Definition:

• The largest diameter (outer edge to outer edge) of an observation is ≥ 10 mm and ≤ 19mm.

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 10-19mm is a major feature for categorization of masses with arterial phase hyperenhancement

• Masses with diameter of 10-19mm may be categorized 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 

• Characterize as Diameter <10mm if unsure if >=10mm
• Characterize as Diameter 10-19mm if unsure if >=20mm

Background

• Rationale: The diagnostic accuracy of CT or MR imaging for HCC decreases for smaller masses. Thus, to achieve higher specificity, more stringent criteria are used for small, 10-19 mm observations: two additional major features are required to reach LR-5, compared to one major feature for observations > 20 mm to reach LR-5. A distinction between HCC below 20 mm and those at least 20 mm in size stems from the Milan Criteria, which is incorporated into the UNOS/OPTN criteria, and has implications for liver transplant allocation.

• For nodules from 10-19 mm, UNOS/OPTN requires both washout appearance and capsule appearance for an OPTN class 5A designation, OR only diameter increase for a class 5A-g (LR-5g) designation

References:

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

Marrero JA et al, Improving the prediction of hepatocellular carcinoma in cirrhotic patients with an arterially enhancing liver mass. Liver Transpl 2005; 11(3): 281-289.

Varela M et al, Hepatocellular carcinoma in the setting of liver transplantation. Liver Transpl 2006; 12(7): 1028-36

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