Size and distribution of lymph nodes in rectal cancer resection specimens.

Abstract

The detection of lymph node involvement is fundamental to the staging of rectal cancer, and aids in prognostication and identification of patients who will benefit from adjuvant therapy. The anatomical variation in distribution and size of mesorectal lymph nodes has received scant attention. This study aimed to determine the size and distribution of lymph nodes in rectal cancer resection specimens. This was a prospective, observational study of rectal cancer resection specimens analyzed by a single histopathologist. This study was conducted from January 2007 to July 2013 at the authors' institution. Two hundred forty-four consecutive patients underwent resection for rectal cancer. The size and distribution of lymph nodes in the resection specimens and the anatomical position of mesorectal lymph nodes in relation to the peritoneal reflection, tumor, and anal verge were recorded. A total of 10,473 lymph nodes were retrieved in 244 patients (75 women; median age, 68 years (interquartile range, 59-75 years)). One hundred seventy-three anterior resection and 71 abdominoperineal resection specimens were analyzed. Median lymph node yield was 41 lymph nodes (interquartile range, 31-52); 344 of 10,473 (3.2%) lymph nodes were positive. Lymph nodes were distributed in the mesorectum, sigmoid mesentery, and vascular pedicle in 40%, 32%, and 28% of the patients. Sixty-eight percent of mesorectal lymph nodes were above the peritoneal reflection. Mesorectal lymph node distribution in relation to the tumor was 53% above, 36% adjacent to, and only 11% below the tumor. Ninety-five of 334 (28%) positive nodes were ≤3 mm in diameter. Resection specimens analyzed by other pathologists (<5%) have not been included, and fat clearance techniques were not used to retrieve lymph nodes. To ensure accurate nodal staging of rectal cancer, both resection and subsequent pathological evaluation should focus on the mesorectum in close proximity to the tumor and along the superior rectal artery. Small lymph nodes (<3 mm in size) should not be overlooked, and lymph node metastasis to the sigmoid mesentery is rare (see Video, Supplemental Digital Content 1, http://links.lww.com/DCR/A177).