Morphology of the mesorectum in patients with primary rectal cancer.

PURPOSE: The size and contents of the pelvis differ between the genders, and this may affect mesorectal size and shape. The aim of this prospective pilot study was to examine radiologically the applied anatomy of the mesorectum. METHODS: Fifty-eight patients (35 male, 23 female) with primary rectal cancer who had suitable high-resolution staging pelvic magnetic resonance images between November 2002 and July 2004 were studied. Ten variables of mesorectal morphology were measured on axial images at the ischial spines. The associations between morphologic variables and gender and body mass index were examined. RESULTS: Compared with female patients, male patients had a larger area of overall mesorectal package (3,776 mm(2) vs. 2,772 mm(2), P = 0.001), larger area of mesorectal fat (2,562mm(2) vs. 1,842mm(2), P = 0.001), and higher ratio of anteroposterior to transverse diameter of the mesorectal package (0.82 vs. 0.56, P < 0.001). The anterior mesorectal fat buffer was significantly thinner in females than in males (2.9 mm vs. 7.8 mm, P < 0.001). Mesorectal fat area was greater in males with a body mass index > 25 than with a body mass index < 25. CONCLUSIONS: Males have a larger overall mesorectal package compared with females, mainly caused by mesorectal fat. The anterior mesorectal fat is significantly thinner in females than in males. Such morphologic differences may affect resection margin status.