A good understanding of the MRI anatomy of the rectum and its surroundings is pivotal to ensure high-quality diagnostic evaluation and reporting of rectal cancer. With this pictorial review, we aim to provide an image-based overview of key anatomical concepts essential for treatment planning, response evaluation and post-operative assessment. These concepts include the cross-sectional anatomy of the rectal wall in relation to T-staging; differences in staging and treatment between anal and rectal cancer; landmarks used to define the upper and lower boundaries of the rectum; the anatomy of the pelvic floor and anal canal, the mesorectal fascia, peritoneum and peritoneal reflection; and guides to help discern different pelvic lymph node stations on MRI to properly stage regional and non-regional rectal lymph node metastases. Finally, this review will highlight key aspects of post-treatment anatomy, including the assessment of radiation-induced changes and the evaluation of the post-operative pelvis after different surgical resection and reconstruction techniques.

Lymph node status is critical for staging rectal cancer and determining neoadjuvant therapy regimens. Establishing a matching between imaging and histopathological lymph nodes is fundamental for predicting lymph node status. This study reports a technique to achieve node-by-node pairing of mesorectal lymph nodes between imaging findings and histopathology.

Fifty-two patients with histopathologically verified rectal cancer underwent magnetic resonance imaging before surgery. The status of each lymph node in the surgical specimens was analyzed histopathologically and matched with preoperative imaging after the operation.

A total of 346 mesorectal lymph nodes were located on imaging evaluation, of which 313 were confirmed histopathologically, and 33 were unmatched. The total success rate of the technique was 90.5%. Node-by-node analysis revealed 280 benign and 33 malignant nodal structures.

The technique to match mesorectal lymph node imaging findings to histopathology was feasible and effective. It simplified the technical method and had a reasonable success matching rate, which could provide a standardized approach for obtaining a prospective correlation between imaging and histological findings, supporting all subsequent related studies at the level of mesorectal lymph nodes.

To elucidate whether a high level of microsatellite instability (MSI-high) in colon cancer influences the CT assessment of regional lymph node (rLN) morphology and diagnostic performance on predicting pathological node-negative (pN0) patients.

We retrospectively reviewed 507 patients with cecal/proximal ascending colon cancer (age, 63.0 ± 11.6 years; MSI-stable, n = 398; MSI-high, n = 109) who underwent right hemicolectomy between July 1, 2009, and December 31, 2018. Preoperative CT images were assessed for number of rLNs, long/short diameter of the largest rLN, and CT LN grade (CTN0, low probability of metastasis; CTN1, borderline; CTN2, high probability). Sensitivity, specificity, positive predictive value and negative predictive value for predicting pN0 was calculated. Multivariable logistic regression analysis was performed. Statistical significance was defined as P < 0.05.

A study population of 507 patients (mean age ± standard deviation, 63.0 ± 11.6; 264 women) were evaluated. In patients with rLN metastasis, the rLN long axis (pN1: P = 0.013, pN2: P = 0.039) and short axis (pN1: P = 0.001, pN2: P = 0.009) were both longer in MSI-high tumors compared with MSI-stable tumors. High specificity for predicting pN0 was only achieved in MSI-high tumors [sensitivity_MSI-stable = 58.3% (n = 137/235), specificity_MSI-stable = 71.2% (n = 116/163); sensitivity_MSI-high = 38.4% (n = 33/86), specificity_MSI-high = 91.3% (n = 21/23)]. Multivariable logistic regression indicated MSI-high (P < 0.001, odds ratio = 3.701), smaller LN long axis (P = 0.023, odds ratio = 0.905), and lower CT LN grade (CTN0: P = 0.009, odds ratio = 2.987; CTN1: P = 0.014, odds ratio = 2.195) as significant parameters in predicting pN0.

MSI-high colon cancer is associated with larger rLNs and high specificity for predicting pN0 on CT assessment.

Conventional magnetic resonance imaging (MRI) does not accurately evaluate lymph node (LN) status, which is essential for the treatment and prognosis assessment in patients with rectal cancer.

The aim of this study is to evaluate the diagnostic value of intravoxel incoherent motion (IVIM) MRI in differentiating metastatic and nonmetastatic mesorectal LNs with different short-axis diameters in rectal cancer patients.

Forty patients (154 LNs) were divided into three groups based on short-axis diameter: 3 mm ≤ × ≤5 mm, 5 mm < × ≤7 mm, and × >7 mm. MRI characteristics and IVIM parameters were compared between the metastatic and nonmetastatic LNs to determine the diagnostic value for discriminating them.

In the 3 mm ≤ × ≤ 5 mm group, mean D values were significantly lower in metastatic than in the nonmetastatic LNs (P < 0.001). In the 5 mm < × ≤7 mm group, mean f values were significantly lower in metastatic than nonmetastatic LNs (P < 0.05). In the × >7 mm group, only the short-axis diameter of metastatic LNs was significantly greater than that of nonmetastatic LNs (P < 0.05). The area under the curve, sensitivity, specificity, and cutoff values were used for differentiating the metastatic from the nonmetastatic LNs.

IVIM parameters can differentiate metastatic from nonmetastatic LNs with smaller short-axis diameters (× ≤7 mm) in rectal cancer, and the short-axis diameter is a significant factor in identifying metastatic and nonmetastatic LNs in larger short-axis diameter groups (× >7 mm).

For laparoscopic rectal cancer surgery, the inferior mesenteric artery (IMA) can be ligated at its origin from the aorta [high ligation (HL)] or distally to the origin of the left colic artery [low ligation (LL)]. Whether different ligation levels are related to different postoperative complications, operation time, and lymph node yield remains controversial. Therefore, we designed this study to determine the effects of different ligation levels in rectal cancer surgery.

To investigate the operative results following HL and LL of the IMA in rectal cancer patients.

From January 2017 to July 2019, this retrospective cohort study collected information from 462 consecutive rectal cancer patients. According to the ligation level, 235 patients were assigned to the HL group while 227 patients were assigned to the LL group. Data regarding the clinical characteristics, surgical characteristics and complications, pathological outcomes and postoperative recovery were obtained and compared between the two groups. A multivariate logistic regression analysis was performed to evaluate the possible risk factors for anastomotic leakage (AL).

Compared to the HL group, the LL group had a significantly lower AL rate, with 6 (2.8%) cases in the LL group and 24 (11.0%) cases in the HL group (P = 0.001). The HL group also had a higher diverting stoma rate (16.5% vs 7.5%, P = 0.003). A multivariate logistic regression analysis was subsequently performed to adjust for the confounding factors and confirmed that HL (OR = 3.599; 95%CI: 1.374-9.425; P = 0.009), tumor located below the peritoneal reflection (OR = 2.751; 95%CI: 0.772-3.985; P = 0.031) and age (≥ 65 years) (OR = 2.494; 95%CI: 1.080-5.760; P = 0.032) were risk factors for AL. There were no differences in terms of patient demographics, pathological outcomes, lymph nodes harvested, blood loss, hospital stay and urinary function (P > 0.05).

In rectal cancer surgery, LL should be the preferred method, as it has a lower AL and diverting stoma rate.

The imaging of rectal cancer has evolved noticeably over the past 2 decades, paralleling the advances in therapy. The methods for imaging rectal cancer are increasingly used in clinical practice with the purpose of helping to detect, characterize and stage rectal cancer. In this setting, MR imaging emerged as the most useful imaging method for primary staging of rectal cancer; the present review focuses on the role of MR imaging in this regard.

The purpose of this study was to determine if extended PET acquisition times in the pelvis during PET/MRI increase detection rates of potentially metastatic lymph nodes in patients with rectal cancer.

Our study was approved by the institutional review board of the University of California, San Francisco. Twenty-two patients with biopsy-proven rectal cancer underwent imaging via simultaneous 3-T time-of-flight PET/MRI, with seven undergoing two separate PET/MRI examinations, for a total of 29 studies. Each examination included both a whole-body PET/MRI and a dedicated pelvic PET/MRI with both 3- and 15-minute PET acquisitions for the pelvis. Three radiologists interpreted each examination with PET only, MRI only, then combined PET and MRI examinations, using all available images. Additionally, the 3- and 15-minute PET acquisitions of the pelvis were reviewed separately by a single radiologist.

A total of 94 lymph nodes were identified as abnormal on PET, all with MRI anatomic correlates. Of these, 37 (39.4%) were seen only on the dedicated 15-minute acquisition. Fifty-seven (60.6%) nodes measured 5 mm or less, including 29 (30.9%) seen only on the 15-minute acquisition. Thirty-one (33.0%) nodes measured 5.1-10 mm, including eight (25.8%) seen only on the 15-minute acquisition. Of the 17 subjects imaged for initial staging, 11 (64.7%) were upstaged as a result of the increased PET acquisition time (10 from N1 to N2 and one from N0 to N1).

Longer PET acquisition times during PET/MRI for rectal cancer increases the number of FDG-avid lymph nodes detected without increasing scan time.

Modern rectal cancer management is dependent on preoperative staging, and radiological assessment is a crucial part of this process. Imaging must provide sufficient information to guide preoperative decision-making that is reliable and reproducible. Different methods have been used for local staging; however, magnetic resonance imaging (MRI) has shown to be the most reliable tool for this purpose. MRI offers prognostic information about the patients and guides the decision between neoadjuvant treatment and total mesorectal excision alone. Also, not only the initial staging but also restaging by MRI can provide significant information regarding tumor response that is essential when considering alternative approaches.

The decision of ligation at the origin of the inferior mesenteric artery (IMA) or below the origin of the left colic artery (LCA) has remained a dilemma for surgeons in colorectal cancer surgery. The available studies are controversial. The objective of this meta-analysis is to compare the predictive significance of high versus low ligation in colorectal cancer surgery.

A literature search done using Medline, EMBASE, GoogleScholar, and references. A meta-analysis was performed to analyze the 5-year overall survival (OS) of the high and low ligation using hazard ratio (HR) and 95% confidence interval (CI). We further analyzed 2 subgroups considering the level of lymph nodes (LNs) extension. That is IMA positive (+ve) and negative (-ve) LNs. Survival differences were analyzed.

A total of 3119 patients in 5 cohorts were included in this meta-analysis. The pooled HR results showed significant OS benefit of high ligation than low ligation (HR; 0.77, 95% CI: 0.66-0.89) in the "IMA +ve" group with 33% decreased risk, while there is no statistical significance in the "IMA -ve" (HR 0.66, 95% CI: 0.30-1.46) and the "all cases" group (HR 0.69, 95% CI: 0.41-1.15).

The pooled data showed high ligation of IMA has a better survival benefit for the patients with IMA positive LNs. It signifies high ligation should be recommended for the advanced cases or with the suspected high risk of IMA lymphatic metastasis. The limited number of articles demands future high-powered, well-designed randomized controlled trials (RCTs) for the further reliable conclusion.

Simultaneous positron emission tomography and MRI (PET/MRI) is a technology that combines the anatomic and quantitative strengths of MR imaging with physiologic information obtained from PET. PET and computed tomography (PET/CT) performed in a single scanning session is an established technology already in widespread and accepted use worldwide. Given the higher cost and complexity of operating and interpreting the studies obtained on a PET/MRI system, there has been question as to which patients would benefit most from imaging with PET/MRI versus PET/CT. In this article, we compare PET/MRI with PET/CT, detail the applications for which PET/MRI has shown promise and discuss impediments to future adoption. It is our hope that future work will prove the benefit of PET/MRI to specific groups of patients, initially those in which PET/CT and MRI are already performed, leveraging simultaneity and allowing for greater degrees of multiparametric evaluation.

5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2017;46:1247-1262.

We postulated that lymph node (LN) harvest and LN size are influenced by immunologic effects.

To investigate this hypothesis, we performed a retrospective analysis of 170 node-negative colon cancer cases to evaluate the density of intratumoral T lymphocytes (ITLs). CD3- and CD8-positive T cells were counted using a digital system.

The ITL density was significantly increased in cases with sufficient LN harvest and high numbers of LNs larger than 5 mm (LN5). High ITL numbers were associated with improved cancer-specific survival. The analysis of the immune score revealed a significantly different cancer-specific outcome (P = .024), with no cancer-related death in the group with the highest score. The immune score and tumor budding were independently prognostic.

ITL density is independently prognostic and associated with LN harvest and LN size. The immune response is very likely the true explanation for the known prognostic effect of the LN harvest in colon cancer.

The aim of this study was to assess the accuracy of 1.5-T MRI in the pre-operative local T and N staging of colon cancer and identification of extramural vascular invasion (EMVI).

Between 2010 and 2012, 60 patients with adenocarcinoma of the colon were prospectively recruited at 2 centres. 55 patients were included for final analysis. Patients received pre-operative 1.5-T MRI with high-resolution T₂ weighted, gadolinium-enhanced T₁ weighted and diffusion-weighted images. These were blindly assessed by two expert radiologists. Accuracy of the T-stage, N-stage and EMVI assessment was evaluated using post-operative histology as the gold standard.

Results are reported for two readers. Identification of T3 disease demonstrated an accuracy of 71% and 51%, sensitivity of 74% and 42% and specificity of 74% and 83%. Identification of N1 disease demonstrated an accuracy of 57% for both readers, sensitivity of 26% and 35% and specificity of 81% and 74%. Identification of EMVI demonstrated an accuracy of 74% and 69%, sensitivity 63% and 26% and specificity 80% and 91%.

1.5-T MRI achieved a moderate accuracy in the local evaluation of colon cancer, but cannot be recommended to replace CT on the basis of this study.

This study confirms that MRI is a viable alternative to CT for the local assessment of colon cancer, but this study does not reproduce the very high accuracy reported in the only other study to assess the accuracy of MRI in colon cancer staging.

Lymph node size as a prognostic parameter has not been investigated well in the past. Recent data, however, have indicated that this parameter could be even more important than the lymph node count.

Based on the results of earlier studies, we analyzed the lymph node size and number of node-negative colon cancer patients with regard to survival. Data from 115 node-negative cases of colon cancer were analyzed. Lymph nodes with diameters ≤5 mm were defined as small, and all other lymph nodes were classified as intermediate/large in size and labeled LN5. All of the cases were categorized according to the number of LN5s. The LN5 very low (LN5vl) group included cases with less than two LN5s. All of the other cases were assigned to the LN5 low/high (LN5l/h) group.

The overall survival analysis revealed significantly worse outcomes for the LN5vl group, with a mean survival of 34 months compared to the LN5l/h group, with a mean survival of 40 months (P = 0.022). After adjusting for the pT1/2 and pT3/4 stages, we still found a significant outcome difference (P = 0.012). Multivariate analysis identified LN5vl and T-stage as being independently correlated with the outcome. The vast majority of LN5vl cases (91 %) were located in the left colon. The location itself, however, was not prognostic (P = 0.478).

LN5 count, as a marker of immune response, could be shown as being prognostic in node-negative colon cancer. Patients with low LN5 counts showed poor outcomes. These patients could perhaps profit from adjuvant chemotherapy.

The purpose of this article was to outline key technical considerations in performing rectal magnetic resonance imaging (MRI) along with a practical, systematic approach to the interpretation of rectal MRI.

Following validation by the Magnetic Resonance Imaging and Rectal Cancer European Equivalence Study group, rectal MRI is mandatory for the local staging of rectal cancer in many countries. The systematic interpretation of high-quality, high-resolution T2-weighted images should form the basis for discussing the management of patients with rectal cancer, including aiding surgical planning and enabling the appropriate use of neoadjuvant therapy. In this article, we discuss the methods for obtaining high-quality rectal magnetic resonance images and a systematic approach for the accurate interpretation of these images.

Accurate preoperative staging of rectal carcinoma is essential for optimal treatment. This study was designed to evaluate the accuracy and learning curve of endorectal ultrasonography (ERUS) in the preoperative staging of rectal carcinoma. We retrospectively analyzed the records of patients with rectal carcinoma who underwent preoperative ERUS followed by curative surgery at the Shanxi Province Tumor Hospital between January, 2007 and March, 2010. The patients were divided into three groups, namely A, B and C, depending on whether the examination was performed between January and December, 2007, between January and December, 2008 or between January, 2009 and March, 2010, respectively. Five physicians with no prior experience in ERUS performed the examinations. We compared the ERUS staging with the pathological findings using the tumor-node-metastasis (TNM) classification. The accuracy of ERUS in T and N staging after each additional consecutive 20 patients was calculated for physicians D, E and F. A total of 319 patients underwent ERUS prior to surgery. There were 38 patients in group A, 135 in group B and 146 in group C. Two of the five physicians performed only 47 of the 319 examinations, whereas the remaining 272 patients were examined by physicians D (n=162), E (n=64) and F (n=46). The overall accuracy in assessing the extent of rectal wall invasion (T) was 67%, with 16% of the cases overstaged and 17% understaged and the accuracy in assessing nodal involvement (N) was 66%, with 11% of the cases overstaged and 23% understaged. The total T and N staging accuracy of physicians D, E and F was 75 and 72%; 59 and 59%; and 50 and 52%, respectively. For physicians D, E and F, the accuracy of T and N staging after each additional 20 patients was calculated and the curve of the accuracy reached a plateau after physician D completed 80 cases. Therefore, ERUS is a valuable tool for assessing the depth of tumor invasion and it appears that after ~80 cases a physician may be considered able to apply it efficiently.

Early rectal cancer (ERC) is defined as invasive adenocarcinoma spreading into, but not beyond, the submucosa or muscularis propria-that is a Dukes'A: T1N0 or T2N0 tumour in the tumour node metastasis (TNM) classification (Taylor et al. 2008). Among these tumours it is suggested that the most superficial T1 tumours least likely to metastasize to local lymph nodes than adenocarcinoma invading deeper where the rich lymphatic and venous plexuses within the submucosa provide a mechanism for tumour spread beyond the rectum. Currently, only about 10 % of patients presenting symptomatically with rectal cancer are diagnosed with early disease; however, up to 30 % of screen detected cancers are being identified as Dukes'A. Thus, the overall detection of early stage tumours is likely to increase following greater implementation in screening programs. The goal of this invited review is to provide recommendations based on the consensus discussion on the information from preoperative imaging that is of relevance for clinical decision-making for patients with early rectal cancer.

In rectal cancer surgery, it is unclear whether the inferior mesenteric artery (IMA) should be ligated as high as possible, at its origin, or low, below the origin of the left colic artery. We reviewed all relevant articles identified from MEDLINE databases and found that despite a trend of improved survival among patients who underwent high ligation, there is no conclusive evidence to support this. High ligation of the IMA is beneficial in that it allows for en bloc dissection of the node metastases at and around the origin of the IMA, while enabling anastomosis to be performed in the pelvis, without tension, at the time of low anterior resection. High ligation of the IMA does not represent a source of increased anastomotic leak in rectal cancer surgery and postoperative quality of life is improved by preserving the hypogastric nerve without compromising the radicality of the operation. More importantly, high ligation of the IMA improves node harvest, enabling accurate tumor staging. Although the prognosis of patients with node metastases at and around the origin of the IMA is poor, the survival rate of patients with rectal cancer may be improved by performing high ligation of the IMA combined with neoadjuvant and adjuvant therapy.

The purpose of this study was to evaluate the diagnostic accuracy of the pattern of nodal enhancement at MRI enhanced with ultrasmall superparamagnetic iron oxide (USPIO) in the nodal classification of rectal cancer in pathologically matched mesorectal lymph nodes.

Twenty-five patients with adenocarcinoma of the rectum underwent prospective evaluation with 3-mm axial T2-weighted and USPIO-enhanced T2*-weighted MRI before surgery. Mesorectal nodes visible at in vivo MRI were independently scored by two radiologists as malignant or nonmalignant according to morphologic criteria (irregular nodal contour, heterogeneous signal intensity) on T2-weighted MR images and according to USPIO enhancement pattern on T2*-weighted MR images. The sensitivity, specificity, and positive and negative predictive values of morphologic and USPIO criteria in identification of malignancy in the pathologically matched mesorectal nodes were compared by use of the McNemar test. Interobserver agreement was compared by use of kappa statistics.

After surgery, radiologic-pathologic comparison of 126 mesorectal nodes (116 benign, 10 malignant) was possible. Use of morphologic criteria resulted in an average sensitivity of 65% (95% CI, 35-88%); specificity, 75% (67-83%); positive predictive value, 19% (8-34%); and negative predictive value, 96% (91-99%). Use of USPIO criteria resulted in an average sensitivity of 65% (95% CI, 35-88%); specificity, 93% (87-96%); positive predictive value, 43% (21-67%); and negative predictive value, 97% (92-99%). Use of USPIO MRI improved diagnostic specificity for both observers (p < 0.01). Interobserver agreement was fair for morphologic criteria (kappa = 0.39) but good for USPIO criteria (kappa = 0.68).

Use of the pattern of USPIO enhancement had higher diagnostic specificity than but the same sensitivity as morphologic findings in pathologically matched mesorectal lymph nodes.

This study aimed to identify risk factors for local failure in an effort to optimize treatment for rectal cancer.

A total of 154 patients with local failure after abdominal resection were identified from a population-based consecutive series of 2315 patients who underwent operations for rectal cancer in the Stockholm region between January 1995 and December 2004. Surgeons trained in total mesorectal excision performed the surgery, and preoperative radiotherapy was given according to defined protocols. Data from the 9 hospitals in the region, prospectively registered in a database, were reviewed with regard to tumor location and stage, radiation therapy, surgical treatment, and follow-up.

In a multivariable analysis, independent risk factors for local failure were distal tumor location and advanced tumor and nodal stage, omission of preoperative radiation, residual disease, and hospitals with lower caseload. Low anterior resection and total mesorectal excision were deployed more often in centers with low failure rates. Discriminators for radiation therapy were patients with male gender, less advanced age, and tumors situated <6 cm from the anal verge.

The variability of patient outcome according to local failure depends on tumor stage, nodal stage, and location. Omission of radiation therapy and surgical performance are important additional risk factors to consider when optimizing treatment for rectal cancer.

Preoperative chemoradiotherapy has been widely adopted as the standard of care for stage II-III rectal cancers. However, patients with T3N0 lesions had been shown to have a better prognosis than other categories of locally advanced tumor. Thus, neoadjuvant chemoradiation is likely to be overtreatment in this subgroup of patients. Nevertheless, the low accuracy rate of preoperative staging techniques for detection of node-negative tumors does not allow to check this hypothesis. We analyzed a group of patients with cT3N0 low rectal cancer who underwent neoadjuvant chemoradiotherapy with the purpose of evaluating the incidence of metastatic nodes in the resected specimens.

Between January 2002 and February 2008, 100 patients with low rectal cancer underwent clinical staging by means of endorectal ultrasound, computed tomography, positron emission tomography, and magnetic resonance imaging. All patients received preoperative 5-fluorouracil-based chemoradiotherapy and surgical resection with curative aim.

Of 100 patients with locally advanced rectal cancer, 32 were clinically staged as T3N0M0. Pathological analysis showed the presence of lymph node metastases in nine patients (28%) (node-positive group). In the remaining 23 cases, clinical N stage was confirmed at pathology (node-negative group). Node-positive and node-negative groups differ only in the number of ypT3 tumors (P < .01).

Our results indicate that immediate surgery for patients with cT3N0 rectal cancer represents an undertreatment risk in at least 28% of cases, making necessary the use of postoperative chemoradiotherapy. Preoperative chemoradiotherapy should be the therapy of choice on the grounds of the principle that overtreatment is less hazardous than undertreatment for cT3N0 rectal cancers.

Major rectal resection for T1 rectal cancer offers more than 95% cancer specific five-year survival to patients surviving the first 30 days after surgery. A significant further improvement by development of the surgical technique may not be possible. Improvements in the total survival rate have to come from a more differentiated treatment modality, taking patient and procedure related risk factors into account. Subgroups of patients have operative mortality risks of 10% or more. Operative complications and long-term side effects after rectum resection are frequent and often severe.

Local treatment of T1 cancers combined with close follow-up, early salvage surgery or later radical resection of local recurrences or with chemo-radiation may lead to fewer severe complications and comparable, or even better, long-term survival. Accurate preoperative staging and careful selection of patients for local or non-operative treatment are mandatory. As preoperative staging, at present, is not sufficiently accurate, strategies for completion, salvage or rescue surgery is important, and must be accepted by the patient before local treatment for cure is initiated.

It is recommended that polyps with low-risk T1 cancers should be treated with endoscopic snare resection in case of Haggitt's stage 1 or 2. TEM is recommended if resection margins are uncertain after snare resection for Haggitt's stage 3 and 4, and for sessile and flat, low-risk T1 cancers. Average risk patients with high-risk T1 cancers should be offered rectum resection, but old and comorbid patients with high-risk T1 cancers should be treated individually according to objective criteria as age, physical performance as well as patient's preference. All patients treated for cure with local resection or non-surgical methods should be followed closely.

Early rectal cancer (ERC) is adenocarcinoma that has invaded into, but not extended beyond, the submucosa of the rectum (that is a T1 tumour). Local excision is curative for low-risk ERCs but for high-risk cancers such management is controversial.

This review is based on published literature obtained by searching the PubMed and Cochrane databases, and the bibliographies of extracted articles.

ERC presents as a focus of malignancy within an adenoma, as a polyp, or as a small ulcerating adenocarcinoma. Preoperative staging relies on endorectal ultrasonography and magnetic resonance imaging. Pathological staging uses the Haggitt and Kikuchi classifications for adenocarcinoma in pedunculated and sessile polyps respectively. Lymph node metastases increase with the Kikuchi level, with a 1-3 per cent risk for submucosal layer (Sm) 1, 8 per cent for Sm2 and 23 per cent for Sm3 lesions. Low-risk ERCs may be treated endoscopically or by a transanal procedure. Transanal excision or transanal endoscopic microsurgery may be inadequate for high-risk ERCs and adjuvant chemoradiotherapy may be appropriate. There is a low rate of recurrence after local surgery for low-risk ERCs but this increases to up to 29 per cent for high-risk cancers.

Consensus does not exist on the level of arterial ligation in rectal cancer surgery. From oncologic considerations, many surgeons apply high tie arterial ligation (level of inferior mesenteric artery). Other strategies include ligation at the level of the superior rectal artery, just caudally to the origin of the left colic artery (low tie), and ligation at a level without any intraoperative definition of the inferior mesenteric or superior rectal arteries. Publications concerning the level of ligation in rectal cancer surgery were systematically reviewed. Twenty-three articles that evaluated oncologic outcome (n = 14), anastomotic circulation (n = 5), autonomous innervation (n = 5), and tension on the anastomosis/anastomotic leakage (n = 2) matched our selection criteria and were systematically reviewed. There is insufficient evidence to support high tie as the technique of choice. Furthermore, high tie has been proven to decrease perfusion and innervation of the proximal limb. It is concluded that neither the high tie strategy nor the low tie strategy is evidence based and that low tie is anatomically less invasive with respect to circulation and autonomous innervation of the proximal limb of anastomosis. As a consequence, in rectal cancer surgery low tie should be the preferred method.

Rectal cancer is common and nodal disease is an independent adverse prognostic factor for patient survival. Accurate demonstration of the presence and location of nodal disease preoperatively may influence management strategies. In this article we review the pathways of nodal spread in rectal cancer and assessment of nodal disease using sonography, CT, and MRI. The use of morphological criteria instead of size criteria has been shown to improve nodal staging by MRI. The potential role of magnetic resonance lymphography and PET imaging in further improving nodal staging accuracy is discussed.

Accurate preoperative staging of rectal cancer is crucial for therapeutic decision making, as local tumor extent, nodal status, and patterns of metastatic spread are directly associated with different treatment strategies. Recently, treatment approaches have been widely standardized according to large studies and consensus guidelines. Introduced by Heald, total mesorectal excision (TME) is widely accepted as the surgical procedure of choice to remove the rectum together with its enveloping tissues and the mesorectal fascia. Neoadjuvant radiochemotherapy also plays a key role in the treatment of locally advanced stages, while the use of new drugs will lead to a further improvement in oncological outcome. Visualization of the circumferential resection margin is the hallmark of any preoperative imaging and a prerequisite for high-quality TME surgery. The aim of this article is to present an overview on current cross-sectional imaging with emphasis on magnetic resonance imaging. Future perspectives in rectal cancer imaging are addressed.

The aim of this work was to determine the distribution of mesorectal lymph nodes using T2-weighted magnetic resonance (MR) imaging compared with histopathological findings in patients with rectal carcinoma. Sixteen patients with rectal carcinoma undergoing primary surgery without pre-operative neoadjuvant treatment were evaluated using 3-mm axial T2-weighted MR imaging. The position of each visible mesorectal node on imaging was localised by measuring its minimum distance from the mesorectal fascia (d(m)), its minimum distance from the rectal wall (d(r)) and its distance from the distal tumour margin (d(v)). Independent assessment of d(m), d(r) and d(v) was made at histopathological examination. Eighty-five mesorectal nodes on in vivo MR imaging were matched to histopathological findings. On imaging, 67/85 mesorectal nodes were found at the level of the tumour and 84/85 were identified at or within 5 cm proximal to the tumour. Only one out of 85 nodes was seen below the inferior tumour margin. The mean difference of d(m) and d(r) obtained on in vivo MR imaging and histopathological examination was 0.7 mm (95% confidence interval, CI, -0.12 to 1.42 mm) and -1.1 mm (95% CI -2.29 to 0.14 mm), respectively. Almost all mesorectal nodes visible on MR imaging were found at the level of tumour or within 5 cm proximal to the tumour. This has implications for the planning of MR imaging and the level of mesorectal transection at surgery.

To evaluate signal intensity and border characteristics of lymph nodes at high-spatial-resolution magnetic resonance (MR) imaging in patients with rectal cancer and to compare these findings with size in prediction of nodal status.

Forty-two patients who underwent total mesorectal excision of the rectum to determine if they had rectal carcinoma were studied with preoperative thin-section MR imaging. Lymph nodes were harvested from 42 transversely sectioned surgical specimens. The slice of each lymph node was carefully matched with its location on the corresponding MR images. Nodal size, border contour, and signal intensity on MR images were characterized and related to histologic involvement with metastases. Differences in sensitivity and specificity with border or signal intensity were calculated with CIs by using method 10 of Newcombe.

Of the 437 nodes harvested, 102 were too small (<3 mm) to be depicted on MR images, and only two of these contained metastases. In 15 (68%) of 22 patients with nodal metastases, the size of normal or reactive nodes was equal to or greater than that of positive nodes in the same specimen. Fifty-one nodes were above the area imaged, and seven of these contained metastases. The diameter of benign and malignant nodes was similar; therefore, size was a poor predictor of nodal status. If a node was defined as suspicious because of an irregular border or mixed signal intensity, a superior accuracy was obtained and resulted in a sensitivity of 51 (85%) of 60 (95% CI: 74%, 92%) and a specificity of 216 (97%) of 221 (95% CI: 95%, 99%).

Prediction of nodal involvement in rectal cancer with MR imaging is improved by using the border contour and signal intensity characteristics of lymph nodes instead of size criteria.

To evaluate the accuracy of thin-section magnetic resonance (MR) imaging (in-plane resolution, 0.6 x 0.6 mm) in the preoperative assessment of the depth of extramural tumor infiltration, which is a major prognostic indicator in rectal cancer.

In a prospective study of 28 consecutive patients, preoperative MR imaging was performed. The tumor stage according to the TNM classification system and the measured depth of extramural tumor invasion in matched MR images and histopathologic slices were compared.

Preoperative MR imaging correctly indicated the histopathologic tumor stage in all 25 patients in whom comparisons were possible. The difference between the depth of extramural tumor measured on preoperative MR images and corresponding measurements on histopathologic slices of the resection specimen ranged from -5.0 mm to +5.5 mm (mean difference, +0.13 mm; 95% CI: -2.72, +2.98 mm), indicating good agreement. The mesorectal fascia, and the relation of the tumor to it, could be visualized in every case. In all five patients with involvement of the circumferential excision margins of resection specimens, extensive extramural invasion was identified on preoperative MR images.

Preoperative thin-section MR imaging accurately indicates the tumor stage of rectal cancer and depth of extramural tumor infiltration. It provides valuable information for identifying T3 tumors for preoperative adjuvant therapy in patients who are at high risk of failure of complete excision.

The aim of the present study was to investigate whether MRI could predict tumour involvement of the lateral resection margin on resected rectal cancer specimens. 26 specimens obtained after total mesorectal excision were examined in the sagittal and axial plane on a clinical 1.5 T MR system using phased-array surface coils. The shortest distance between the deepest point of tumour penetration and the lateral resection margin was measured. This distance is referred to as LRM. The results were correlated to measurements on digital images of giant histopathological sections. The total number of lymph nodes and lymph node metastases was also counted. LRM was less than or equal to 1 mm (a distance considered for non-radically excised tumours) in eight of the histopathological specimens. On MR images of the resected specimen, LRM was less than or equal to 1 mm in seven of these specimens. LRM was shorter in MR examinations than in histopathological giant sections in 11 specimens. The sensitivity, specificity, positive and negative predictive values for prediction of tumour involvement of the lateral resection margin (LRM < or = 1 mm) by MR of the resected specimen were 88%, 78%, 64% and 93%, respectively. Presence of lymph node metastases could not accurately be predicted by MR. However, it is concluded that the presence of a tumour free lateral resection margin can be predicted by MRI of resected rectal specimens when this exceeds 1 mm.

In surgery for rectal cancer, it is unclear whether the inferior mesenteric artery should be ligated at a high or low position. The study contained herein was undertaken to clarify the indications for high ligation of the inferior mesenteric artery.

Subjects included 198 patients with rectal cancer who underwent resection with high ligation of the inferior mesenteric artery. Nodal metastases were examined by the clearing methods.

The incidence of metastases to the lymph nodes surrounding the origin of the inferior mesenteric artery (root nodes) was 8.6 percent. Inferior mesenteric artery root nodal metastases occurred more frequently with pT3 and pT4 cancer. The five-year survival rate in patients with inferior mesenteric artery root nodal metastases was 38.5 percent; this rate was significantly lower than in those without inferior mesenteric artery root nodal metastases (73.4 percent).

Although the five-year survival rate in patients with inferior mesenteric artery root nodal metastases was lower than in those without metastases, inferior mesenteric artery root nodal dissection should be performed after high ligation of the inferior mesenteric artery for patients with pT3 and pT4 cancers.

The aim of this study was to evaluate the roles of the lymphadenectomy in the surgical treatment of rectal cancer.

On the basis of our experience of 252 curative operations for rectal cancer, we analyze survival and recurrence in relation to the lymph node involvement and to the level of the lymph nodes where the metastases are located. All patients underwent a lymphadenectomy with high ligation of the inferior mesenteric artery and removal of the lumboaortic lymph nodes from the left renal vein to the aortic bifurcation. Pelvic lymphadenectomy was performed in 16 cases.

Five-year survival was 70.6 percent in patients with no lymph node involvement, 68.2 percent in patients with pararectal lymph nodes N+, 25 percent in patients with involvement of intermediate lymph nodes, and 30 percent in patients with involvement of lumboaortic lymph nodes. In no case was there involvement of the hypogastric lymph nodes. On the basis of our experience and from results in the literature, we consider an upward extended lymphadenectomy with high ligation of the inferior mesenteric artery is warranted since it enables the tumor to be staged accurately and may lead to survival even in cases of advanced lymph node involvement.