Organ Procurement and Transplantation Network (OPTN) classification

Organ Procurement and Transplantation Network (OPTN) is the unified transplantation network in the United States and runs under the administration of United Network for Organ Sharing (UNOS). OPTN classification is the part of thean imaging policy of UNOS that consists of in order to determine the eligibility and priority for liver transplantation:

• minimal technical recommendations for dynamic contrast-enhanced imaging of the liver in CT and MRI
• recommended imaging policies
• mandatory diagnostic criteria of hepatocellular carcinoma (HCC) 
• reporting requirements (for example: standardized language)
• requirements for image interpretation at OPTN transplantation centers. 

The main difference between LI-RADS and OPTN classification is that the former is a comprehensive imaging diagnostic system for all patients at risk for HCC, and the latter is the part of the above described policy and applicable to patients with HCC considered for liver transplantation. 

Classification

UNOS refers to LI-RADS for the definitions of OPTN classes 1 through 4, although the latest (LI-RADS v2014) includes key modifications to achieve congruence between LR-5 and OPTN class 5. There is one extra OPTN class, class 0, which describes an incomplete or technically inadequate study and requires a repeat study.

The most important class of the classification is the class 5, that includes untreated and treated definitive HCC and has several subclasses, based on the appearance and the lesion size.

The subclasses are (here only size noted):

• 5A: size: 10-19 mm
• 5B: size: 20-50 mm
• 5X: size: > 50 mm or tumor in vein
• 5T: for treated definite HCC

There are more diagnostic criteria and several cases where ancillary features and then tie-breaking rules have to be applied to adjust category.

For a complete list of classification criteria and a detailed comparison of LI-RADS and OPTN classification, please visit the corresponding link in the references section to the American College of Radiology.