The Avocado Sign: A novel imaging marker for nodal staging in rectal cancer.

Objectives: To evaluate the diagnostic performance of the Avocado Sign, a novel contrast-enhancement-based MR imaging marker, for prognostication of mesorectal lymph node spread in rectal cancer.

Methods: This retrospective study included 106 patients with rectal cancer who underwent MRI examination. The Avocado Sign, defined as a hypointense core within an otherwise homogeneously hyperintense lymph node on contrast-enhanced T1-weighted images, was assessed. Of the cohort, 77 patients received neoadjuvant chemoradiotherapy followed by restaging MRI. Histopathological examination served as the reference standard. Diagnostic metrics were calculated and compared between subgroups using chi-square tests. Interobserver agreement was evaluated using Cohen's kappa.

Results: The Avocado Sign demonstrated high diagnostic accuracy for predicting lymph node involvement, with an overall sensitivity of 88.7%, specificity of 84.9%, PPV of 85.5%, NPV of 88.2%, and accuracy of 86.8%. The area under the ROC curve was 0.87. Subgroup analysis revealed excellent performance in both patients undergoing surgery alone (sensitivity 100%, specificity 83.3%) and those receiving neoadjuvant therapy (sensitivity 84.2%, specificity 85.4%). Interobserver agreement was almost perfect (κ = 0.92).

Conclusion: The Avocado Sign is a promising imaging predictor for mesorectal lymph node status in rectal cancer. Its straightforward application, high reproducibility, and remarkable diagnostic accuracy underline its potential to refine MRI staging. However, further validation in larger, prospective multicenter studies is warranted to confirm these findings and assess their impact on clinical decision-making.

Key points: Question Can the Avocado Sign on contrast-enhanced MRI improve mesorectal lymph node staging in rectal cancer independently of classical morphological criteria? Findings The Avocado Sign demonstrated high sensitivity (88.7%) and specificity (84.9%) as a standalone marker for predicting mesorectal lymph node involvement. Clinical relevance Incorporating contrast-enhanced sequences and the Avocado Sign into MRI protocols enhances nodal staging accuracy in rectal cancer, potentially informing treatment decisions. Further validation is required to confirm its effectiveness and compare it with existing criteria.