Definition:

• The largest diameter (outer edge to outer edge) of an observation is ≥ 20mm. 

Usage

• Applies to observations that are neither definitely nor probably benign, are not suspicious for a non-HCC malignancy, and do not have tumor in vein
• Diameter >20mm is a major feature for categorization of masses

• Masses with diameter of >20mm may be categorized LR-3, LR-4, or LR-5 depending on the presence of other major or ancillary features as shown in Table.
• Diameter should be measured in the sequence or phase in which the margins are most sharply demarcated and in which there is no anatomic distortion. If margins are sharply demarcated on more than one sequence or phase, do not measure in the arterial phase.
• Rationale: apparent diameter in the arterial phase is variable, depending on exact timing of image acquisition. Also, perilesional enhancement in the arterial phase might be misconstrued as part of hyperenhancing mass.

If unsure about feature:

• If observation has arterial phase hyperenhancement, characterize as Diameter 10-19mm
• If observation has arterial phase iso- or hypoehancement, characterize as Diameter<20mm

Background:

• Rationale: A threshold of > 20 mm in size was originally used in earlier TNM staging systems for T (tumor size) staging and by multiple imaging criteria (EASL, AASLD, etc) developed in and outside the United States for the diagnosis of HCC.  A threshold size of 20 mm is also important for defining UNOS stage 2 HCC.

• Unlike UNOS/OPTN, LI-RADS does not further distinguish between masses > 20 mm that are either smaller or larger than 5 cm.

 References:

Danet IM et al, Spectrum of MRI Appearances of untreated metastases of the liver. AJR Am J Roentgenol 2003; 181(3): 809-17

Cruite I et al, Imaging-based diagnostic systems for hepatocellular carcinoma. AJR Am J Roentgenol 2013; 201():41-55.

Wald C et al, New OPTN/UNOS Policy for Liver Transplant Allocation: Standardization of Liver Imaging, Diagnosis, Classification, and Reporting of Hepatocellular Carcinoma. Radiology 2013; 266(2):376-382