Liver Imaging Reporting and Data System (LI-RADS)
Review of LI-RADS for radiology board review. To download the free study guide on this topic click here. Prepare to succeed!
Show Notes/Study Guide:
CT/MRI Liver Imaging Reporting and Data System (LI-RADS)
Note this episode only pertains to diagnostic LI-RADS evaluation. update is anticipated in late 2024.
A Treatment Response LI-RADS
What is the overall point of LI-RADS?
LI-RADS exists to categorize CT and MRI imaging findings in terms of the risk of an imaging finding in the
liver for being a hepatocellular carcinoma (HCC). Whereas BI-RADS exists to categorize breast lesions in
terms of risk for all primary breast cancers, LI-RADS is specific for HCC risk.
What is the difference between an “observation” and a “lesion or nodule” in LI-RADS?
A focal abnormality seen on imaging is technically an “observation” per LI-RADS as these may or may not
represent a true “lesion” or “nodule”. For example, a perfusion anomaly may appear as a “lesion” or
“nodule” on initial imaging but is, in fact, not. So “observation” is used instead.
What are major features for diagnosis of HCC on CT or MRI according to LI-RADS?
Major criteria for diagnosis of HCC on LI-RADS include internal arterial hyperenhancement above
background liver enhancement followed by internal washout of enhancement relative to background
liver on the portal venous and delayed post-contrast phases. Additionally, an enhancing capsule that
appears as a peripheral rim of smooth hyperenhancement is also a major feature of HCC. Another major
feature of HCC is a diameter increase of at least 50% in six months or less, but this only applies if the
imaging finding is that of a mass and not something like aberrant perfusion.
On which phase of enhancement should an HCC be measured?
A hepatocellular carcinoma should be measured on whichever sequence best illustrates mass margins
and should be measured outer edge to outer edge. In general, measuring an HCC on arterial phase
imaging, or other sequences like DWI, is discouraged as margins are not typically best seen on these
sequences. When comparing size measurements over time, make sure to always compare
measurements obtained on the same post-contrast phase. For example, don’t compare measurements
made on a portal venous phase to a subsequent measurement made on a delayed phase sequence.
If pathology results are available, should a LI-RADS category for that finding still be reported?
No, and yes. If the diagnosis is histologically proven, the pathological diagnosis is reported without a LI-
RADS category. However, if the biopsied lesion remains uncertain or is a precursor lesion to HCC such as
a dysplastic or regenerative nodule, both the pathology diagnosis and the LI-RADS score should be
reported.
True or false? HCCs can show internal fat.
True. While not specific for HCC, internal fat is a feature that can be seen with HCC and is a feature that
favors HCC compared to many other hepatic masses. Internal fat, greater than adjacent liver, is reported
to be an ancillary feature that favors HCC versus other hepatic malignancies.
1LI-RADS. Matt Covington, MD
Listen to the associated podcast episodes available at theradiologyreview.com or on your favorite
podcast directory.
What are ancillary features of a hepatic mass that favor benignity rather than an HCC?
Stability or reduction in size over at least 2 years or greater favors a benign hepatic mass rather than
HCC. Marked T2 homogeneous internal hyper- or hypo-intensity are both features that favor a benign
mass rather than an HCC as well as marked and homogeneous T2* hypointensity. A mass that mirrors
blood pool enhancement levels, and/or a mass that is isointense on hepatobiliary phase sequences is
favored to be benign.
What are the imaging features that would categorize an imaging finding as category LR-1 in LI-RADS?
LR-1 represents a 100% benign lesion. Imaging features diagnostic of a benign entity include a benign
hepatic cyst, hemangioma, perfusion alteration, focal scar, and confluent hepatic fibrosis. Lesions that
definitively disappear at follow-up without treatment are also considered LR-1.
What is the imaging appearance of confluent hepatic fibrosis?
Typically seen in a cirrhotic liver, confluent hepatic fibrosis is most common in the medial and anterior
segments of the liver involving hepatic segments 4, 7, or 8. Confluent hepatic fibrosis often appears
wedge-shaped, radiating from the porta hepatis out to the capsular surface with largest extent of
involvement peripherally. Mild capsular retraction or a mild concave peripheral margin may be seen.
Given the fibrosis, this should show progressive enhancement most pronounced on delayed phase
images on CT or MRI compared to normal liver background. On CT, areas of confluent hepatic fibrosis
typically appear hypodense on non-contrast imaging. On MRI, areas of confluent hepatic fibrosis
typically appear moderately T2 hyperintense with no internal fat signal intensity. While confluent
hepatic fibrosis and cholangiocarcinoma can both show capsular retraction, cholangiocarcinoma shows
arterial hyperenhancement and generally appears more mass-like than does confluent hepatic fibrosis.
Lastly, intrahepatic biliary ductal dilatation is more commonly seen with cholangiocarcinoma than with
confluent hepatic fibrosis.
How does an LR-2 finding differ from an LR-1 finding in LI-RADS?
LR-2 lesions are “probably benign”, whereas LR-1 lesions are 100% benign. LR-2 includes entities that are
highly suggestive of being benign but lack full diagnostic certainty. Atypical appearances of benign
entities and cirrhosis-associated nodules also fall under LR-2.
What are imaging features of a LR-2 cirrhosis-associated nodule?
To be classified as a LR-2 cirrhosis-associated nodule, all of the following imaging findings must be
present: diameter less than 20 mm but be distinctly larger than background cirrhotic nodules,
homogeneously enhances the same as background cirrhotic nodules in all phases, differs from
background cirrhotic nodules by having up to moderate hyperattenuation on CT, having up to moderate
T1 hyperintensity, and/or having mild, moderate, or marked T2 or T2* hypointensity.
What imaging features define an LR-3 finding in LI-RADS, and why is it considered intermediate
probability for hepatocellular carcinoma?
LR-3 indicates an intermediate probability of HCC. It includes entities that are neither definitely benign
nor definitively HCC. Imaging features include:
- No definite mass or a mass with iso- or hypoenhancement during the hepatic arterial phase.
2LI-RADS. Matt Covington, MD
Listen to the associated podcast episodes available at theradiologyreview.com or on your favorite
podcast directory.
- Mass smaller than 20 mm with no more than one suspicious feature defined as non-peripheral
washout, distinct capsule, or threshold growth which was previously described as at least 50% increase
in size in six-months or less.
- Mass with arterial phase hyperenhancement under 20 mm without additional major features of
washout, a distinct capsule, or meeting the growth threshold just described.
What are the key characteristics of an LR-4 mass in LI-RADS, which are considered "probably HCC"?
LR-4 indicates a probable hepatocellular carcinoma (HCC). These are divided into two major diagnostic
decision trees based on whether a mass has no arterial phase hyperenhancement or shows non-rim
arterial phase hyperenhancement.
No arterial phase hyperenhancement:
- Mass <20 mm with two or more of these features: non-peripheral washout, enhancing capsule, or
threshold growth.
- Mass ≥20 mm with at least one of the features described above.
Non-rim arterial phase hyperenhancement:
-Mass <10 mm with one or more of the following: non-peripheral washout, enhancing capsule, or
meeting threshold growth of at least 50% size increase in six months or less.
-Mass 10-19 mm must show an enhancing capsule but does not show washout or meet threshold
growth.
-Mass ≥20 mm has no other major features such as non-peripheral washout, an enhancing capsule, or
meeting threshold growth.
What defines an LR-5 mass in LI-RADS, and how is it certain for HCC?
LR-5 is 100% diagnostic of HCC. The mass presents with:
- Non-rim arterial phase hyperenhancement.
- For a mass measuring 10-19 mm, if there is an enhancing capsule this mass must also show non-
peripheral washout and meet threshold growth of at least 50% size increase in six months or less. If
there is no enhancing capsule, then either non-peripheral washout or threshold growth is sufficient.
- For a mass ≥20 mm, one or more of the following must be present: non-peripheral washout, an
enhancing capsule, or threshold growth.
What is the LI-RADS M (LR-M) category?
LR-M is used for hepatic lesions that are at least probably malignant but show an appearance unlikely to
be HCC. For example, highly infiltrative hepatic masses, or masses with marked restricted diffusion on
MRI.
What is the LI-RADS Tumor in Vein (LR-TIV) category?
If there is enhancing soft tissue that unequivocally invades the portal vein, whether due to HCC or other
hepatic malignancy, LR-TIV should be included to indicate this contraindication to liver transplantation.
3LI-RADS. Matt Covington, MD
Listen to the associated podcast episodes available at theradiologyreview.com or on your favorite
podcast directory.
What is category LI-RADS non-categorizable (LR-NC)?
LR-NC is used when the technical quality of imaging does not allow evaluation of major imaging features
of HCC. For example, imaging that does contain the required phases of enhancement would be
categorized as LR-NC.
Final note: There are many ancillary imaging features of benign or malignant hepatic masses that are not
fully addressed in this episode because there are so many of them. These can include co-existing
findings on ultrasound, presence of iron or blood products within a mass, and so forth.
However, LI-RADS is primarily driven by the major criteria of HCC which are described in this episode. I
think it is less likely that the Core exam will test you on the variety of ancillary features versus the major
criteria. For this reason, as well, I have focused on the major criteria in this episode.
I would remember, however, that ancillary features come into play for findings that are equivocal
between LI-RADS categories. These ancillary features can be used to upgrade or downgrade a lesion by
one LI-RADS category depending on whether ancillary imaging features are potentially concerning or
reassuring. It is also important to remember that while ancillary imaging features can upgrade or
downgrade an imaging finding by one LI-RADS category, such as LR-3 to LR-4, or LR-4 to LR-3, ancillary
imaging features can never upgrade a LR-4 mass to LR-5.
