Methylene blue injection into the rectal artery as a simple method to improve lymph node harvest in rectal cancer

Adequate lymph node assessment in colorectal cancer is crucial for prognosis estimation and further therapy stratification. However, there is still an ongoing debate on required minimum lymph node numbers and the necessity of advanced techniques such as immunohistochemistry or PCR. It has been proven in several studies that lymph node harvest is often inadequate under routine analysis. Lymph nodes smaller than 5mm are especially concerning as they can carry the majority of metastases. These small, but affected lymph nodes may escape detection in routine analysis. Therefore, fat-clearing protocols and sentinel techniques have been developed to improve accuracy of lymph node staging. We describe a novel and simple method of ex vivo methylene blue injection into the superior rectal artery of rectal cancer specimens, which highlights lymph nodes and makes them easy to detect during manual dissection. Initially, this method was developed for proving accuracy of total mesorectal excision. We performed a retrospective study comparing lymph node recovery of 12 methylene blue stained and an equal number of unstained cases. Lymph node recovery differed significantly with average lymph node numbers of 2777 and 1474 (P < 0.001) for the methylene blue and the unstained group, respectively. The largest difference was found in size groups between 1 and 4mm causing a shift in size distribution toward smaller nodes. Metastases were confirmed in 21 and 19 lymph nodes occurring in five and four cases, respectively. Hence, we conclude that methylene blue injection technique improves accuracy of lymph node staging by heightening the lymph node harvest in rectal resections. In our experience, it is a very simple time and cost effective method that can be easily established under routine circumstances.