Incidence of extramural venous invasion in colorectal carcinoma: findings with a new technique.

In reported studies of extramural venous invasion (EVI) by colorectal carcinoma (CRC) in which conventional preparations involving a sectioning plane perpendicular to the tumor were used, an incidence as high as 36% has been found for unselected surgical material from patients operated on for cure. However, with this preparation technique, not all of the veins that exit the bowel wall roughly at right angles can be examined adequately. We investigated whether preparation of the adjacent vascular connective tissue with tangential sectioning might not result in different EVI rates. A total of 100 unselected surgical specimens of the bowel bearing 103 CRCs were prepared using a previously undescribed method, and EVI was found in 54.1% of the cases considered to have been treated curatively. To assess EVI fully, a complete study of all the vessels draining the tumor would be required yet the conventional preparation technique is associated with the distinct possibility of sampling error, because only a few vessels in each block are sectioned in the longitudinal axis. This sampling error might well be the explanation for the considerably higher incidence of EVI in our cases than in the reports in the literature. In all patients with EVI, the possibility of hematogenous metastases exists, and this has a significant bearing on the question of selecting patients for adjuvant chemotherapy.