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Introduction: Lymph node (LN) assessment has a critical role in staging colorectal cancer thus influence 5-year survival rates. Despite this, several studies have shown that the nodal harvest is highly variable and
often inadequate. In this study we retrospectively evaluated the adequacy of LN assessment in our institution and, prospectively, we evaluated if ex-vivo intra-arterial methylene blue dye injection results in a better and more accurate lymph-nodes harvest at standard pathology dissection. We also correlated these with oncologic staging and outcome.
Methods: Inclusion criteria were: elective CRC surgery (R-colectomy, L-colectomy, rectal anterior resection, abdominal perineal excision);no prior colorectal surgery; no preoperative evidence of distant metastatic disease; no previously undetected liver metastasis, advanced disease or carcinosis at surgery. We retrospectively analyzed 146 patients who underwent colorectal cancer resection from 5/2005 to 8/2009 to assess LNs counts (expressed in percentages; <8 or 12 LNs). Prospectively, a total of 204 consecutive patients with primary resectable were studied: after surgery, retrieved specimens were ex-vivo injected (98) or not (106) with methylene blue die and sent for standard pathology. Lymph-nodes were grouped into four categories according to the size: <1mm,1-2mm, 2-4mm and greater than 4mm. Mann-Whitney and Student t-test were used for statistical analysis.
Results: In our retrospective cohort of patients mean number of retrieved LNs was 17+/-7 being <8 LNs in 19% of cases and <12 LNs in 40% with similar percentages among different type of resections.
After blue injection, the average lymph-node harvest was 18+/-6 (range 9-33) in the stained group and 13+/-7 (range 4-34) in the unstained. Despite this trend, the difference was significant only after anterior resection and abdominoperineal excision. Methylene blue injection significantly reduced the risk of inadequate LNs harvest (LNs<8: 17% to 0; LNs <12:30% to 12%). Gender, age (> or < 80 years old), BMI (< or > 28 kgs/m2) and open or laparoscopic surgery did not influence the count. Lower LN counts were observed in both groups after neo-adjuvant radiotherapy.
The largest difference was found in size groups between 1 and 4mm causing a shift in size distribution toward smaller lymph-nodes retrieval.
Conclusions: Ex-vivo intra-arterial methylene blue dye injection augments lymph-nodes retrieval thus allowing a more accurate colorectal cancer staging and possibly the oncologic outcome.