Liver Imaging Reporting and Data System (LI-RADS) is both a set of standardized terminology and a classification system for imaging findings in liver lesions. The LI-RADS score for a liver lesion is an indication of its relative risk for hepatocellular carcinoma (HCC).

The classification system is meant to be used in livers that have risk factors for HCC (e.g. cirrhotic livers, chronic HBV without cirrhosis). LI-RADS is not meant to be used in patients <18 years old, those with cirrhosis due to congenital hepatic fibrosis, and those with cirrhosis due to vascular disorders (e.g. Budd-Chiari syndrome).

It has been proposed with the aim to decrease the variability in the interpretation of liver lesions in at-risk patients. Standardization also helps interpret therapeutic performance. The scoring system also helps communicate more clearly to non-hepatologists the degree of suspicion attached to liver lesions in their patients.

(non-rim) arterial phase hyperenhancement
- hyperenhancement: enhancement in the arterial phase is definitely greater than that of background liver
- if unsure, classify as iso-enhancing
nonperipheral "washout"
- a visual assessment of relative hypointensity of the lesion compared with background liver on the portal venous and delayed phases
- with Gadoxetate there must be hypointensity in the portal venous phase
enhancing capsule/pseudocapsule
- peripheral rim of smooth hyperenhancement seen in the portal venous phase, transitional phase, or delayed phase
threshold growth
- diameter increase ≥50% increase in ≤6 months
  - other prior criteria are now considered subthreshold growth, an ancillary feature
    - if prior exam >6 months, diameter ≥100% increase
    - a new lesion ≥10 mm in <24 months
- threshold growth should be compared on similar sequences between studies
- only apply this criterion if the lesion is definitely a mass (e.g. not perfusion alteration)

Ancillary features

favoring malignancy, not HCC in particular
- ultrasound visibility as a discrete nodule
- subthreshold growth (see "threshold growth" in the major criteria section)
- corona enhancement
- fat sparing in a solid mass
- restricted diffusion
- mild-to-moderate T2 hyperintensity
- iron sparing in a solid mass
- transitional phase hypointensity
- hepatobiliary phase hypointensity
favoring HCC in particular
- nonenhancing "capsule"
- nodule-in-nodule architecture
- mosaic architecture
- fat in mass, more than adjacent liver
- blood products in mass
favoring benignity
- size stability ≥2 years
- size reduction
- homogeneous marked T2 hyperintensity
- homogeneous marked T2 or T2* hypointensity
- undistorted vessels
- parallels blood pool enhancement
- hepatobiliary phase isointensity

Classification

Major criteria imaging findings often lead directly to the assignment of the LI-RADS score. If the assignment is unclear, ancillary findings may be useful as a "tie-breaker".

The LI-RADS score ranges from LR-1 (favor benignity) to LR-5 (favor malignancy).

LR-1 (100% benign)

imaging features diagnostic of a benign entity:
- cyst
- hemangioma
- vascular anomaly
- perfusion alteration
- hypertrophic pseudomass
- confluent hepatic fibrosis
- focal scar
definite disappearance at follow-up in the absence of treatment is also indicative of LR-1

LR-2 (probably benign)

entities are similar to LR1, but the appearance is highly suggestive of the entity instead of 100% diagnostically certain
- atypical appearance of benign entities may be categorized as LR2
- LR2 cirrhosis-associated nodule is also included

LR-3 (intermediate probability for HCC)

not a definitely benign entity, but not definitely HCC
includes entities with the following features:
- not a definite mass
- mass with hepatic arterial phase iso- or hypoenhancement
  - <20 mm with no more than one of the following:
    - nonperipheral "washout"
    - capsule
    - threshold growth
- mass with hepatic arterial phase hyperenhancement
  - <20 mm with no "washout," capsule, or threshold growth

LR-4 (probably HCC)

no arterial phase hyperenhancement
- <20 mm
  - two or more of the following
    - non-peripheral "washout"
    - enhancing capsule
    - threshold growth
- ≥20 mm
  - one or more of the following
    - non-peripheral "washout"
    - enhancing capsule
    - threshold growth
non-rim arterial phase hyperenhancement
- <10 mm
  - one or more of the following
    - non-peripheral "washout"
    - enhancing capsule
    - threshold growth
- 10-19 mm
  - enhancing "capsule", but does not meet threshold growth or washout criteria
- ≥20 mm
  - no major suspicious features:
    - non-peripheral "washout"
    - enhancing capsule
    - threshold growth

LR-5 (100% definite HCC)

non-rim arterial phase hyperenhancement
- 10-19 mm
  - single major suspicious feature (washout or threshold growth), excluding enhancing "capsule" (LR-4)
  - two or more of the following
    - threshold growth
    - enhancing capsule
    - nonperipheral "washout"
- ≥20 mm
  - one or more of the following
    - threshold growth
    - enhancing capsule
    - nonperipheral "washout"

Special categories

LR-M for liver lesions that are probably or definitely malignant, but not an appearance compatible with HCC. Examples of this include:

targetoid mass
non-targetoid mass with
- infiltrative appearance
- marked diffusion restriction
- necrosis or severe ischemia
- other appearance that in the radiologists' judgment suggests a non-HCC malignancy

LR-NC (LR-non-categorizable) for lesions in which the technical quality of the MRI does not allow evaluation of the major features.

LR-TIV for unequivocal enhancing soft tissue invading the portal vein, regardless of whether an underlying parenchymal mass is visible. This is important to report since it is a contraindication to liver transplantation. Malignancies other than HCC can invade the portal venous system.

Treatment and prognosis

Suggested management:

LR-1: continued routine surveillance
LR-2: continued routine surveillance, consider repeat diagnostic imaging in six months or less
LR-3: repeat or alternative diagnostic imaging in 3-6 months
LR-4: multidisciplinary team discussion for tailored workup, may include biopsy
LR-5: diagnosis confirmed - plan treatment
LR-NC: repeat or alternative diagnostic imaging in three months or less

Practical points

ancillary features can upgrade or downgrade a lesion one category but cannot upgrade a lesion to LR-5
if there are no LR-4 or LR-5 lesions, then LR-3 lesions should be reported, otherwise reporting of LR-3 lesions is at the radiologist's discretion (they should be reported if previously LR-4 or LR-5)
late hepatic arterial phase is preferred for evaluation of arterial hyperenhancement
for masses with nodule-in-nodule appearance, measure the entire mass