Anatomic study of the lymph nodes of the mesorectum

PURPOSE: Lymph node involvement is the most important prognostic factor whe n staging patients with colorectal cancer. The probability of detecting met astasis grows with the number of nodes examined. However, the number of nod es found in surgical specimens varies substantially. We have therefore dete rmined the number and distribution of lymph nodes in the mesorectum by cada veric dissection. METHODS: Twenty formalin-fixed cadaveric pelvises were di ssected (13 males). The search for lymph nodes was performed in a systemati c way, from the division of the superior rectal artery following the smalle st visible branches to the level of the anorectal ring. RESULTS: A total of 168 lymph nodes were found in 20 mesorectal blocks, with a mean (standard deviation) number per specimen of 8.4 (4.45). Lymph node size ranged from 2 to 10 nim. Distribution of lymph nodes in mesorectum was as follows: 120 n odes (71.4 percent) were found around the branches of the superior rectal a rtery proximal to the peritoneal reflection, and 48 nodes (28.6 percent) we re found distal to the peritoneal reflection. Fourteen specimens (70 percen t) had lymph nodes at the division of the superior rectal artery. CONCLUSIO NS: The mean number of lymph nodes found in the mesorectum distal to the su perior rectal artery division was 8.4. Most of these lymph nodes were proxi mal to the peritoneal reflection. The range found in the number of lymph no des per case should be considered for use in the formulation of guidelines in anatomicopathologic studies of surgical specimens obtained after mesorec tal excision.