Comprehensive Imaging Characterization of Colorectal Liver Metastases

Abstract

Colorectal liver metastases (CRLM) have heterogenous histopathological and immunohistochemical phenotypes, which are associated with variable responses to treatment and outcomes. However, this information is usually only available after resection, and therefore of limited value in treatment planning. Improved techniques for in vivo disease assessment, which can characterise the variable tumour biology, would support further personalization of management strategies. Advanced imaging of CRLM including multiparametric MRI and functional imaging techniques have the potential to provide clinically-actionable phenotypic characterisation. This includes assessment of the tumour-liver interface, internal tumour components and treatment response. Advanced analysis techniques, including radiomics and machine learning now have a growing role in assessment of imaging, providing high-dimensional imaging feature extraction which can be linked to clinical relevant tumour phenotypes, such as a the Consensus Molecular Subtypes (CMS). In this review, we outline how imaging techniques could reproducibly characterize the histopathological features of CRLM, with several matched imaging and histology examples to illustrate these features, and discuss the oncological relevance of these features. Finally, we discuss the future challenges and opportunities of CRLM imaging, with a focus on the potential value of advanced analytics including radiomics and artificial intelligence, to help inform future research in this rapidly moving field.

Keywords: MRI; colorectal (colon) cancer; computed tomography; liver; metastasis; radiomic biomarkers.

Figure 1

Matched imaging and histology of non-encapsulated (A–C) vs capsulated CRLM (A, D, E). Arterial phase gadolinium-enhanced T1 fat saturated MRI of a CRLM with early peripheral enhancement indicating compression of hepatocytes (arrows), (B). Portal venous gadolinium-enhanced T1 fat saturated MRI showing an absence of peripheral enhancement with isointensity to normal liver (arrows), (C). H&E staining (from (A, B) confirming no true capsule with peripheral compression of hepatocytes (arrows). (D). Portal venous phase gadolinium-enhanced T1 fat saturated MRI demonstrating clear peripheral enhancement of a fibrotic capsule (arrows), (E). H&E staining of the CRLM (from (D) confirming a true fibrotic capsule/desmoplastic interface (arrows).

Figure 2

MRI examples of histologically confirmed CRLM with macroscopic vascular invasion. (A, B) Portal venous phase gadolinium-enhanced T1 fat saturated MRI shows CRLM lesions (asterisk) with a filling defect within a hepatic vein indicating macroscopic venous invasion (arrows).

Figure 3

Imaging correlates of internal tumour composition. (A). T2 weighted non-enhanced MRI of a lesion displaying moderately high central T2 signal suggestive of central necrosis (asterisk) and surrounding viable tumour which is higher signal than normal liver (arrows), (B). H&E staining of this CRLM confirms peripheral viable tumour (arrows) with central liquefaction of the metastasis indicating classical Garland necrosis (asterisk), (C). Delayed phase gadolinium-enhanced T1 fat saturated MRI showing avid central delayed enhancement indicating fibrosis (asterisk) with surrounding viable tumour cells which enhance less than normal liver (arrows), (D). H&E staining of this CRLM confirming central fibrosis within the lesion (asteriks) and peripheral viable tumour cells (arrows), (E). T2 weighted sequence demonstrated homogenous high signal mucin (asterisk) (F). H&E staining confirming mucin containing metastasis (asterisk) (G). Delayed phase gadolinium-enhanced T1 fat saturated MRI showing centrally necrotic lesions (no delayed central enhancement, asteriks), (H). Delayed phase Gadolinium enhanced T1 fat saturated MRI showing late central enhancement indicating a centrally fibrotic lesion (asterisk) which contrasts with (G) (central necrosis).

Figure 4

CRLM imaging features following excellent response to Chemotherapy. (A). Portal venous phase gadolinium-enhanced T1 fat saturated MRI showing decreased enhancement relative to liver (arrows), (B). Delayed phase MRI showing increased enhancement relative to liver (arrows), (C). H&E staining of this CRLM confirming almost complete fibrosis of the lesion indicating excellent chemotherapy response. '*' represents the metastasis of interest.

Figure 5

Example of excellent morphological response post-chemotherapy. Both images were obtained using the same MRI scanner performed at 1.5T (GE HDX Twinspeed MR scanner; GE, Milkwaukee, WI) with an 8-channel torso coil. (A) T2 weighted MRI showing a poorly defined CRLM with high T2 region of mucin (asterisk). (B). Following neoadjuvant treatment, this lesion demonstrates no change in size but now has a well-defined margin and replacement of intermediate signal cellular tumour with mucin, indicative of a good morphological response (asterisk). There was a complete pathological response at resection.

Figure 6

Excellent morphological response to chemotherapy. (A). Heterogenously enhancing CRLM on portal venous phase T1-weighted MRI (asterisk). (B), Post-chemotherapy MRI shows the lesion has become homogenous without a reduction in size, indicating a significant decrease in viable tumour cells.