Post-TACE assessment of hepatocellular carcinoma

Post-TACE assessment of hepatocellular carcinomas is essential for evaluating the success of the therapy. 

Hepatocellular carcinomas that are not amenable to definitive therapy with thermal ablation or resection can be treated with trans-arterial chemoembolization (TACE). The end goal may be palliation or downstaging to meet liver transplantation criteria, depending on the situation.

The imaging follow up schedule varies between institutions, but a 1 month follow up exam with follow up exams every three months afterward has been adopted by some centers. The short interval follow up studies allow quick retreatment in case there is recurrent tumor or development of new tumor.

Radiographic features

Post-TACE evaluation is typically performed with MRI or contrast-enhanced CT. The MRI features are described here, but the CT features are analogous.

On the initial (1 month) follow up the treated lesion may be unchanged in size (or perhaps slightly increased in size), but on future evaluations the lesion should decrease in size.

CT

Immediate post treatment CT is usually requested to assess the deposition of the radio-opaque ethiodized oil used in the procedure. Since the oil delivers the chemotherapeutic agent, deposition of oil in the lesion correlates with a good treatment effect. This hyperatteunating oil hinders evaluation for enhancement, however.

DEB-TACE (drug-eluting beads) does not use the same ethiodized oil delivery system, and the beads are not radio-opaque, so this procedure is not typically followed up with CT.

MRI

• T1
  • ​​variable signal intensity due to hemorrhage and liquefactive necrosis
  • hemorrhagic debris often has increased T1 signal
• T2
  • variable signal intensity due to hemorrhage and liquefactive necrosis
• DWI/ADC
  • useful as an adjunct evaluation of the treatment zone in equivocal cases
    • residual or recurrent tumor may present as hyperintensity on DWI and corresponding hypointensity on the ADC sequence
• T1 C+ (Gd)
  • successfully treated tumor should be nonenhancing
    • a thin rim of inflammatory hyperenhancement is common, but it should not be thickened, irregular, or masslike
      • this thin rim of enhancement may persist for up to 12 months (and occasionally beyond)
    • geographic hyperenhancement in the treated area is common, but is a result of the treatment
      • it should not "wash out" on the portal venous phase 
      • this enhancement does not typically persist on sequential follow up exams
  • subtraction images may be useful for identifying enhancing areas within T1 hyperintense hemorrhagic debris

Hepatobiliary-specific contrast agent is not typically used for post-TACE assessment.

Radiology report

In the LI-RADS system, treated lesions fall into three categories for treatment response (TR) ¹:

• LR-TR nonviable: expected post-treatment chance with no arterial phase enhancement or other finding to suggest residual or recurrent tumor
• LR-TR equivocal
• LR-TR viable: nodular or masslike enhancement in the treatment zone with arterial phase hyperenhancement, wash out on the portal venous phase, or enhancement similar to the pre-treatment lesion

The long dimension and orthogonal measurement of the enhancing component of the ablation zone are also reported (the whole zone is not necessarily measured):

• longest dimension (mRECIST)
• orthogonal (bidimensional) measurements (EASL)