Iliac (pelvic) lymph nodes

External iliac nodes lie along the external iliac vessels; they receive the efferents of the inguinal nodes (lower limb, abdominal wall below the umbilicus, superficial perineum) and direct lymph from the bladder, prostate, upper vagina, cervix and lower uterine body. Internal iliac nodes follow the branches of the internal iliac artery and drain the pelvic viscera, the deep perineum and the gluteal region; sacral nodes in the hollow of the sacrum drain the posterior pelvic viscera (rectum, prostate, cervix). The obturator nodes, in the obturator fossa, are important sentinel sites for prostate, bladder and cervical cancer. Both external and internal groups drain to the common iliac nodes, which pass lymph to the lumbar (para-aortic) nodes.

The rectum and anal canal illustrate the watershed principle: the upper rectum drains along the superior rectal vessels to the inferior mesenteric nodes, the middle rectum to the internal iliac nodes, and the anal canal below the pectinate line to the superficial inguinal nodes.