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Kanmaniraja et al. Hepatoma Res 2020;6:51 I http://dx.doi.org/10.20517/2394-5079.2020.46 Page 3 of 11

LI-RADS CT/MRI diagnostic algorithm is equally applicable to CT and MRI. It is important to note,
however, that the assigned categories may be discordant between the two modalities. Several studies have
demonstrated that the LI-RADS categories are discordant between CT and MRI in about 35%-70% of
[9]
cases . MRI categorizes more benign lesions as LR-1 compared to CT (25%-30% of those lesions were
categorized as LR-3 on CT) [11,12] . When excluding the LR-1 category, MRI-assigned categories are higher
compared to the CT-assigned categories (12%-31% of LR-5 observations on MRI were categorized as LR-4,
12% as LR-3, and 15%-29% were not seen on CT) [9,11,12] . The discrepancies in category assignment is
likely multifactorial, and they are related to inherent differences between the modalities, inter-reader
disagreements, and the fact that some of the imaging features are only assessable by MRI.

To maintain high specificity of the HCC diagnosis, the LI-RADS algorithm must be applied to a well-
defined at-risk target population with a high pretest probability of HCC [7,13] . It is essential that the patients
meet the inclusion criteria for LI-RADS patient population, and have none of the exclusion criteria. The
LI-RADS patient population includes patients with cirrhosis, chronic hepatitis B with or without cirrhosis,
and a personal history of HCC [7,13] . The exclusion criteria include patients < 18 years of age, those with
[8]
vascular causes of cirrhosis, or those with congenital hepatic fibrosis .
The LI-RADS CT/MRI algorithm is applied in a stepwise fashion beginning with LR-NC . This is followed
[7]
by LR-TIV, LR-1, LR-2, and LR-M. Once the above categories are excluded, the CT/MRI diagnostic table
is then used to assign an observation LR-3, LR-4, or LR-5 category. Observations with a pathological
diagnosis are reported as such and not assigned a LI-RADS category to avoid confusion and uncertainty
(i.e., pathology proven intrahepatic cholangiocarcinoma or pathology proven hemangioma). The exception
to this is in pathological proven benign or premalignant hepatocellular lesions such as regenerative or
[9]
dysplastic nodules, which are assigned LI-RADS categories . The rationale is that such lesions may evolve
over time and progress to frank malignancy.

The CT/MRI diagnostic table uses a combination of the major features [Figure 1] to assign LR-3, LR-4, and
LR-5 categories, with the option of applying ancillary features (AF) to adjust the final category. The LI-RADS
category can be upgraded or downgraded by one, if there are more than one AF favoring malignancy or
[14]
benignity, respectively . It is important to note that an LR-4 observation cannot be upgraded to LR-5
[14]
based on AF . The category is also not adjusted where there are ancillary features favoring both benignity
[14]
and malignancy .
CT/MRI diagnostic categories
LR-NC: not categorizable
Observations are included in this category when they cannot be meaningfully categorized because of
image omission and/or degradation, preventing assessment of one or more of its major features resulting
in the inability to differentiate categories in which cancer is unlikely (LR-1 or LR-2) from categories in
which cancer is likely (LR-4, LR-5, and LR-M) [7,15] . LR-NC should be applied only to observations that are
specifically affected by the limitation and not applied to the entire liver . Management in this category
[15]
includes a repeat diagnostic imaging usually within three months with the option of using an alternative
modality or contrast agent to improve diagnostic quality .
[16]
LR-TIV: definite tumor in vein
Observations in this category demonstrate definite enhancing soft tissue in vein, regardless of the presence
of parenchymal mass [Figure 2] [7,15] . Approximately 92% of observations are malignant . Approximately
[17]
80% of LR-TIV is attributed to HCC, and some intrahepatic cholangiocarcinoma (iCCA) and combined
[17]
HCC-cholangiocarcinoma (cHCC-CCA) may also cause tumor in vein . When a LR-5 parenchymal
observation is associated with TIV, it is reported as “LR-TIV, definitely due to HCC”, and, in the absence of