Location of involved mesorectal and extramesorectal lymph nodes in patients with primary rectal cancer: preoperative assessment with MR imaging

Imaging of Gastrointestinal Tract Ailments

Gastrointestinal (GI) disorders comprise a diverse range of conditions that can significantly reduce the quality of life and can even be life-threatening in serious cases. The development of accurate and rapid detection approaches is of essential importance for early diagnosis and timely management of GI diseases. This review mainly focuses on the imaging of several representative gastrointestinal ailments, such as inflammatory bowel disease, tumors, appendicitis, Meckel's diverticulum, and others. Various imaging modalities commonly used for the gastrointestinal tract, including magnetic resonance imaging (MRI), positron emission tomography (PET) and single photon emission computed tomography (SPECT), and photoacoustic tomography (PAT) and multimodal imaging with mode overlap are summarized. These achievements in single and multimodal imaging provide useful guidance for improved diagnosis, staging, and treatment of the corresponding gastrointestinal diseases. The review evaluates the strengths and weaknesses of different imaging techniques and summarizes the development of imaging techniques used for diagnosing gastrointestinal ailments.

Lymph Nodes Evaluation in Rectal Cancer: Where Do We Stand and Future Perspective

The assessment of nodal involvement in patients with rectal cancer (RC) is fundamental in disease management. Magnetic Resonance Imaging (MRI) is routinely used for local and nodal staging of RC by using morphological criteria. The actual dimensional and morphological criteria for nodal assessment present several limitations in terms of sensitivity and specificity. For these reasons, several different techniques, such as Diffusion Weighted Imaging (DWI), Intravoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), and Dynamic Contrast Enhancement (DCE) in MRI have been introduced but still not fully validated. Positron Emission Tomography (PET)/CT plays a pivotal role in the assessment of LNs; more recently PET/MRI has been introduced. The advantages and limitations of these imaging modalities will be provided in this narrative review. The second part of the review includes experimental techniques, such as iron-oxide particles (SPIO), and dual-energy CT (DECT). Radiomics analysis is an active field of research, and the evidence about LNs in RC will be discussed. The review also discusses the different recommendations between the European and North American guidelines for the evaluation of LNs in RC, from anatomical considerations to structured reporting.

MRI of rectal cancer-relevant anatomy and staging key points

Rectal cancer has the eighth highest cancer incidence worldwide, and it is increasing in young individuals. However, in countries with a high human development index, mortality is decreasing, which may reflect better patient management, imaging being key. We rely on imaging to establish the great majority of clinical tumour features for therapeutic decision-making, namely tumour location, depth of invasion, lymph node involvement, circumferential resection margin status and extramural venous invasion. Despite major improvements in technique resulting in better image quality, and notwithstanding the dissemination of guidelines and examples of standardised reports, rectal cancer staging is still challenging on the day-to-day practice, and we believe there are three reasons. First, the normal posterior pelvic compartment anatomy and variants are not common knowledge to radiologists; second, not all rectal cancers fit in review paper models, namely the very early, the very low and the mucinous; and third, the key clinical tumour features may be tricky to analyse. In this review, we discuss the normal anatomy of the rectum and posterior compartment of the pelvis, systematise all rectal cancer staging key points and elaborate on the particularities of early, low and mucinous tumours. We also include our suggested reporting templates and a discussion of its comparison to the reporting templates provided by ESGAR and SAR.

Understanding the Lymphatics: Review of the N Category in the Updated TNM Staging of Cancers of the Digestive System

OBJECTIVE. The N category has been significantly updated in the 8th edition of the American Joint Committee on Cancer's TNM classification. To ensure correct tumor staging, prognosis, and management, it is critical to be aware of these changes. This article reviews the updated N category, organ-specific regional lymph nodes, and lymphatic drainage pathways for cancers of the digestive system from the esophagus to the anal canal. CONCLUSION. Detection of lymph node involvement may be challenging, and knowledge of nodal characteristics, lymphatic drainage pathways, and imaging modalities is essential to optimize detection rate to ensure accurate staging, prognosis estimation, and streamlined management.

The Impact of Primary Tumor and Locoregional Metastatic Lymph Node SUVmax on Predicting Survival in Patients with Rectal Cancer

Objectives:

The aim of this study was to evaluate the impact of maximum standard uptake value (SUV_max) of the primary tumor and locoregional metastatic lymph node in predicting survival in patients with the preoperative rectal adenocarcinoma.

Methods:

One hundred and fifteen patients [mean age ± standard deviation (SD): 58.7±11.4 years] with biopsy-proven rectal adenocarcinoma underwent ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) imaging for the staging were included in this study. All patients were followed-up for a minimum of 12 months (mean ± SD: 29.7±13.5 months). Tumor-node-metastasis 2017 clinical staging, SUV_max of the primary rectal tumor and locoregional lymph nodes on the PET/CT studies were evaluated.

Results:

All patients had increased FDG activity of the primary tumor. The mean ± SD SUV_max of the primary tumor and locoregional metastatic lymph node were 21.0±9.1 and 4.6±2.8, respectively. Primary tumor SUV_max did not have an effect on predicting survival (p=0.525) however locoregional metastatic lymph node SUV_max had an effect (p<0.05) on predicting survival. Clinical stage of the disease was a factor predicting survival (p<0.001).

Conclusion:

¹⁸F-FDG PET/CT is an effective imaging modality for detecting primary tumors and metastases in rectal adenocarcinoma and clinical stage assessment with PET/CT had an effect on predicting survival. Furthermore, in our study locoregional lymph node SUV_maks was defined as a factor in predicting survival.

Mesorectal radiotherapy for early stage rectal cancer: A novel target volume

With the introduction of population-based bowel cancer screening, rectal cancer is diagnosed at earlier stages, yet standard treatment still requires the same extensive surgery that is used for more advanced stages. Organ preserving treatment is rapidly developing and is subject of investigation in numerous clinical trials. The STAR-TREC trial is an international, multi-centre randomised trial investigating organ preservation using (chemo)radiotherapy. Patients with small mrT1-3bN0V0M0 tumours are randomized between three arms: standard TME, organ preservation with SCRT or with CRT. In this trial, the clinical target volume has been tailored to the early staged disease of the included patients. This mesorectal irradiation volume includes the mesorectum and pre-sacral lymph nodes at the level of the tumour, two centimetres below and cranially up to the S2-3 interspace level. In contrast to conventional irradiation volumes, the lateral lymph nodes and the nodes along the superior rectal artery are excluded. As a result, the dose to the bowel, bladder, anal sphincter and the neurovascular plexus in the lower pelvis is substantially decreased, especially when combined with modern irradiation techniques, such as dynamic arc therapy. These lower doses are expected to lead to decreasing acute and late toxicity and beneficial functional outcomes. The implementation of this novel target volume will be accompanied by an extensive quality assurance program in the STAR-TREC trial. We describe the rationale behind the novel, mesorectal only radiotherapy treatment used in the STAR-TREC trial specifically tailored for early stage disease, with the goal of organ preservation.

Diagnostic and management strategies for lateral pelvic lymph nodes in low rectal cancer-a review of the evidence

Patients with low rectal cancer who have enlarged lateral pelvic lymph nodes are known to have a worse prognosis. There is however uncertainty over what constitutes a lateral pelvic lymph node of clinical significance. As the main modality for the detection of such lymph nodes is magnetic resonance imaging (MRI), characteristics of these lateral lymph nodes identified may have prognostic value and assist with guiding treatment. Options to manage such lateral lymph nodes includes neoadjuvant chemoradiotherapy as well as lateral lymph node dissection. Surgery is extensive and may lead to significant morbidity to the patient. This review article evaluates diagnostic and management strategies in patients with lateral pelvic lymph nodes in low rectal cancer.

Diagnostic performance of 18F-FDG PET/CT using point spread function reconstruction on initial staging of rectal cancer: a comparison study with conventional PET/CT and pelvic MRI

Background

Accurate staging is crucial for treatment selection and prognosis prediction in patients with rectal cancer. Point spread function (PSF) reconstruction can improve spatial resolution and signal-to-noise ratio of PET imaging. The aim of this study was to evaluate the effectiveness of ¹⁸F-FDG PET/CT with PSF reconstruction for initial staging in rectal cancer compared with conventional PET/CT and pelvic MRI.

Methods

A total of 59 patients with rectal cancer underwent preoperative ¹⁸F-FDG PET/CT and pelvic MRI. The maximum standardized uptake value (SUVmax) and lesion to background (L/B) ratio of possible metastatic lymph nodes, and metabolic tumor volumes (MTVs) of primary tumors were calculated. For N and T (T1-2 vs T3-4) staging, sensitivities, specificities, positive predictive values, negative predictive values, and accuracies were compared between conventional PET/CT [reconstructed with ordered subset expectation maximization (OSEM)], PSF-PET/CT (reconstructed with OSEM+PSF), and pelvic MRI. Histopathologic analysis was the reference standard.

Results

For N staging, PSF-PET/CT provided higher sensitivity (78.6%) than conventional PET/CT (64.3%), and pelvic MRI (57.1%), and all techniques showed high specificity (PSF-PET: 95.4%, conventional PET: 96.7%, pelvic MRI: 93.5%). SUVmax and L/B ratio were significantly higher in PSF-PET/CT than conventional-PET/CT (p < 0.001). The accuracy for T staging in PSF-PET/CT (69.4%) was not significantly different to conventional PET/CT (73.5%) and pelvic MRI (73.5%). MTVs of PSF and conventional PET showed a significant difference among T stages (p < 0.001), with higher values in advanced stages. In M staging, both PSF and conventional PET/CT diagnosed all distant metastases correctly.

Conclusions

PSF-PET/CT produced images with higher lesion-to-background contrast than conventional PET/CT, which allowed improved detection of lymph node metastasis without compromising specificity, and showed comparable diagnostic value to MRI in local staging. PSF-PET/CT is likely to have a great value for initial staging in rectal cancer.

Pitfalls in MRI of rectal cancer: What radiologists need to know and avoid

Preoperative staging of rectal cancer using magnetic resonance imaging (MRI) has become an important component of clinical management. Although MRI is the modality of choice for rectal cancer diagnosis and staging, there are certain inherent potential pitfalls that radiologists need to recognize in order to avoid imaging misinterpretation, including choice of MRI protocol; choice of MRI technique; potential mimickers of rectal cancer; mucinous rectal tumor; differentiation between extramural tumor invasion and desmoplastic reaction; differentiation between low rectal cancer and anal cancer; problems relating to nodal involvement, peritoneal reflection, and mesorectal fascia invasion; and, challenges associated with restaging, post-treatment changes, and complications. The aim of this article was to heighten radiologist awareness of these potential pitfalls in order to improve diagnosis, decision-making, and patient outcomes.

Magnetic resonance imaging for diagnosis and neoadjuvant treatment evaluation in locally advanced rectal cancer: A pictorial review

High-resolution pelvic magnetic resonance imaging (MRI) is the primary method for staging rectal cancer. MRI is highly accurate in the primary staging of rectal cancer; however, it has not proven to be effective in re-staging, especially in complete response evaluation after neoadjuvant therapy. Neoadjuvant chemoradiotherapy produces many changes in rectal tumors and on adjacent area, as a result, local tumor extent may not be accurately determined. However, adding diffusion-weighted sequences to the standard approach can improve diagnostic accuracy. In this pictorial review, an overview of the situation of MRI in the staging and re-staging of rectal cancer is exhibited as a pictorial assay. An experience- and literature-based discussion of limitations and difficulties in interpretation are also presented.

Is it time to rethink the rule of total mesorectal excision? A prospective radiological and pathological study in 49 consecutive patients with mid-rectal cancer

AIM

Total mesorectal excision (TME) after neoadjuvant chemoradiotherapy is the standard treatment for T3-T4 and/or N+ mid-rectal tumours, regardless of the exact tumour level. This leads to optimal oncological results but possible impaired functional results. Reducing rectal excision could reduce the functional drawbacks. This study prospectively assessed the risk of N+ or other mesorectal tumour deposit (OTD) below the tumour level by magnetic resonance imaging (MRI) performed after chemoradiotherapy and pathological examination of the TME specimen.

METHOD

Consecutive patients with mid-rectal cancer who underwent TME after chemoradiotherapy were included. A prospective evaluation by postchemoradiotherapy MRI and pathological examination was performed to assess the location of N+ nodes and/or OTDs.

RESULTS

Of 49 consecutive patients, 27 (55%) presented with nodes on postchemoradiotherapy MRI. However, only 12 nodes (size 2-4 mm) in 9 patients (18%) were under the tumour level. On pathological examination, 717 total lymph nodes were found, with 37 N+ and 22 OTD. According to the tumour level: (i) above tumour level, 21/453 nodes were N+ and 6 OTD; (ii) at tumour level, 16/166 nodes were N+ and 15 OTD; (iii) below tumour level, 0/98 nodes (0%) was N+ and only 1 OTD (2%) was noted at 2 cm below tumour level.

CONCLUSION

After chemoradiotherapy, N+ and/or OTD located under the level of the rectal cancer seems to be a very rare event. A postchemoradiotherapy MRI could help detect such patients. For others patients, conservation of the lower rectum with only a subtotal mesorectal excision could possibly improve function.

Good and complete responding locally advanced rectal tumors after chemoradiotherapy: where are the residual positive nodes located on restaging MRI?

PURPOSE

Aim of this study was to evaluate the distribution of persistent mesorectal lymph node metastases on restaging MRI in patients with a good or complete response of their primary tumor (ypT0-2) after CRT for locally advanced rectal cancer.

METHODS

Two hundred and twenty eight locally advanced rectal cancer patients underwent CRT, which resulted in a good response (downstaging to yT0-2) in 144 patients. Forty-nine patients were excluded (no surgery/insufficient follow-up or lacking lesion-by-lesion histology results). This resulted in a final study group of 95 yT0-2 patients. For the patients with a yN(+)-status, a detailed lesion-by-lesion comparison between restaging MRI and histology was performed to evaluate the characteristics and distribution of the individual N(+)-nodes.

RESULTS

7/95 patients (7%) had a yT0-2N(+) status (11/880 (1%) N(+) nodes): no N(+) were found below the tumor level, 55% of the N(+) nodes were located at the level of the tumor, and 45% proximal to the tumor (at a median distance of 1.4 cm above the tumor level). In axial plane, 82% of the nodes were located at the ipsilateral circumference of the tumor, at a median distance of 0.9 cm from the tumor/rectal wall.

CONCLUSIONS

The incidence of persistent metastatic mesorectal nodes after CRT in patients with a good tumor response after CRT is very low. No N(+) nodes are found below the tumor level. All N(+) nodes are located at the level of or proximal to the primary tumor, of which the majority very close to the tumor/lumen.

Correlation of MRI-detected extramural vascular invasion with regional lymph node metastasis in rectal cancer

AIM

To evaluate the value of magnetic resonance imaging-detected extramural vascular invasion (MR-EMVI) in predicting regional lymph node metastasis (RLNM) in patients with rectal cancer.

METHODS

A total of 183 patients were included. A set of clinical and imaging factors including MR-EMVI were evaluated using univariate and multivariate analyses to determine the risk factors for RLNM.

RESULTS

Among the clinical and imaging factors evaluated, MR-EMVI, pathologic EMVI, nodal size, and diffusion-weighted imaging-detected positive nodes were independent predictors of RLNM.

CONCLUSIONS

MR-EMVI may be an independent predictor of RLNM in patients with rectal cancer.

Shifting Paradigms in Minimally Invasive Surgery: Applications of Transanal Natural Orifice Transluminal Endoscopic Surgery in Colorectal Surgery

Since the advent of laparoscopy, minimally invasive techniques such as single port laparoscopy, robotics, endoscopically assisted laparoscopy, and transanal endoscopic surgery continue to revolutionize the field of colorectal surgery. Transanal natural orifice transluminal endoscopic surgery (NOTES) represents a further paradigm shift by combining the advantages of these earlier techniques to reduce the size and number of abdominal incisions and potentially optimize rectal dissection, especially with respect to performance of an oncologically adequate total mesorectal excision (TME) for rectal cancer. Since the first experimental report of transanal rectosigmoid resection in 2007, the potential impact of transanal NOTES in colorectal surgery has been extensively investigated in experimental models and recently transitioned to clinical application. There have been 14 clinical trials of transanal TME (taTME) for rectal cancer that have demonstrated the feasibility and preliminary oncologic safety of this approach in carefully selected patients, with results comparable to outcomes after laparoscopic and open TME, including cumulative intraoperative and postoperative complication rates of 5.5 and 35.5%, respectively, 97.3% rate of complete or near-complete specimens, and 93.6% rate of negative margins. Transanal NOTES has also been safely applied to proctectomy and colectomy for benign indications. The consensus among published series suggests that taTME is most safely performed with transabdominal assistance by surgeons experienced with laparoscopic TME, transanal endoscopic surgery, and sphincter-preserving techniques including intersphincteric resection. Future applications of transanal NOTES may include evolution to a pure endoscopic transanal approach for TME, colectomy, and sentinel lymph node biopsy for rectal cancer, with a potential role for robotic assistance.

MRI in local staging of rectal cancer: an update

Preoperative imaging for staging of rectal cancer has become an important aspect of current approach to rectal cancer management, because it helps to select suitable patients for neoadjuvant chemoradiotherapy and determine the appropriate surgical technique. Imaging modalities such as endoscopic ultrasonography, computed tomography, and magnetic resonance imaging (MRI) play an important role in assessing the depth of tumor penetration, lymph node involvement, mesorectal fascia and anal sphincter invasion, and presence of distant metastatic diseases. Currently, there is no consensus on a preferred imaging technique for preoperative staging of rectal cancer. However, high-resolution phased-array MRI is recommended as a standard imaging modality for preoperative local staging of rectal cancer, with excellent soft tissue contrast, multiplanar capability, and absence of ionizing radiation. This review will mainly focus on the role of MRI in preoperative local staging of rectal cancer and discuss recent advancements in MRI technique such as diffusion-weighted imaging and dynamic contrast-enhanced MRI.

MRI of Rectal Cancer: An Overview and Update on Recent Advances

OBJECTIVE

MRI is the modality of choice for rectal cancer staging. The high soft-tissue contrast of MRI accurately assesses the extramural tumor spread and relation to mesorectal fascia and the sphincter complex. This article reviews the role of MRI in the staging and treatment of rectal cancer. The relevant anatomy, MRI techniques, preoperative staging, post-chemoradiation therapy (CRT) imaging, and tumor recurrence are discussed with special attention to recent advances in knowledge.

CONCLUSION

MRI is the modality of choice for staging rectal cancer to assist surgeons in obtaining negative surgical margins. MRI facilitates the accurate assessment of mesorectal fascia and the sphincter complex for surgical planning. Multiparametric MRI may also help in the prediction and estimation of response to treatment and in the detection of recurrent disease.

Imaging in rectal cancer with emphasis on local staging with MRI

Imaging in rectal cancer has a vital role in staging disease, and in selecting and optimizing treatment planning. High-resolution MRI (HR-MRI) is the recommended method of first choice for local staging of rectal cancer for both primary staging and for restaging after preoperative chemoradiation (CT-RT). HR-MRI helps decide between upfront surgery and preoperative CT-RT. It provides high accuracy for prediction of circumferential resection margin at surgery, T category, and nodal status in that order. MRI also helps assess resectability after preoperative CT-RT and decide between sphincter saving or more radical surgery. Accurate technique is crucial for obtaining high-resolution images in the appropriate planes for correct staging. The phased array external coil has replaced the endorectal coil that is no longer recommended. Non-fat suppressed 2D T2-weighted (T2W) sequences in orthogonal planes to the tumor are sufficient for primary staging. Contrast-enhanced MRI is considered inappropriate for both primary staging and restaging. Diffusion-weighted sequence may be of value in restaging. Multidetector CT cannot replace MRI in local staging, but has an important role for evaluating distant metastases. Positron emission tomography-computed tomography (PET/CT) has a limited role in the initial staging of rectal cancer and is reserved for cases with resectable metastatic disease before contemplating surgery. This article briefly reviews the comprehensive role of imaging in rectal cancer, describes the role of MRI in local staging in detail, discusses the optimal MRI technique, and provides a synoptic report for both primary staging and restaging after CT-RT in routine practice.

Nomogram predicting response after chemoradiotherapy in rectal cancer using sequential PETCT imaging: a multicentric prospective study with external validation

PURPOSE

To develop and externally validate a predictive model for pathologic complete response (pCR) for locally advanced rectal cancer (LARC) based on clinical features and early sequential (18)F-FDG PETCT imaging.

MATERIALS AND METHODS

Prospective data (i.a. THUNDER trial) were used to train (N=112, MAASTRO Clinic) and validate (N=78, Università Cattolica del S. Cuore) the model for pCR (ypT0N0). All patients received long-course chemoradiotherapy (CRT) and surgery. Clinical parameters were age, gender, clinical tumour (cT) stage and clinical nodal (cN) stage. PET parameters were SUVmax, SUVmean, metabolic tumour volume (MTV) and maximal tumour diameter, for which response indices between pre-treatment and intermediate scan were calculated. Using multivariate logistic regression, three probability groups for pCR were defined.

RESULTS

The pCR rates were 21.4% (training) and 23.1% (validation). The selected predictive features for pCR were cT-stage, cN-stage, response index of SUVmean and maximal tumour diameter during treatment. The models' performances (AUC) were 0.78 (training) and 0.70 (validation). The high probability group for pCR resulted in 100% correct predictions for training and 67% for validation. The model is available on the website www.predictcancer.org.

CONCLUSIONS

The developed predictive model for pCR is accurate and externally validated. This model may assist in treatment decisions during CRT to select complete responders for a wait-and-see policy, good responders for extra RT boost and bad responders for additional chemotherapy.

Future directions in surgery for colorectal cancer: the evolving role of transanal endoscopic surgery

SUMMARY 

The morbidity associated with radical surgery for rectal cancer has launched a revolution in increasingly less-invasive methods of resection, including a recent resurgence in transanal endoscopic surgical approaches. The next evolution in transanal surgery for rectal cancer is natural orifice translumenal endoscopic surgery (NOTES). To date, 14 series of transanal NOTES total mesorectal excision (TME) for rectal cancer have been published (n = 76). Overall, the intraoperative and postoperative complication rates of 8 and 28%, respectively, compare favorably to those expected from laparoscopic and open TME. Short-term follow-up after NOTES TME has yielded no cancer recurrence in average-risk patients. High-risk patients have cancer recurrence rates similar to those after laparoscopic TME. Overall, these early data support transanal NOTES TME as a safe and viable alternative to conventional TME. Advances in instrumentation, surgical expertise and neoadjuvant treatment may expand current indications for NOTES even further.

The use of MR imaging in treatment planning for patients with rectal carcinoma: have you checked the "DISTANCE"?

Rectal cancer is a common and serious disease in the Western hemisphere. Optimal treatment of rectal cancer involves a multidisciplinary approach, with collaboration required between radiologists, oncologists, surgeons, and pathologists to achieve local control and decrease the rate of recurrence. Several studies have been published that show the ability to accurately stage rectal cancer with magnetic resonance (MR) imaging. Moreover, advances in preoperative therapies require accurate preoperative staging with MR imaging to select those patients who may benefit from more intensive treatment, without subjecting those who will not benefit to unnecessary treatment. As we enter an era of individualized patient care, stratified according to the risk of both local and distant failure, imaging takes on the same importance as the tumor type and genetic susceptibility. MR imaging is now an essential tool to enable the oncology team to make appropriate treatment decisions. However, rectal cancer evaluation with MR imaging remains a challenge in the hands of nonexperts. This article describes a mnemonic device, "DISTANCE," to enable a systematic approach to the interpretation of MR images, thereby enabling all the clinically relevant features to be adequately assessed: DIS, for Distance from the Inferior part of the tumor to the transitional Skin; T, for T staging; A, for Anal complex; N, for Nodal staging; C, for Circumferential resection margin; and E, for Extramural vascular invasion.

Epithelial-mesenchymal transition biomarkers and support vector machine guided model in preoperatively predicting regional lymph node metastasis for rectal cancer

Background:

Current imaging modalities are inadequate in preoperatively predicting regional lymph node metastasis (RLNM) status in rectal cancer (RC). Here, we designed support vector machine (SVM) model to address this issue by integrating epithelial–mesenchymal-transition (EMT)-related biomarkers along with clinicopathological variables.

Methods:

Using tissue microarrays and immunohistochemistry, the EMT-related biomarkers expression was measured in 193 RC patients. Of which, 74 patients were assigned to the training set to select the robust variables for designing SVM model. The SVM model predictive value was validated in the testing set (119 patients).

Results:

In training set, eight variables, including six EMT-related biomarkers and two clinicopathological variables, were selected to devise SVM model. In testing set, we identified 63 patients with high risk to RLNM and 56 patients with low risk. The sensitivity, specificity and overall accuracy of SVM in predicting RLNM were 68.3%, 81.1% and 72.3%, respectively. Importantly, multivariate logistic regression analysis showed that SVM model was indeed an independent predictor of RLNM status (odds ratio, 11.536; 95% confidence interval, 4.113–32.361; P<0.0001).

Conclusion:

Our SVM-based model displayed moderately strong predictive power in defining the RLNM status in RC patients, providing an important approach to select RLNM high-risk subgroup for neoadjuvant chemoradiotherapy.

Diagnostic accuracy of MRI for assessment of T category, lymph node metastases, and circumferential resection margin involvement in patients with rectal cancer: a systematic review and meta-analysis

BACKGROUND

Magnetic resonance imaging (MRI) is increasingly being used for rectal cancer staging. The purpose of this study was to determine the accuracy of phased array MRI for T category (T1-2 vs. T3-4), lymph node metastases, and circumferential resection margin (CRM) involvement in primary rectal cancer.

METHODS

Medline, Embase, and Cochrane databases were searched using combinations of keywords relating to rectal cancer and MRI. Reference lists of included articles were also searched by hand. Inclusion criteria were: (1) original article published January 2000-March 2011, (2) use of phased array coil MRI, (3) histopathology used as reference standard, and (4) raw data available to create 2×2 contingency tables. Patients who underwent preoperative long-course radiotherapy or chemoradiotherapy were excluded. Two reviewers independently extracted data. Sensitivity, specificity, and diagnostic odds ratio were estimated for each outcome using hierarchical summary receiver-operating characteristics and bivariate random effects modeling.

RESULTS

Twenty-one studies were included in the analysis. There was notable heterogeneity among studies. MRI specificity was significantly higher for CRM involvement [94%, 95% confidence interval (CI) 88-97] than for T category (75%, 95% CI 68-80) and lymph nodes (71%, 95% CI 59-81). There was no significant difference in sensitivity between the three elements as a result of wide overlapping CIs. Diagnostic odds ratio was significantly higher for CRM (56.1, 95% CI 15.3-205.8) than for lymph nodes (8.3, 95% CI 4.6-14.7) but did not differ significantly from T category (20.4, 95% CI 11.1-37.3).

CONCLUSIONS

MRI has good accuracy for both CRM and T category and should be considered for preoperative rectal cancer staging. In contrast, lymph node assessment is poor on MRI.

Lymph node distribution and pattern of metastases in the mesorectum following total mesorectal excision using the modified fat clearing technique

AIM

To define the distribution, size, location and metastasis of lymph nodes (LNs) within the mesorectum from rectal cancer specimens following total mesorectal excision (TME) surgery without neoadjuvant therapy.

METHODS

Specimens from 60 patients who underwent TME were treated with modified fat clearing solution to retrieve LNs. The mesorectum was divided into right lateral, anterior, posterior and left lateral sides, which were further subdivided into three levels (upper, middle and lower).

RESULTS

1436 LNs were harvested, including 985 small LNs (<5 mm in size). The number of LNs from the anterior, posterior and bilateral mesorectum was 125 (8.7%), 696 (48.5%) and 615 (42.8%), respectively. In the longitudinal axis, the difference in distribution at the three levels was not significant. 200 LN metastases (mLNs) were detected in 33 patients. 48% (96/200) of these were small LNs. More mLNs, especially small LNs, were shown in the more advanced T stage patients. The mLN metastasis rate was not influenced by tumour level.

CONCLUSION

Small LN detection increased the accuracy of N staging by 20% in this study. The incidence of metastasis was the same among the anterior, bilateral and posterior areas of the mesorectum. An increased incidence of mLN metastasis in small LNs was associated with more advanced T staging. mLN metastasis rates in both middle and low rectal cancer were higher in the distal mesorectum than that in the proximal mesorectum. LN number and density were not consistent with spread of the primary tumour. Distal mLNs were found in 35% of cases of both middle and distal rectal cancer, implying a need for TME in both.

Clinical significance of magnetic resonance imaging findings in rectal cancer

Staging of rectal cancer is essential to help guide clinicians to decide upon the correct type of surgery and determine whether or not neoadjuvant therapy is indicated. Magnetic resonance imaging (MRI) is currently one of the most accurate modalities on which to base treatment decisions for patients with rectal cancer. MRI can accurately detect the mesorectal fascia, assess the invasion of the mesorectum or surrounding organs and predict the circumferential resection margin. Although nodal disease remains a difficult radiological diagnosis, new lymphographic agents and diffusion weighted imaging may allow identification of metastatic nodes by criteria other then size. In light of this, we have reviewed the literature on the accuracy of specific MRI findings for staging the local extent of primary rectal cancer. The aim of this review is to establish a correlation between MRI findings, prognosis, and available treatment options.

Magnetic resonance imaging (MRI) in rectal cancer: a comprehensive review

Magnetic resonance imaging (MRI) has established itself as the primary method for local staging in patients with rectal cancer. This is due to several factors, most importantly because of the ability to assess the status of circumferential resection margin. There are several newer developments being introduced continuously, such as diffusion-weighted imaging and imaging with 3 T. Assessment of loco-regional lymph nodes has also been investigated extensively using different approaches, but more work needs to be done. Finally, evaluation of tumours during or after preoperative treatment is becoming an everyday reality. All these new aspects prompt a review of the most recent advances and opinions. In this review, a comprehensive overview of the current status of MRI in the loco-regional assessment and management of rectal cancer is presented. The findings on MRI and their accuracy are reviewed based on the most up-to-date evidence. Optimisation of MRI acquisition and relevant regional anatomy are also presented, based on published literature and our own experience.

Diagnostic performance of USPIO-enhanced MRI for lymph-node metastases in different body regions: a meta-analysis

OBJECTIVES

USPIO (ultrasmall superparamagnetic iron oxide contrast agent) MRI was a promising imaging modality in the detection of lymph-node metastases. And this meta-analysis is performed to compare the diagnostic accuracy of USPIO-enhanced MRI with non-enhanced MRI, USPIO-enhanced MRI in various body regions, and postcontrast alone for diagnosis of lymph-node metastases.

METHODS

A comprehensive and systematic search was conducted in PubMed and EMBASE databases. After a systematic review of the studies, sensitivity, specificity, the Q* value and other measures of accuracy of USPIO-enhanced MRI in the diagnosis of lymph-node metastases were summarized. The overall test performance was based on summary receiver operating characteristic curves.

RESULTS

Summary of ROC curve analysis for per-lymph-node data shows a pooled sensitivity of 0.90 (95% confidential interval [CI]: 0.88-0.91) and overall specificity of 0.96 (95% CI: 0.95-0.97) for USPIO-enhanced MRI, the Q* value for USPIO-enhanced MRI is 0.9195, diagnostic odds ratio (DOR) is 162.28 (95% CI: 91.82-286.81). Non-enhanced MRI had less overall sensitivity 0.39 (95% CI: 0.34-0.43) and specificity 0.90 (95% CI: 0.89-0.91), respectively, the Q* value for USPIO-enhanced MRI was 0.6321, DOR is 5.81 (95% CI: 3.64-9.82). Postcontrast MRI alone had sensitivity 0.85 (95% CI: 0.81-0.88) and specificity 0.93 (95% CI: 0.91-0.95), respectively, the Q* value for USPIO-enhanced MRI was 0.8976, DOR is 76.92 (95% CI: 34.21-172.93). There was significant heterogeneity for studies reporting enhanced MRI and non-enhanced MRI.

CONCLUSIONS

This meta-analysis has shown that USPIO-enhanced MRI offers higher diagnostic performance than conventional MRI, and is sensitive and specific for the detection of lymph-node metastases. Postcontrast images alone can equate diagnostic performance pre- and postcontrast MRI has achieved for lymph-node characterization. And the role of USPIO-enhanced MRI in clinical practice still needs to be investigated in future studies.

Extended lymph node dissection for rectal cancer with radiologically diagnosed extramesenteric lymph node metastasis

BACKGROUND

The purpose of this study is to review the clinical outcomes of patients who received extended lymph node dissection for radiologically diagnosed extramesenteric lymph node metastasis.

PATIENTS AND METHODS

The authors reviewed clinical characteristics, short-term operative outcomes, and long-term oncologic outcomes of 151 patients who had received total mesorectal excision plus extended lymph node dissection for the treatment of radiologically diagnosed extramesenteric lymph node metastasis.

RESULTS

The positive predictive value of the radiologic diagnosis of extramesenteric lymph node metastasis was 86.4% for lateral nodes and 40.0% for para-aortic nodes. It showed improvement over time. Perioperative mortality occurred in 3 patients (2.0%) and morbidity in 31 patients (20.5%). Pathologic examinations revealed metastatic para-aortic lymph nodes in 43 patients (PA) and metastatic lateral pelvic nodes in 36 patients (LP), while in 21 patients, metastasis was found in both (LP + PA). Both cancer-specific survival (CSS) and disease-free survival (DFS) were significantly different according to the extent of node metastasis (CSS: P < .001; DFS: P < .001) and univariate and multivariate analyses for prognostic factors revealed that the lymph node status as to location was the only factor.

CONCLUSION

Patients with extramesenteric lymph node metastasis may be a distinct subgroup with poor prognosis. Extended lymph node dissection may have a role for those patients. However, the optimal treatment strategy remains inconclusive, for which further clinical research is necessary.

Magnetic resonance imaging in locoregional staging of rectal adenocarcinoma

A comprehensive overview of the current status of magnetic resonance imaging (MRI) in the locoregional assessment and management of rectal adenocarcinoma is presented. Staging systems for rectal cancer and treatment strategies in its management are discussed to give the reader the context that shapes MRI acquisition techniques and interpretation. Findings on MRI are detailed and their accuracy reviewed based on currently available evidence. Optimization of MRI acquisition and relevant pelvic anatomy are reviewed. A detailed description of our approach in interpreting MRI for locoregional staging of rectal cancer is given and future directions are also introduced.

The number of lymph nodes is correlated with mesorectal morphometry

BACKGROUND

Lymph node involvement is one of the most significant prognostic factors of patients with rectal cancer. However, the distribution of mesorectal lymph nodes is not well known. This study was designed to assess lymph nodes in the mesorectum and to evaluate the correlation between the volume and weight of the mesorectum and the number of lymph nodes.

METHODS

The mesorectums of 20 human cadavers were studied. The volume and weight of the superior rectal mesentery, superior mesorectum and inferior mesorectum were measured. Lymph nodes were sought by manual dissection and were submitted for histological examination. The correlation between the number of lymph nodes and the volume and weight of the mesorectum was evaluated by non-parametric Spearman test.

RESULTS

A total of 178 lymph nodes were identified. The mean number of lymph nodes per specimen was 9.2 +/- 4.5. The lymph nodes were mostly smaller than 3 mm and located in the superior and posterior parts of the mesorectum. A positive correlation was found between the number of mesorectal lymph nodes and the volume and weight of the mesorectum. The number of lymph nodes in the superior rectal mesentery was independent of its volume and its weight.

CONCLUSIONS

Mesorectal lymph nodes are mainly located above the peritoneal reflection within the posterior mesorectum. The positive correlation between the volume or the weight of the mesorectum and the number of mesorectal lymph nodes should be considered as a possible means to determine the minimum number of mesorectal lymph nodes required for histological examination.