Lymph Nodes Evaluation in Rectal Cancer: Where Do We Stand and Future Perspective

Abstract

The assessment of nodal involvement in patients with rectal cancer (RC) is fundamental in disease management. Magnetic Resonance Imaging (MRI) is routinely used for local and nodal staging of RC by using morphological criteria. The actual dimensional and morphological criteria for nodal assessment present several limitations in terms of sensitivity and specificity. For these reasons, several different techniques, such as Diffusion Weighted Imaging (DWI), Intravoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), and Dynamic Contrast Enhancement (DCE) in MRI have been introduced but still not fully validated. Positron Emission Tomography (PET)/CT plays a pivotal role in the assessment of LNs; more recently PET/MRI has been introduced. The advantages and limitations of these imaging modalities will be provided in this narrative review. The second part of the review includes experimental techniques, such as iron-oxide particles (SPIO), and dual-energy CT (DECT). Radiomics analysis is an active field of research, and the evidence about LNs in RC will be discussed. The review also discusses the different recommendations between the European and North American guidelines for the evaluation of LNs in RC, from anatomical considerations to structured reporting.

Keywords: diffusion-weighted imaging; magnetic resonance imaging; nodal staging; rectal cancer.

Figure 1

Man 53 y.o. with mucinous rectal cancer. Tumor deposit (arrow), assessed in T2W sequence (A), in b 50 s/mm² (B), in b 800 s/mm² (C) and ADC map (D).

Figure 2

Woman 65 y.o. with rectal cancer. Tumor deposit (arrow) assessed in T2W sequence (A), in b 800 s/mm² (B), in ADC map (C), in Dt map (D), in Dp map (E) and Fp map (F).

Figure 3

Man 72 y.o. with rectal cancer. Nodal assessment (arrow) in T2W sequence (A), in b 800 s/mm² (B), in ADC map (C), in Dt map (D), in Dp map (E) and Fp map (F).

Figure 4

Woman 65 y.o. with rectal cancer (same patient as in Figure 2). Tumor deposit (arrow) assessed in T2W sequence (A), in MK map (B) and MD map (C).

Figure 5

Man 72 y.o. with rectal cancer (same patient as in Figure 3). Nodal assessment (arrow) in T2W sequence (A), in MK map (B) and MD map (C).

Figure 6

Woman 65 y.o. with rectal cancer (same patient of Figure 2 and Figure 4). DCE- MRI (A) deposit assessment with Intensity/Time curve evaluation (B).

Figure 7

Man 72 y.o. with rectal cancer (same patient as in Figure 3 and Figure 5). DCE- MRI (A) nodal assessment with Intensity/Time curve evaluation (B).