Advanced Lymph Node Staging With Ex Vivo Intra-arterial Indigo Carmine Injection After Transanal Total Mesorectal Excision for Rectal Cancer: A Retrospective Cohort Study

BACKGROUND: Exact lymph node staging is essential in rectal cancer therapy. OBJECTIVE: The aim of the study was to assess the impact of intra-arterial indigo carmine injection after transanal total mesorectal excision on the number of retrieved lymph nodes. DESIGN: This was a retrospective, nonrandomized study. SETTINGS: The study was conducted at a tertiary hospital by a multidisciplinary team. PATIENTS: Patients who underwent transanal total mesorectal excision for suspected rectal cancer between 2013 and 2019 were included. INTERVENTIONS: Rectal cancer specimens received ex vivo intra-arterial indigo carmine injection to stain lymph nodes. MAIN OUTCOME MEASURES: Outcome measures included the number of retrieved lymph nodes with or without staining. RESULTS: Specimens of 189 patients were analyzed, of which 108 (57.1%) were stained with indigo carmine. A mean of 19.8 +/- 6.1 lymph nodes was identified in stained samples compared to 16.0 +/- 4.9 without staining (p < 0.001). Multivariable analysis showed that 3.2 additional lymph nodes were found in stained specimens (95% CI: 1.0 to 5.3; p = 0.02). In stained specimens the adequate lymph node count (>= 12) was increased in univariable (odds ratio: 3.24, 95% CI: 1.13 to 10.65; p = 0.03) but not in multivariable analysis. Indigo carmine injection had no effect on the number of positive lymph nodes or the nodal stage. Chemoradiotherapy reduced the lymph node count by 2.5 (p = 0.008). After staining, 95.0% of patients with chemoradiotherapy had >= 12 lymph nodes retrieved. The median follow-up of patients was 24.2 months with a local recurrence rate of 3.3%. LIMITATIONS: The study is limited by its retrospective design and the nonrandomized allocation. CONCLUSIONS: Ex vivo intra-arterial indigo carmine injection increases the number of isolated lymph nodes after transanal total mesorectal excision regardless of neoadjuvant chemoradiotherapy. Indigo carmine injection is not associated with nodal upstaging or an increased number of tumor-positive lymph nodes.