Significance of mesorectal volume in staging of rectal cancer with magnetic resonance imaging and the assessment of involvement of the mesorectal fascia.

The aim was to study the influence of mesorectal volume, as estimated by magnetic resonance imaging (MRI), that is to be removed during total mesorectal excision (TME), on the accuracy of the first preoperative MRI of rectal cancer compared to histopathology, and its correlation to locoregional prognostic factors. A total of 267 rectal cancer patients from a multinational study (MERCURY or MRI equivalence study) had their mesorectal volume retrospectively estimated by researchers without knowledge of the assessments made by the radiologist or the pathologist. The evaluations made by the pathologist and the radiologist were then compared, including T- and N-staging, assessment of extent of extramural tumor invasion (the largest portion of the tumor beyond the muscularis propria or EMI) and distance to mesorectal fascia; the discrepancies in the results were correlated to the mesorectal volume. T- or N-staging accuracy by MRI and the difference between the EMI as measured by the pathologist and the radiologist were not dependent on individual mesorectal volume. There was no correlation between assessment of involvement of mesorectal fascia or local neighboring organs by MRI and histopathology with mesorectal volume. Mesorectal volume does not affect locoregional prognostic factors or the accuracy of local staging of rectal cancer.