Rectum lymphatic draining system is rather complex and is performed in 3 directions:
1. ascending down the higher haemorrhoidal-inferi-or mesenteric arterial peduncle to the para-aortal lymph nodes;
2. lateral down the middle haemorrhoidal artery to the iliac and obturator lymph nodes;
3. descending down the lower haemorrhoidal artery to the inguinal lymph nodes.
The direction of the lymphatic flow depends on the rectal site, the ascending way representing a lymphatic discharge common to the whole rectum, and the lateral way constituting an almost exclusive draining of the lower rectum and of the anal canal above the pectinate line [2,17]. According to Heald and Moran  and Stelzner , the main metastatic spreadway starts from the mesorectum with an ascending polar ity, whereas a caudal and lateral dissemination would represent a rather rare event (1-2%), always secondary to the retrograde lymphatic spread in the case of very advanced neoplasias [8,10]. Some lymphoscinti-graphic studies highlight the lymphatic flow as almost exclusively down the higher haemorrhoidal lymphatics-inferior mesenterics, and do not show any connection between the internal iliac lymph nodes and the inferior mesenterics [19,20].
Arnaud et al.  remark, however, on a pattern of lateral lymphatic draining to the internal iliac lymph nodes in 50% of control cases using the same method.
In the 1920s Villemin et al.  in France and Senba  in Japan, in anatomy and post mortem studies showed the existence of lateral lymphatics, starting from the lower rectum (beneath the Houston middle valve), spreading around the internal iliac arteries and inside the obturator regions as well.
In 1951, Sauer and Bacon , while performing a pre-operative injection consisting of a colouring substance in the lower rectum mucosa, confirmed the presence of a lymphatic flow down the middle rectal vessels, inside the lateral ligaments, emphasising the opportunity to perform a lymphadenectomy extended to the lateral ligaments and to the iliac vessels to control the lymphatic spread of lower rectal cancer [9,24].
If the historical evaluations pointed out a neoplastic lateral spread in the 0-9% range , more recent and detailed pathologic studies show that such an event occurs in 23-41.8% of patients having rectal cancer below the peritoneal reflection [3,17, 25].
Lateral metastasis is usually associated with the presence of pararectal positive lymph nodes, and it represents an isolated event in about 5% of cases . Pelvic nodes that are more frequently involved are the ones down the middle rectal artery (11%), the obturator pelvic nodes (8.9%) and internal iliac pelvic nodes (6.4%) .
The remark that rectal cancer has a relatively slow locoregional progression and anatomy and clinical data suggesting the existence of a primary and precocious relay to lateral lymph nodes (at least regarding the low rectum) , give a theoretical explanation for the adoption of more extended lymphadenec-tomies [2,14, 17, 24].
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