The "meso" of the rectum and the "meso" of the pancreas: similar terms but distinct concepts in surgical oncology.

A correspondence between the "meso" of the rectum and of the pancreas has recently been reported. Here we highlight the differences between mesorectum and mesopancreas. Based on anatomical findings from a series of 89 consecutive pancreaticoduodenectomies and 71 consecutive total mesorectal excisions, we observed that in contrast to the mesorectum, the mesopancreas did not have well-defined anatomic boundaries and was continuous and connected through its components with the para-aortic area. In rectal cancer, tumor deposits and nodal involvement could be confined to the mesorectum (i.e., within the mesorectal fascia), whereas in pancreatic carcinoma, tumor deposits and nodal metastases occurred in the boundless mesopancreatic area. Total mesorectal excision was made en bloc with the rectum by dissecting along the mesorectal fascia; this was not the case for mesopancreatic excision since anatomical demarcation of the mesopancreas did not exist. Moreover, the growth pattern of pancreatic cancer showed greater dispersion, which was more prominent at the invasive front of the tumor and could potentially affect the status of the resection margin. These findings indicate that the mesorectum and mesopancreas are completely distinct from the pathological, surgical, and oncological standpoints.