Definition:

Peripheral rim of smooth hyper-enhancement in the portal venous phase or delayed phase that unequivocally is thicker or more conspicuous than the rims surrounding background nodule.

If unsure about capsule appearance:

Comments:

• Applies to observations that, in the portal venous phase or delayed phase, unequivocally have a peripheral rim of smooth hyperenhancement that is thicker or more conspicuous than the rims surrounding background nodule.
• Capsule appearance is a LI-RADS major feature for categorization of masses that are neither definite benign entities nor probable benign entities and that lack features of non-HCC malignancy or tumor in vein. For such masses, those with capsule appearance may be categorized LR-3, LR-4, or LR-5, depending on the observation’s arterial phase enhancement, diameter, and other features. As shown in Table, masses with capsule appearance but without arterial phase hyperenhancement cannot be categorized LR-5.
• The degree of enhancement of the “capsule” usually increases from early to later phases.
• The delayed phase may be superior to the portal venous phase for depicting this feature.
• Multiplanar images also may help demonstrate capsule appearance.
• The rim’s degree of arterial phase enhancement is not relevant for characterization of this feature.
• The rim’s attenuation/intensity on non-vascular phase images is not relevant for characterization of this feature.
• Rationale: To maintain congruency with OPTN definition of “capsule”, which is based only on vascular phase features.
• The terms capsule appearance and “capsule” (with quotation marks) are preferred over the term capsule.
• Rationale: the rim of enhancement does not always represent a true tumor capsule and may instead represent a pseudocapsule.
• The distinction between true tumor capsule and pseudocapsule can only be made at pathology.
• In at-risk patients, capsule appearance has high positive predictive value for HCC, regardless of whether rim of enhancement represents true tumor capsule or pseudocapsule.
• In observations with diffuse arterial phase hyperenhancement, “capsule” and corona enhancement may overlap in imaging appearance. If rim enhancement increases in portal venous phase or delayed phase, characterize as “capsule”. If rim enhancement occurs in arterial phase and then fades, characterize as corona enhancement.
• Cirrhosis-associated nodules are surrounded by mixed fibrous tissue. The mixed fibrous tissue around these nodules may enhance at imaging and be mistaken for a “capsule”. Characterize as “capsule” only if rim enhancement is unequivocally thicker or more conspicuous than the mixed fibrous tissue surrounding background nodules.

References

• Ishigami K. HCC with a pseudocapsule on gadolinium-enhanced MR images: correlation with histopathologic findings. Radiology 2009
• Khan AS. Value of delayed hypointensity and delayed enhancing rim in MRI diagnosis of small HCC in the cirrhotic liver. J of MRI 2010
• Rimola J. Non-invasive diagnosis of HCC <=2cm in cirrhosis: diagnostic accuracy assessing fat, capsule and signal intensity at dynamic MRI. J Hepatol 2012
• Yu JS. Small hypervsacular HCC: limited value of portal and delayed phases on dynamic MRI. ActaRadiol 2008