Abdominal Radiology (2019) 44:3527–3535 https://doi.org/10.1007/s00261-019-02094-0 SPECIAL SECTION: RECTAL CANCER Nodal drainage pathways in primary rectal cancer: anatomy of regional and distant nodal spread Harmeet Kaur1 · Randy D. Ernst1 · Gaiane M. Rauch1 · Mukesh Harisinghani2 Published online: 18 October 2019 © Springer Science+Business Media, LLC, part of Springer Nature 2019 Abstract Nodal involvement is a signifcant prognostic factor in rectal cancer and difcult to assess preoperatively. An understanding of the patterns of nodal spread from diferent regions of the rectum can assist in this process and is essential for the purposes of surgical planning. In this article we defne patterns of spread to mesenteric and pelvic sidewall nodal subgroups and discuss the importance of accurate anatomic localization of nodes for the purposes of staging and surgical planning. Keywords Rectal cancer · Rectal adenocarcinoma · Lymph node · MRI · CT Introduction The anatomic defnition of the rectum specifes its supe- rior or upper extent as the point of coalescence of the taenia Lymph node spread is an important prognostic factor in rec- to form a continuous outer longitudinal muscle layer in the tal cancer. An understanding of lymphatic drainage path- rectum. Inferiorly the anatomic rectum ends at the dentate ways from diferent regions of the rectum, the most common line, which also is the point of transition between columnar nodal groups’ involved and accurate localization of these epithelium lining the rectum and the squamous epithelium nodes to mesenteric, pelvic sidewall and retroperitoneal lining the anatomic anal canal, which extends down from the compartments is important in the accurate staging and sur- dentate line to the anal verge [1]. gical planning of rectal cancer. In contrast the current convention in the radiology lit- The rectum has a dual blood supply: from the mesenteric erature places the inferior end of the rectum at the level of vessels i.e., the inferior mesenteric and superior rectal ves- the anal verge, incorporating the anatomic anal canal into sels and from pelvic sidewall vessels i.e., branches of the the lower rectum. The superior end of the rectum is placed internal iliac artery including the middle and inferior rectal 15 cm above the anal verge. arteries. Lymphatic drainage from the rectum for the most There are various defnitions of the rectum put forward by part follows the course of these arteries. diferent surgical societies; the Japanese society for cancers of the colon and rectum defnes the rectum as extending Defnitions of the rectum and pathways from the sacral promontory to the upper edge of the pubo- of lymphatic drainage rectalis muscle, a defnition that moderately aligns with the anatomic boundaries of the rectum. While, the American There are numerous defnitions of the rectum: anatomical, society of colon and rectal surgeons classifes any tumor surgical, and radiological. whose distal margin is 15 cm or less from the anal verge as a rectal cancer [2, 3]. The subdivisions of the rectum also vary, but the most * Harmeet Kaur commonly used approach by both radiologists and surgeons [email protected] in the United States is to divide the rectum into three sec- 1 Department of Diagnostic Imaging, University of Texas MD tions from the anal verge, the lower rectum (0–5 cm), middle Anderson Cancer Center, 1400 Pressler Street, Unit 1473, (5–10 cm), and upper (10–15 cm). Houston, TX 77030, USA The limitation of this approach is that it does not refect 2 Division of Abdominal Imaging, Department of Radiology, the pathways of lymphatic drainage of the rectum which is a Massachusetts General Hospital, Harvard Medical School, 55 key determinant of nodal involvement. From the perspective Fruit Street, Boston, MA 02114, USA Vol.:(0123456789)1 3 3528 Abdominal Radiology (2019) 44:3527–3535 of patterns of lymphatic drainage, the peritoneal refection A third lymphatic drainage zone is located inferior to is an important landmark. The peritoneal refection can also the dentate line or the anatomic anal canal. Tumors located be localized to approximately the level of the middle rectal below this point drain upward along the mesenteric lymphat- valve of Houston or 6-9 cm above the anal verge. In addition ics but also laterally to superfcial inguinal nodes which are the peritoneal refection itself can also be easily identifed on defned on cross sectional images as nodes caudal to the a signifcant percentage of rectal MRI scans [4, 5]. inguinal ligament. Rectal tumors located above the peritoneal refection drain almost exclusively along nodes following the mesen- Nodal anatomy teric vessels, and include the pararectal/mesorectal nodes, the superior rectal and fnally the inferior mesenteric nodes. As previously mentioned pathways of lymphatic drainage A refection of this almost exclusive upward pathway of lym- for the rectum can be broadly compartmentalized to two phatic drainage in high rectal tumors is the low incidence separate regions, the mesenteric nodes and extra mesenteric of pelvic sidewall nodal involvement in tumors above the which include pelvic sidewall and retroperitoneal nodes. peritoneal refection which in surgical studies was found to Since lymphatic drainage pathways follow the rectal blood be 1.5–3.6%. This incidence is seen to increase to about 21% supply, most commonly the arteries, the names of the nodes in tumors that were located at the level of the peritoneal refect the adjacent vessel and the sub-classifcation of these refection. In contrast tumors located below the peritoneal nodes refects the relationship of the node relative to the refection also drain upwards along the mesenteric vessels, vessel. but have signifcant drainage laterally towards pelvic side- wall nodes. This is refected in the 41.8% incidence of meta- static pelvic sidewall nodes seen in rectal tumors below the Mesenteric nodes peritoneal refection. It is to be noted, however, that pelvic sidewall nodes even in low rectal tumors are seen primarily This drainage pathway refers to nodes located in the meso- in T3–T4 tumors and are rare in early stage rectal tumors rectum and the mesentery of the sigmoid colon; and includes [6, 7] (Fig. 1). pararectal nodes also called mesorectal nodes, superior Fig. 1 Lymphatic drainage from the entire rectum and anal canal is upward (dotted light green arrow) along mesenteric ves- sels. Mesenteric nodes can be classifed as the principal IMA node at origin of the IMA from aorta, IMA nodes seen along IMA to level of the left colic artery and superior rectal nodes. Lymphatic drainage from below the peritoneal refection (dotted blue line) also extends laterally to pelvic sidewall nodes. These nodes are located primarily along the obturator and internal iliac vessels 1 3 Abdominal Radiology (2019) 44:3527–3535 3529 rectal nodes, inferior mesenteric artery nodes, and principal Pelvic sidewall nodes inferior mesenteric artery (IMA) node [8]. The principal IMA node refers to the node at the point The overall incidence of pelvic sidewall involvement in all of origin of the inferior mesenteric artery from the aorta. rectal tumors is 8.8–23% [6, 7, 9]. However, as previously While all the remaining nodes along the inferior mesenteric mentioned, pelvic sidewall nodal involvement is uncommon artery to the point of origin of the left colic artery are cat- in rectal tumors located above the peritoneal refection, but egorized simply as IMA nodes (Figs. 1 and 2). This repre- can be seen in tumors at and below the peritoneal refection sents the most common pathway of nodal spread in rectal [6]. cancer. When metastatic nodes are present in rectal cancer, The pelvic sidewall nodal groups are classifed and named the overwhelming majority involves the mesenteric compart- according to the adjacent vessel as common iliac, external ment, and of these involved nodes most are located in the iliac, and internal iliac/hypogastric nodes and can be further mesorectum [6, 9]. classifed into subgroups. Fig. 2 a The principal IMA node (arrowhead) is identifed adjacent to the inferior mesenteric artery (arrow) close to the origin of artery from the aorta. b and c Superior rectal nodes are seen along the course of the superior rectal vessels in the axial and coronal planes (arrows) 1 3 3530 Abdominal Radiology (2019) 44:3527–3535 External iliac nodes are subdivided into lateral, mid- along the obturator internus exiting the pelvis at the obtu- dle and medial chains. The lateral subgroup as the name rator foramen (Fig. 3a and b) [10]. suggests are located lateral to the external iliac artery, the The lateral and middle chain external iliac nodes are middle between the artery and vein, and medial posterior almost never involved in rectal cancer. These nodal groups to the external iliac vein. The nodes in the medial sub- have their main aferent lymphatics from the lower limb. In group are in close proximity to nodes along the obturator a study by Moriya et al. of 149 Duke C tumors arising below vessels and are the subject of some controversy as they the peritoneal refection, no external iliac nodal metastasis are frequently indistinguishable from obturator nodes that were found [11]. Consequently, although enlarged oblong are seen along the course of the obturator artery as it runs nodes are frequently observed in these locations on cross from its origin from the internal iliac/hypogastric artery sectional imaging, based on patterns of lymphatic spread in rectal cancer these nodes are unlikely to be involved even Fig. 3 External iliac nodal subgroups: a Lateral (arrowheads), middle to the obturator artery (small white arrow) and medial to the obtura- (small arrow on left) external iliac nodes receive aferent lymphatic tor internus muscle (arrowhead). c and d Enlarged oblong nodes are supply from the lower extremity and are rarely involved in rectal can- commonly seen in the middle (small arrow) and lateral subgroups cer.