Definition:

• Three-dimensional space-occupying lesion that displaces or replaces underlying hepatic parenchyma

Usage:

• Assessment for mass should be performed on all available imaging sequences/series, particularly those where the vessels are well seen.
• Multiplanar images (source or reformatted) may help in the characterization of observations as masses or not masses by showing to better advantage some of the features below
• Imaging features that, if present, favor mass include:
  • Displacement of vessels
  • Bulging or retraction of liver surface
  • Architectural distortion
  • Rounded shape
  • Capsule appearance

• Imaging features that, if present, favor non-mass include:
  • Undistorted vessels traversing observation
  • Absence of mass effect
  • Preservation of hepatic architecture
  • Geographic shape

If unsure about feature:

• Characterize as mass if observation may represent infiltrative HCC or infiltrative other malignancy (LR-M).
• Otherwise, do not characterize as mass

Synonyms:

• Synonyms: masslike, mass-like, nodule
• Preferred terms: mass

Background:

• Assessment for mass is used to distinguish observations that may represent malignancy and require further characterization from those observations that may represent atypical benign entities such as perfusional alterations
• Examples of mass:
  • Expansile mass
  • Infiltrative mass
  • Mass that invades vein (i.e., tumor in vein), even if parenchymal component of mass is not identified at imaging

Potential pitfalls and challenges

• Masses may overlap in imaging appearance with observations that are not masses (e.g., rounded perfusion alterations, hypertrophic pseudomass, hepatic fat deposition/sparing)
  • Masses will typically cause displacement, compression, or invasion of vessels.  Perfusion alterations, hypertrophic pseudomass, and hepatic fat deposition/sparing do not distort the vessels and the vessels typically pass through the observation.