ACR LI-RADS

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Definition:

Imaging appearance of a “capsule” around a mass when no true tumor capsule is present at histological evaluation.

Comments:

Attributed to compressed parenchyma, fibrosis (i.e., mixed fibrous tissue or septal fibrosis similar to that surrounding cirrhotic nodules), or dilated sinusoids/blood vessels around mass, or a combination of the above.
A rim of increasing enhancement in the portal venous phase or delayed phase around a mass at imaging is termed capsule appearance (synonym: portal venous/delayed phase peripheral rim enhancement). It may represent a true tumor capsule or a pseudocapsule. Imaging does not reliably differentiate between a true tumor capsule and a pseudocapsule.
In high-risk patients, capsule appearance has high positive predictive value for HCC, regardless of whether rim of enhancement represents a true tumor capsule or a pseudocapsule.
The distinction between pseudocapsule and true tumor capsule can only be confirmed on pathology

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