancement using a hepatobiliary contrast agent, typically acquired 20 minutes after injection, where the contrast agent has been taken up by functioning hepatocytes.
16. Hepatocellular Adenoma (HCA): A benign liver tumor of hepatocellular origin, typically hypervascular.
    Hepatocellular Carcinoma (HCC): A malignant tumor arising from hepatocytes, commonly seen in patients with cirrhosis.
17. Hemosiderosis: A form of secondary hemochromatosis characterized by iron deposition in the reticuloendothelial system, including the liver and spleen.
    Hypervascular: Describes a lesion that enhances more than the surrounding normal parenchyma on the arterial phase of contrast-enhanced imaging.
18. Hypoattenuating/Hypodense: Describes an area that appears darker than the surrounding tissue on CT.
    Hypointense: Describes an area that appears darker than the surrounding tissue on MRI.
    In-Phase/Out-of-Phase Imaging: MRI techniques used to detect and quantify microscopic fat within tissues based on the different precession frequencies of water and fat protons.
19. Kasabach-Merritt Syndrome: A rare disorder associated with large vascular tumors (such as giant cavernous hemangiomas) and severe thrombocytopenia due to platelet sequestration.
    Laceration: A tear or cut in the liver parenchyma, often due to trauma.
20. LI-RADS (Liver Imaging Reporting and Data System): A standardized system for interpreting and reporting liver imaging findings in patients at risk for HCC.
21. Macronodularity: The presence of large regenerating nodules in the liver, a feature of cirrhosis.
22. Micronodularity: The presence of small regenerating nodules in the liver, a feature of cirrhosis.
23. Nutmeg Liver: A mottled appearance of the liver parenchyma on imaging due to passive hepatic congestion.
24. Peliosis Hepatis: A rare benign vascular disorder characterized by dilated sinusoids and blood-filled cavities within the liver.
25. Peritoneal Carcinomatosis: The spread of cancer to the peritoneum, the lining of the abdominal cavity.
    Polycystic Liver Disease (PLD): A genetic disorder characterized by the presence of multiple cysts in the liver, often associated with autosomal dominant polycystic kidney disease (ADPCKD).
26. Portal Hypertension: Increased pressure in the portal vein system.
    Portal Vein Thrombosis (PVT): The formation of a blood clot in the portal vein.
27. Posttransplant Lymphoproliferative Disorder (PTLD): A heterogeneous group of disorders ranging from benign hyperplasia to poor-differentiated lymphoma, seen in transplant recipients.
28. Pyogenic Abscess: A collection of pus in the liver, typically caused by bacterial infection.
    Regenerative Nodule: A nodule of regenerating hepatocytes, often seen in cirrhosis.
29. Resistive Index (RI): A Doppler ultrasound measurement that reflects the resistance to blood flow within a vessel.
30. Right Posterior Hepatic Notch Sign: A focal indentation of the posteroinferior surface of the right hepatic lobe in cirrhosis.
31. Siderotic Nodule: An iron-containing nodule in the liver, often seen in cirrhosis.
    Spin-Echo (SE): An MRI pulse sequence that is less susceptible to magnetic field inhomogeneities and artifacts than gradient-echo sequences.
32. Steatosis: The accumulation of fat within the liver parenchyma.
33. Subcapsular Hematoma: A collection of blood between the liver capsule and the liver parenchyma.
34. Susceptibility Artifact: Distortion or signal loss on MRI caused by differences in magnetic susceptibility between adjacent tissues.
35. T1W (T1-Weighted): An MRI pulse sequence that emphasizes T1 relaxation properties of tissues.
36. T2W (T2-Weighted): An MRI pulse sequence that emphasizes T2 relaxation properties of tissues.
37. Tardus et Parvus Waveform: A Doppler ultrasound waveform characterized by a delayed arterial upstroke and decreased peak velocity, indicative of stenosis upstream.
38. Transient Hepatic Attenuation Difference (THAD): A focal or geographic area of altered parenchymal enhancement seen on CT, often due to changes in perfusion.
39. Transient Hepatic Intensity Difference (THID): A focal or geographic area of altered parenchymal signal intensity seen on MRI, often due to changes in perfusion.
40. Venous Phase: The phase of contrast enhancement where the portal and hepatic veins are opacified and the liver parenchyma enhances. Typically occurs 60-80 seconds after contrast injection.
41. Von Meyenburg Complex: Also known as biliary hamartomas, these are numerous small, benign cystic lesions scattered throughout the liver, resulting from abnormal embryologic development of the biliary ductal plate.
42. Washout Appearance: An imaging feature seen on delayed phase contrast-enhanced imaging of liver lesions, where the lesion enhances less than the surrounding liver parenchyma.