6533b86efe1ef96bd12cbc1c

RESEARCH PRODUCT

Laparoscopic sentinel lymph node mapping and excision of the rectum using a radioactive tracer — a prospective experimental study

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Introduction: Patients with a low risk T1 rectal carcinoma can undergo the therapy of a local excision. In these patients the lymph node status remains unknown. There is a potential risk of up to 7% for nodal metastasis, in high risk cases it can rise up to 35%. To investigate the possibility of using the Sentinel lymph node (SLN) concept, which is anchored in the therapy of malignant melanoma and breast cancer, an experimental study on pigs was undertaken. The objective of the study was to laparoscopically identify and extract SLN’s from the rectum using a radioactive tracer (RT). Material und Methods: The experiment was conducted upon 30 pigs, because sample size calculation indicated that with 30 animals a two sided 95% confidence interval for a single proportion using the large sample normal approximation would extend at most 0,107 from the observed proportion of 0,9. After intubation of the pig 5 trocars were placed for laparoscopy in a semicircular formation on the abdomen. 6–8 cm in proximity of the anus one ml of a mixture of the RT Technetium 99m (Tc99m) and patentblue was administered in the rectum. SLN mapping was conducted 1 hour later, using a laparoscopic Gamma Camera to detect and excise the SLN’s. Then the rectum was excised completely, followed by a search for missed SLN’s. Results: In all operated pigs (n=30) at least 1 SLN (Lymph node with highest measured counts per second (cps)), respectively alltogether 47 SLN’s were identified. The term SLN was assigned for further lymph nodes if the cps Rate was ≥80% of the primary SLN. We detected 1,6 SLN on average (Range 1 to 3 SLN’s). In 27 cases the SLN concept was successful. In one further case the SLN was not immediately identified, because of a cps ≥10000, which was estimated to be the radiation delivered by the nearby located injection site. Sensitivity for detecting SLN’s was 93% (n=30), the probe count rate ranged from 600–10000 cps, with a median of 3800. Conclusion: Minimal invasive mapping and excision of SLN of the rectum using a RT is feasible. The sensitivity for detecting SLN was high (93%). The application of this procedure on humans seems to be possible.