Objective Tumor deposits (TDs) are a negative prognostic factor in colorectal cancer, independent of lymph node metastasis (LNM). This study aimed to investigate the ability of pre-operative MRI to identify TDs and differentiate them from LNM in rectal cancer. Materials and methods Patients with histopathological N1-N2 rectal cancer with and without TDs who underwent curative-intent primary surgery between 2013 and 2023 were retrospectively included. Three radiologists independently reviewed pre-operative MR images for the presence of TDs and LNM. Histopathology served as the reference standard from which interobserver agreement by Cohen’s kappa (κ) was calculated. Unblinded node-to-node comparison of MRI and histopathological images was used to identify sources of discrepancies between the modalities. Post hoc analysis stratified on nodal size (> or ≤ 5 mm) was performed. Results Eighty-eight patients (50% with TDs on histopathology, 74% male, median age 70 [20–89] years) were included, of whom 27 were excluded due to poor image quality. Agreement between MRI and histopathology (p), both for TD-presence (κ = −0.04) and LNM-presence (κ = 0.16), was low. In the node-by-node comparison, 43 out of 50 pTDs (86%) measured ≤ 5 mm, and 131 of 167 pLNM (78%) measured ≤ 5 mm. In post hoc analysis of smaller (≤ 5 mm) nodules, no pTDs and 3% of pLNM were diagnosed using MRI. Conclusion MRI demonstrated limited ability in detecting and differentiating TDs and LNM in pre-operative low-risk patients. Diagnostic performance was particularly poor for nodules ≤ 5 mm, which constituted 174 out of 217 (80%) pathological nodular structures. Key Points <Emphasis Type="BoldItalic">Questions</Emphasis> Tumor deposits and lymph node metastasis are important factors for staging rectal cancer, but the ability of pre-operative MRI to detect and differentiate them remains unclear. <Emphasis Type="BoldItalic">Findings</Emphasis> In low-risk rectal cancer patients treated with primary surgery, tumor deposits and lymph node metastasis are often small (≤ 5 mm) and not detected by MRI. <Emphasis Type="BoldItalic">Clinical relevance</Emphasis> MRI has a limited ability to identify and differentiate small (≤ 5 mm) tumor deposits and lymph node metastasis in rectal cancer, which must be considered during pre-operative staging and neoadjuvant treatment planning. Graphical Abstract

Tumor deposits on MRI in rectal cancer—detection and differentiation from lymph nodes with histopathological correlation

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2026年3月18日

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Simon Lundström,
Staffan Täckström,
Peder Wiklund,
Maja Haskå,
Erik Agger,
Lennart Nedar,
Pamela Buchwald

摘要

Objective

Tumor deposits (TDs) are a negative prognostic factor in colorectal cancer, independent of lymph node metastasis (LNM). This study aimed to investigate the ability of pre-operative MRI to identify TDs and differentiate them from LNM in rectal cancer.

Materials and methods

Patients with histopathological N1-N2 rectal cancer with and without TDs who underwent curative-intent primary surgery between 2013 and 2023 were retrospectively included. Three radiologists independently reviewed pre-operative MR images for the presence of TDs and LNM. Histopathology served as the reference standard from which interobserver agreement by Cohen’s kappa (κ) was calculated. Unblinded node-to-node comparison of MRI and histopathological images was used to identify sources of discrepancies between the modalities. Post hoc analysis stratified on nodal size (> or ≤ 5 mm) was performed.

Results

Eighty-eight patients (50% with TDs on histopathology, 74% male, median age 70 [20–89] years) were included, of whom 27 were excluded due to poor image quality. Agreement between MRI and histopathology (p), both for TD-presence (κ = −0.04) and LNM-presence (κ = 0.16), was low. In the node-by-node comparison, 43 out of 50 pTDs (86%) measured ≤ 5 mm, and 131 of 167 pLNM (78%) measured ≤ 5 mm. In post hoc analysis of smaller (≤ 5 mm) nodules, no pTDs and 3% of pLNM were diagnosed using MRI.

Conclusion

MRI demonstrated limited ability in detecting and differentiating TDs and LNM in pre-operative low-risk patients. Diagnostic performance was particularly poor for nodules ≤ 5 mm, which constituted 174 out of 217 (80%) pathological nodular structures.

Key Points

Questions Tumor deposits and lymph node metastasis are important factors for staging rectal cancer, but the ability of pre-operative MRI to detect and differentiate them remains unclear.

Findings In low-risk rectal cancer patients treated with primary surgery, tumor deposits and lymph node metastasis are often small (≤ 5 mm) and not detected by MRI.

Clinical relevance MRI has a limited ability to identify and differentiate small (≤ 5 mm) tumor deposits and lymph node metastasis in rectal cancer, which must be considered during pre-operative staging and neoadjuvant treatment planning.

Graphical Abstract