Definition:

• A discrete border of hypointensity surrounding an observation in the hepatobiliary phase.

Usage

• Considered a subset or type of distinctive rim, an ancillary feature that favors malignancy
• Applies to a hypointense rim seen on the hepatobiliary phase, thought to represent a tumor capsule and can be seen with HCC as an ancillary feature that favors malignancy.  
  • Hypointense rim specifically favors HCC as opposed to malignancy in general.
  • This feature may be used to upgrade an observation (up to but not beyond LR-4).

If unsure about feature:

• Do not characterize as feature.

Synonyms:

• Synonyms: hepatobiliary phase rim, hepatobiliary phase capsule

• Preferred term:  Hepatobiliary phase hypointense rim
• Rationale:  Descriptive term that draws distinction from the capsule appearance seen on portal venous phase or delayed phase.

Potential pitfalls and challenges

• ICC may show peripheral hypointensity in the hepatobiliary phase, corresponding to peripheral tumor cellularity, which may be mistaken for a hypointense rim of HCC. This peripheral cellular tumor tissue characteristically shows a peripheral washout appearance in the late dynamic phase and, as it is not composed of hepatocytes, appears hypointense in the hepatobiliary phase.  The center of the tumor appears hyperintense relative to the periphery due to retention of contrast material within its fibrous matrix. When an observation shows peripheral hypointensity in the hepatobiliary phase, differentiation between the hypointense rim of HCC and the peripheral hypointensity of ICC may be difficult, and evaluation of additional imaging features may be required for diagnosis.  In some cases biopsy may be necessary.