Advanced Lymph Node Staging with Ex Vivo Intraarterial 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 intraarterial indigo carmine injection after transanal total mesorectal excision on the number of retrieved lymph nodes. DESIGN Retrospective, non-randomized 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. INTERVENTIONS Rectal cancer specimen received ex vivo intraarterial indigo carmine injection to stain lymph nodes. MAIN OUTCOME MEASURES 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% confidence interval: 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% confidence interval: 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 non-randomized 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 increased number of tumor positive lymph nodes. See Video Abstract at http://links.lww.com/DCR/B839.