The Feasibility of an Ex-vivo Sentinel Lymph Mapping Using Preoperative Radioisotope Injection in Cases of Extraperitoneal Rectal Cancer

Abstract

Purpose: The purpose of this research was to evaluate the feasibility of sentinel lymph node (SLN) mapping involving transanal injection with an ex-vivo mapping in patients with rectal cancer.

Methods: Between April 2007 and December 2009, 20 consecutive patients with T1-3, N0-1 clinical stage rectal cancer preoperatively underwent a SLN procedure using submucosal (99m)Tc-phytate injection. All the patients underwent a total mesorectal excision. After the standard surgical resection, all specimens were identified on lymphoscintigraphy, and bench work was done to pick up the sentinel node basin. All the lymph nodes (non-SLNs and SLNs) were examined using conventional hematoxylin and eosin staining and immunohistochemistry with anti-cytokeratin antibodies.

Results: SLNs were identified from 19 of 20 patients with rectal cancer. The total number of sentinel nodes retrieved from the surgical specimens was 29, and the mean number per patient was 1.6 (range, 0 to 4). In three patients, the SLN was the only positive lymph node. There was one false-negative case with a sensitivity of 88.8% and two upstaged cases (20.0%). The SLN samples from rectal cancer are mainly localized in the pararectal region, but aberrant nodes receive direct drainage from the rectal cancer. On planar lymphoscintigraphy, 15.7% of all patients had aberrant lymphatic drainage to the sigmoid mesenteric or sigmoid lymph node station.

Conclusion: In conclusion, the intraoperative transanal injection for ex-vivo SLN navigation is a safe, feasible surgical modality in patients with rectal cancer. Large studies are warranted to determine the clinical significance of the SLN concept and micrometastasis in rectal cancer.

Keywords: Lymphoscintigraphy; Rectal neoplasms; Sentinel lymph node; Transanal injection.

Fig. 1

Protocol of sentinel node mapping. Intraoperative ^99mTc-phytate was injected into the rectal submucosa. RI, radioisotope; H&E, hematoxylin and eosin staining; IHC, immunohistochemistry.

Fig. 2

Sentinel node navigation on the back table. (A) A gamma-radiation probe-guided sentinel node mapping in patients with rectal cancer. (B) Bench work at a separate back table to pick up each hot node with radioactivity ten times that of background.

Fig. 3

Postoperative images in patient with drainage to perirectal (station 251) and sigmoid (station 241) lymph nodes. Lymphoscintigraphy 5 hours after injection in patient 13 showed tracer uptake in 2 sentinel nodes.

Fig. 4

(A) A micrometastasis (circle) disappears in immunohistochemistry for cytokeratin and carcinoembryonic antigen (CEA) in deeper sections. (B) Isolated tumor cells (arrows) are seen in immunohistochemistry for cytokeratin and CEA, but they are not seen in routine H&E staining.