Table 2.

Radiopathological signification of the main imaging features of colorectal liver metastases treated by systemic therapies

Imaging feature	Histological features	Assessment of pathological response to chemotherapy	Limitations/pitfalls
Size modification
Size increase	Viable tumor Acinar central necrosis	No response/progression	Pseudo-progression with immunomodulating agents
Size decrease	Possible remnant viable tumor cell at the periphery Fibrosis deposition Infarct-like necrosis	Partial or major histological responsea	Poor correlation between size decrease and extent of pathological response
Tumor enhancement
Enhancement on delayed phase	Fibrosis deposition	The more fibrosis the better the response	Impossible to differentiate from pre-existing fibrous stroma on imaging Importance of comparing pre and post treatment exams
Central enhancement on hepatobiliary phase	Fibrosis deposition	The more fibrosis the better the response	Impossible to differentiate from pre-existing fibrous stroma on imaging Importance of comparing pre and post treatment exams
Margins
Sharp liver-tumors interface, no enhancement	Absence or limited amount of remnant tumor cells	Major to complete responseb	Only described with CT
Enhancing liver-tumor interfacec	Remnant tumor cells	Absent or minor responseb	The distinction between the two histologic findings is impossible on imaging Importance of comparing pre and post treatment exams
	Dangerous halo (highly proliferating infiltrative tumor cells at the tumor periphery)	Peripheral regrowth after initial response
Tumor content
Calcifications	Mineralization of necrotic tissue	Major response	Tumor regrowth is still possible
Central non-enhancing areas, with high ADC value	Acinar central necrosis	Absent or minor response	The distinction between these histologic findings is impossible on imaging Importance of comparing pre and post treatment exams
	Infarct-like necrosis	Partial or major histological response
	Mucinous subtype	–
	Mucinous regression	Variable histological response

^aHistological response defined according to the Tumor Response Grade [49], with grade 1 or 2: major response, 3: partial response, and 4 or 5: minor response

^bHistological response defined according to Blazer et al. [50], complete response (no residual tumor cells), major response (1% to 49% residual tumor cells), and minor response (≥ 50% residual tumor cells)

^cMay show peripheral hypointensity on diffusion-weighted imaging