Improved detection of lymph nodes in cases of rectal cancer using combined methylene blue injection and fat clearance compared with fat clearance alone

Introduction
Evaluation of lymph nodes (LNs) in rectal cancer is a fundamental component of all staging systems. Fat clearance and ex-vivo injection of methylene blue into the inferior mesenteric artery are known methods that can improve LN yield in patients with rectal cancer especially after neoadjuvant chemoradiation. Both techniques were widely compared with routine manual palpation of LNs. The question is that ‘Do adding ex-vivo injection of methylene to fat clearance as a single combined technique give further superiority on fat clearance alone regarding detection of nodal harvest and status?’.
Patients and methods
This study was carried out through comparing clinicopathological data of 40 patients whose specimens were subjected to combined ex-vivo injection of inferior mesenteric artery and xylene fat clearance (group I) with that of 30 patients whose specimens underwent only xylene fat clearance. All patients presented with resectable rectal cancer and have received neoadjuvant chemoradiotherapy.
Results
There was a statistically significant difference regarding total nodal harvest in group I compared with group II (17.52±6.32 vs. 14.56±5.64; <0.05). Similarly, detection of at least 12 LNs was statistically different (87.5 vs. 63.3%; <0.05). However, it was not the case regarding detection of nodal metastases (55 vs. 56.7%), which was not significantly different (=0.085).
Conclusion
Using ex-vivo methylene blue injection into the inferior mesenteric artery and xylene fat clearance as a single combined technique shows a significant difference when compared with xylene fat clearance alone regarding total LN harvest and detection of the optimal number of LNs in cases of rectal cancer. However, it did not show such significance regarding detection of nodal metastases.