Definition:

• Intensity in the hepatobiliary phase that unequivocally is less than that of the surrounding liver

Usage

• An observation that is not definitely or probably benign but is hypo-intense in the hepatobiliary phase and iso-intense on all other sequences should be categorized LR ≥ 3. These features should prompt a careful review of all other pre- and postcontrast sequences to identify subtle imaging features that might have been missed initially.
• Ancillary feature that may favor malignancy

If unsure whether an observation in the hepatobiliary phase is hypointense vs. isointense:     

• Characterize as hepatobiliary phase isointense                               

Synonyms:

• Synonyms: hepatobiliary phase hypoenhancement
• Preferred terms: hepatobiliary phase hypointensity
• Rationale for preferred terms:  Feature is descriptive of intensity relative to background liver parenchyma and may not truly represent the ability of the lesion to uptake or retain hepatobiliary contrast agents.

Background:

• Hepatobiliary phase hypointensity is an ancillary feature that favors malignancy and may be used to upgrade an observation (up to but not beyond LR-4).
  • Rationale:  Although hepatobiliary phase hypointensity is characteristic of HCC, it is not specific for HCC. Hepatobiliary phase hypointensity also is seen with hemangiomas, non-HCC malignancies, some dysplastic nodules, siderotic nodules, nodular or confluent fibrosis, some cases of focal fat deposition, and some perfusion alterations.
  • Currently, OPTN does not provide guidance regarding hepatobiliary phase imaging.

Potential pitfalls and challenges: 

• Hepatobiliary phase hypointensity is not equivalent to washout appearance
  • Washout appearance is a major feature used to categorize LR-3, LR-4, and LR-5 observations and should only be assessed during the extracellular phase of contrast (portal venous or delayed phase) prior to significant uptake of hepatobiliary agents  within the hepatocytes