Definition:

• The largest diameter (outer edge to outer edge) of an observation is < 10 mm

Usage

• Applies to observations that are neither definitely nor probably benign, are not suspicious for a non-HCC malignancy, do not have tumor in vein, and have arterial phase hyperenhancement
• Diameter <10mm is a major feature for categorization of masses with arterial phase hyperenhancement

• Masses with diameter of < 10 mm may be categorized LR-3 or LR-4 depending on the presence of other major or ancillary features. As shown in Table, such masses cannot be categorized as LR-5.
• 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 hyper-enhancing mass.

If unsure about feature 

• Do characterize as Diameter <10mm

Background

• The diagnostic accuracy of CT or MR imaging for HCC decreases for smaller masses.  Observations <10mm are
  • Unlikely to be HCC
  • Difficult to characterize on CT or MR
  • Difficult to co-localize between imaging and resection/explant specimens
  • Not considered definite HCC (OPTN 5) according to  UNOS/OPTN policy

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