1  Answers: A4; B6; C7; D3; E1; F10; G2; H11; I9; J8; K5; L12.

An understanding of hepatic lobar and segmental anatomy is essential in reporting to aid treatment planning. The liver is divided into right, left, and caudate lobes. The right lobe is subdivided into anterior and posterior segments and the left lobe into medial and lateral segments. The main hepatic veins are located in between segments of the liver. The portal triads (composed of the portal veins, hepatic arteries, and bile ducts) are located within segments of the liver. The Bismuth-Couinaud system is commonly used to provide a segmental nomenclature for localizing focal hepatic lesions. Vertically oriented planes along the right, middle, and left hepatic veins are maintained. These vertical planes intersecting a horizontal plane at the level of the right and left portal veins separate the liver into nine segments.

Segment I is the caudate lobe, located posterior to the fissure for the ligamentum venosum. Functionally, it is an autonomous part of the liver and has a separate blood supply, venous drainage, and biliary drainage.

The fissure for the ligamentum venosum is a coronally or obliquely oriented well-defined fissure. A normal variant accessory or replaced left hepatic artery from the left gastric artery can be seen running through this fissure.

The interlobar fissure (fissure of the gallbladder) separates the right and left lobes.

The fissure for the falciform ligament (fissure for the ligamentum teres) is located in the inferior aspect of the left hepatic lobe. The remnant umbilical vein “recanalizes” in the setting of portal hypertension and can be seen running through this fissure.

References: Boll DT, Merkle EM. Liver: normal anatomy, imaging techniques, and diffuse diseases. In: Haaga JR, Lanzieri CF, Gilkeson RC (eds). CT and MRI imaging of the whole body, 5th ed. Philadelphia, PA: Elsevier, 2009:1953–2040.

Ding A, Kulkarni N, Fintelmann FJ, et al. Liver: normal anatomy and examination techniques. In: Gore RM, Levine MS (eds). Textbook of gastrointestinal radiology, 4th ed. Philadelphia, PA: Elsevier Saunders, 2015:1471–1497.

2  Answer D.The liver is diffusely hyperdense in this patient with cardiac disease. Normal density is 45 to 65 HU on a noncontrast CT scan obtained with conventional kVp of 120.  At visual inspection, it should appear similar to the spleen, which is about 35 to 55 HU. Diffuse hepatic hyperdensity can be caused by iodine deposition in patients treated with the cardiac antiarrhythmic drug amiodarone, which is 37% iodine by weight. This hyperdensity does not always indicate toxicity, and patients may be asymptomatic. However, if injury is severe, the patient may develop steatosis and cirrhosis. If there is pulmonary involvement, interstitial fibrosis and high-density pulmonary opacities may be seen.

Other causes of diffuse hepatic hyperdensity include hemochromatosis (iron deposition), Wilson disease (copper deposition), gold therapy, and glycogen storage disease. Thorotrast was associated with deposition of high density in a characteristic reticular pattern within the liver and spleen. The use of Thorotrast, a radioactive contrast agent, was discontinued in the 1950s when it was discovered to be carcinogenic. Total parenteral nutrition and radiation therapy are more commonly causes of steatosis and decreased liver density. Hepatorenal syndrome is unrelated to liver hyperdensity. It refers to renal failure caused by cirrhosis or fulminant hepatitis, leading to portal hypertension and ascites.

References: Coy, DL, Kolokythas O. Chapter 9: Liver and biliary. In: Lin E, Coy DL, Kanne JP (eds). Body CT: the essentials. New York, NY: McGraw-Hill, 2015.

Morgan T, Qayyum A, Gore RM. Chapter 89: Diffuse liver disease. In: Gore RM, Levine MS (eds). Textbook of gastrointestinal radiology, 4th ed. Philadelphia, PA: Elsevier/Saunders, 2015:1629–1675.

3  Answer A.MRI is the imaging modality of choice to evaluate focal hepatic lesions, as reflected in the ACR Appropriateness Criteria. This series of questions reviews the classic appearances of some primary hepatic tumors on MRI. There is a well-circumscribed lesion in hepatic segment VII, which is very bright on the T2W image approaching signal intensity of cerebrospinal fluid, consistent with the “light bulb” sign. The mass demonstrates peripheral, nodular, discontinuous enhancement, followed by centripetal fill-in on delayed phase. These features are diagnostic for cavernous hemangioma. Fill-in may be partial or complete in hemangiomas. Hemangiomas are dilated venous channels with hepatic arterial supply. The great majority are asymptomatic and require no follow-up or treatment.

References: Boland GWL, Halpert RD. Chapter 6: Liver. In: Boland GWL, Halpert RD (eds). Gastrointestinal imaging: the requisites, 4th ed. Philadelphia, PA: Elsevier/Saunders, 2014:218–290.

Cogley JR, Miller FH. MR imaging of benign focal liver lesions. Radiol Clin North Am 2014;52:657–682.

4  Answer D.This mass is a hepatocellular carcinoma (HCC). Signal intensity of the mass in segment VIII is similar to surrounding liver on both noncontrast T1W and T2W images, a clue that the tumor may be of hepatocellular origin (i.e., an HCC, focal nodular hyperplasia, or hepatocellular adenoma). The mass enhances on the arterial phase and demonstrates washout appearance as well as capsule appearance on delayed phase. These features are classic for HCC in this patient with cirrhosis. Additional imaging features that may be also present in HCC are intralesional fat, restricted diffusion, and portal vein tumor thrombus.

MRI is the most sensitive and specific imaging modality for the diagnosis of HCC. Awareness of patient demographics and clinical history is critical in the evaluation of hepatic lesions. In the presence of cirrhosis, a high index of suspicion for HCC should be maintained for any enhancing liver lesion. Washout appearance is an important imaging feature in the identification of classic HCC. A mass demonstrates washout appearance if it initially appears iso- to hyperintense to surrounding liver and then appears hypointense to surrounding liver on a later phase. “Washout” is often a misnomer because this appearance is predominantly due to increase in enhancement of the surrounding liver rather than loss of signal intensity by the mass itself.

References: ACR Appropriateness Criteria: Liver lesion— initial characterization. American College of Radiology website. https://acsearch.acr.org/docs/69472/Narrative. Published 1998. Updated 2014. Accessed April 4, 2015.

Choi JY, Lee JM, Sirlin CB. CT and MR imaging diagnosis and staging of hepatocellular carcinoma: Part II. Extracellular agents, hepatobiliary agents, and ancillary imaging features. Radiology 2014;273(1):30–50.

5  Answer E.This neoplasm is a mass-forming cholangiocarcinoma. The MRI demonstrates a large mass that shows sparse early enhancement and then heterogeneous progressive enhancement on later phases. Delayed enhancement is a feature suggesting a desmoplastic tumor such as a cholangiocarcinoma. Its hypointensity is very distinct from the surrounding liver parenchyma on T1W imaging, a clue that the tumor may not be of hepatocellular origin.

Cholangiocarcinoma is a malignant tumor arising from the biliary tree and represents the second most common primary malignancy of the liver. It can be categorized into three types based on morphology: mass-forming, periductal infiltrating, and intraductal growth types. Mass-forming cholangiocarcinoma may be seen with or without biliary ductal dilation. There may be associated hepatic capsular retraction, satellite nodules, and vascular encasement. It can be mistaken for a hemangioma due to its progressive delayed enhancement but lacks the well-defined puddles of peripheral discontinuous nodular enhancement seen with cavernous hemangiomas. In addition, the mass lacks the characteristic “light bulb” T2 hyperintensity of a hemangioma.

References: Chung YE, Kim MJ, Park YN, et al. Varying appearances of cholangiocarcinoma: radiologic-pathologic correlation. Radiographics 2009;29(3):683–700.

Sainani NI, Catalano OA, Holalkere NS, et al. Cholangiocarcinoma: current and novel imaging techniques. Radiographics 2008;28(5):1263–1287.

6  Answer C.This patient has a focal nodular hyperplasia (FNH). There is an arterial-enhancing mass which retains contrast agent at 20 minutes on this MRI performed with Eovist hepatobiliary contrast agent. The mass is isointense on precontrast T2W image with exception of the small central scar, which is classically T2 hyperintense. All of the other answer choices are typically hypointense to the liver on the hepatobiliary phase.

If a conventional extracellular contrast agent (not shown here) is used, homogeneous arterial enhancement is seen, classically followed by venous and delayed phase isointensity. A prominent feeding vessel extending toward the central scar is sometimes identified on arterial phase. The central scar may enhance on the delayed phase when conventional extracellular contrast is used. Focal nodular hyperplasia is a benign mass representing a heptaocellular hyperplastic response to a pre-existing arterial malformation. It is most common in women of reproductive age. In 20% of cases, there are multiple lesions.

Differentiation from hepatocellular adenoma (HCA), another benign hypervascular hepatocellular tumor found in young women, is important as no other treatment is required for FNH, while HCA may require follow-up or intervention for hemorrhage, or rarely, malignant transformation. MRI with hepatobiliary contrast agent has been found to be highly sensitive and specific for differentiating FNH and HCA in this patient population. Because FNH contains normal functioning hepatocytes, it accumulates hepatobiliary contrast agent and remains iso- to hyperintense to the liver on 20-minute hepatobiliary phase images. In contradistinction, HCAs are hypointense on hepatobiliary phase.

References: Khosa F, Khan AN, Eisenberg RL. Hypervascular liver lesions on MRI. AJR Am J Roentgenol 2011;197(2):W204–W220.

Silva AC, Evans JM, McCullough AE, et al. MR imaging of hypervascular liver masses: a review of current techniques. Radiographics 2009;29(2):385–402.

7  Answer D.This is the expected appearance of a hepatocellular carcinoma (HCC) on an MRI performed with hepatobiliary contrast agent. The mass in the left lobe of the liver shows arterial enhancement. It is dark compared to surrounding liver on the hepatobiliary phase. There is evidence of cirrhosis with bands of fibrosis which are also hypointense on hepatobiliary phase. Other hypervascular masses such as hemangioma, hepatocellular adenoma (HCA), focal nodular hyperplasia (FNH), and metastasis are significantly less common in the cirrhotic liver compared to the general population. The lesion is isointense to the liver on T2 images, with no evidence of “light bulb” T2 hyperintensity to suggest a hemangioma. This 51-year-old man is not in the right demographic for HCA or FNH, lesions which most commonly occur in premenopausal women.

The role of hepatobiliary contrast agents in the patients at risk for HCC continues to evolve. In general, isointensity or hyperintensity on hepatobiliary phase is reassuring, suggestive of a benign finding such as regenerative nodule, dysplastic nodule, or arterioportal shunt with transient hepatic intensity difference (THID). Borders of an HCC may appear more sharply marginated on hepatobiliary phase than on other sequences, helping in the delineation and measurement of heterogeneous, infiltrative lesions.

References: Choi JY, Lee JM, Sirlin CB. CT and MR imaging diagnosis and staging of hepatocellular carcinoma: Part II. Extracellular agents, hepatobiliary agents, and ancillary imaging features. Radiology 2014;273(1):30–50.

Jhaveri K, Cleary S, Audet P, et al. Consensus statements from a multidisciplinary expert panel on the utilization and application of a liver-specific MRI contrast agent (gadoxetic Acid). AJR Am J Roentgenol 2015;204(3):498–509.

8  Answer D.If a hepatobiliary agent such as gadoxetate disodium (Eovist—Bayer HealthCare) is used, hypointensity on the 20-minute hepatobiliary phase is considered an ancillary feature that favors HCC according to LI-RADS (Liver Imaging Reporting and Data System). Ancillary features may upgrade suspicion for hepatocellular carcinoma no higher than category LI-RADS category 4 (probably HCC). Some other ancillary features that would favor HCC include diffusion restriction, nodule-in-nodule architecture, intralesional fat, and growth less than threshold.

LI-RADS was developed by a multidisciplinary committee supported by the American College of Radiology (ACR) to standardize interpretation and reporting of multiphase CT and MRI exams of the liver. LI-RADS is applicable to the patient population with cirrhosis or chronic hepatitis B and/or C, who are at risk for hepatocellular carcinoma (HCC). The algorithm for LI-RADS version 2014 is an interactive graphic on the ACR Web site with definitions, descriptions, and examples. LI-RADS categories range from LR-1 (100% certainty that observation is benign) to LR-5 (100% certainty that observation is HCC). When an observation does not meet criteria for other categories, it is designated LR-3 indicating intermediate probability for HCC.

Reproduced with permission from the American College of Radiology. Liver Imaging Reporting and Data System version 2014. Accessed April 2015, from http://www.acr.org/Quality-Safety/Resources/LIRADS.

Major features for HCC in LI-RADS include “washout,” “capsule,” and threshold growth. Arterial enhancement and size thresholds are also included in major criteria, with masses ≥2 cm most worrisome. “Washout” and “capsule” specified in quotation marks (or washout appearance and capsule appearance) are the terms preferred by LI-RADS. This serves as a reminder that these terms are visual cues, which do not necessarily represent true loss of contrast enhancement on imaging or a true capsule at pathology.

Hepatobiliary phase hypointensity is not considered “washout.” On an MRI performed with a hepatobiliary contrast agent, it may only be appropriate to refer to washout appearance on the earliest venous phases in the dynamic portion of the exam (before 3 minutes) before the hepatobiliary phase dominates.

References: American College of Radiology. Liver Imaging Reporting and Data System version 2014. Accessed July 2015, from http://www.acr.org/Quality-Safety/Resources/LIRADS

Liu YI, Shin LK, Jeffrey RB, et al. Quantitatively defining washout in hepatocellular carcinoma. AJR Am J Roentgenol 2013;200(1):84–89.