CT/MRI Liver Imaging Reporting and Data System (LI-RADS) is an algorithm for diagnosing and staging hepatocellular carcinoma (HCC) (CT/MRI Diagnostic LI-RADS) or assessing the response of HCC to locoregional treatment (CT/MRI Treatment Response LI-RADS) using CT or MRI with extracellular contrast agents or MRI with hepatobiliary contrast agents³.

The current version is CT/MRI LI-RADS v2018 with a separate CT/MRI Treatment Response LI-RADS v2024 expected in late 2024 ³. The article below relates specifically to CT/MRI Diagnostic LI-RADS v2018. For other LI-RADS algorithms see: LI-RADS (overview).

Terminology

Focal abnormalities are referred to as "observations" in LI-RADS rather than lesions or nodules, as each observation may not be a true lesion or nodule but could reflect perfusion abnormalities or distortions of the background liver.

If an observation has been biopsied and the diagnosis is certain, the pathological diagnosis should be reported rather than the LI-RADS category. If the observation has been biopsied but the diagnosis is uncertain or it is an HCC precursor (regenerative or dysplastic nodule), the LI-RADS and the pathology diagnosis should be reported together.

Major criteria

• non-rim arterial phase hyperenhancement (APHE)

  • 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"

  • peripheral rim of smooth hyperenhancement seen in the portal venous phase, transitional phase, or delayed phase

• size

  • largest outer edge to edge dimension

  • should include "capsule" in measurement

  • measured on the phase or sequence in which margins are best seen

  • measurement on arterial phase or DWI is discouraged if margins better seen on other phases, as size on these may be over estimated

• 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

• favouring 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

• favouring HCC in particular

  • nonenhancing "capsule"

  • nodule-in-nodule architecture

  • mosaic architecture

  • fat in mass, more than adjacent liver

  • blood products in mass

• favouring 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 (favour benignity) to LR-5 (favour malignancy).

LR-1 (100% benign)

• imaging features diagnostic of a benign entity:

  • cyst

  • haemangioma

  • 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 categorised 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 ischaemia

  • other appearance that in the radiologists' judgement suggests a non-HCC malignancy

LR-NC (LR-non-categorisable) 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

See also

• RADS (Reporting and Data Systems)