Accuracy of staging rectal tumors with contrast-enhanced transrectal MR imaging

Contemporary management of rectal cancer

The management of rectal cancer has undergone significant changes over the past 50 years, and this has been associated with major improvements in overall outcomes and quality of life. From standardization of total mesorectal excision to refinements in radiation delivery and shifting of chemoradiotherapy treatment to favor a neoadjuvant approach, as well as the development of targeted chemotherapeutics, these management strategies have continually aimed to achieve locoregional and systemic control while limiting adverse effects and enhance overall survival. This article highlights evolving aspects of rectal cancer therapy including improved staging modalities, total neoadjuvant therapy, the role of short-course and more selective radiotherapy strategies, as well as organ preservation. We also discuss the evolving role of minimally invasive surgery and comment on lateral pelvic lymph node dissection.

Key message

Rectal cancer management is constantly evolving through refinements in radiation timing and delivery, modification of chemoradiotherapy treatment schedules, and increasing utilization of minimally invasive surgical techniques and organ preservation strategies. This manuscript aims to provide a synopsis of recent changes in the management of rectal cancer, highlighting contemporary modifications in neoadjuvant approaches and surgical management to enhance the knowledge of surgeons who care for this challenging population.

MRI-based parameters and clinical risk factors to predict lymph node metastasis in patients with ypT0 rectal cancer after neoadjuvant chemoradiotherapy

BACKGROUNDS

The aim of this study was to assess the significant risk factors that predict lymph node metastasis in ypT0 patients with locally advanced rectal cancer following chemoradiotherapy (CRT). Additionally, the study aimed to identify high-risk groups who would not be suitable candidates for a rectal-preserving strategy, despite achieving a complete tumour response.

METHODS

Between 2013 and 2021, 226 ypT0 patients with stages II/III rectal cancer underwent CRT and radical surgery were enrolled. Two groups of patients were evaluated: those with lymph nodes metastasis and those without. The selection of variables for multivariable logistic regression was conducted through bivariate logistic regression analysis. Furthermore, the determination of optimal cutoff values for risk factors was achieved using ROC curve analysis.

RESULTS

Nearly 8% (18/226) of patients with ypT0 had positive lymph nodes (LN) on final pathology. Four variables resulted as being independent factors of LN metastasis: pre-CRT tumour movability (OR = 8.618, P = 0.003), pre-CRT maximal LN size (OR = 28.474, P = 0.004), post-CRT tumour vertical length (OR = 1.492, P = 0.050), post-CRT anaemia (OR = 10.288, P = 0.001). The optimal cutoff point of pre-CRT maximal LN size and post-CRT tumour vertical length was 7.50 mm and 3.05 cm, respectively.

CONCLUSION

The prevalence of lymph node metastasis remains at 8% among patients who achieve pathological complete regression of the primary tumour. In instances where patients are considered appropriate candidates for a rectal-preserving strategy after clinical complete remission, careful consideration should be given to the selection of this strategy if specific risk factors are present. These risk factors encompass a maximal LN size surpassing 7.50 mm prior to CRT, a fixed tumour prior to CRT, a tumour vertical length exceeding 3.05 cm after CRT, and the existence of anaemia subsequent to CRT.

Intra- and Interobserver Variability in Magnetic Resonance Imaging Measurements in Rectal Cancer Patients

Colorectal cancer is the second most common cancer in Europe, and accurate lymph node staging in rectal cancer patients is essential for the selection of their treatment. MRI lymph node staging is complex, and few studies have been published regarding its reproducibility. This study assesses the inter- and intraobserver variability in lymph node size, apparent diffusion coefficient (ADC) measurements, and morphological characterization among inexperienced and experienced radiologists. Four radiologists with different levels of experience in MRI rectal cancer staging analyzed 36 MRI scans of 36 patients with rectal adenocarcinoma. Inter- and intraobserver variation was calculated using interclass correlation coefficients and Cohens-kappa statistics, respectively. Inter- and intraobserver agreement for the length and width measurements was good to excellent, and for that of ADC it was fair to good. Interobserver agreement for the assessment of irregular border was moderate, heterogeneous signal was fair, round shape was fair to moderate, and extramesorectal lymph node location was moderate to almost perfect. Intraobserver agreement for the assessment of irregular border was fair to substantial, heterogeneous signal was fair to moderate, round shape was fair to moderate, and extramesorectal lymph node location was substantial to almost perfect. Our data indicate that subjective variables such as morphological characteristics are less reproducible than numerical variables, regardless of the level of experience of the observers.

Poor response at restaging MRI and high incomplete resection rates of locally advanced mucinous rectal cancer after chemoradiation therapy

AIM

Mucinous carcinoma is a histological subtype of rectal cancer and has been associated with a poor response to neoadjuvant chemoradiotherapy (CRT). The primary aim of this study was to analyse the response on MRI of mucinous locally advanced rectal cancer (LARC) after CRT compared to regular adenocarcinoma.

METHOD

Patients with LARC (defined as cT4 and/or cN2), who underwent CRT followed by restaging MRI and surgery in two tertiary referral hospitals were retrospectively included in the study. Pre- and post-treatment MRI was reviewed by an experienced abdominal radiologist.

RESULTS

A total of 102 patients, of whom 29 were diagnosed with mucinous carcinoma, were included for analysis. At restaging MRI, adenocarcinoma patients demonstrated significantly less clinical involvement of the mesorectal fascia (37% vs. 62%, P = 0.003) while this was not demonstrated in mucinous carcinoma patients (86% vs. 97%, P = 0.16). Significant downstaging after CRT in adenocarcinoma patients (P = 0.01) was seen while, in mucinous carcinoma patients, no downstaging after CRT (P = 0.89) was seen. Pathology revealed significantly higher rates of an involved circumferential resection margin in mucinous carcinoma versus adenocarcinoma patients (27.6% vs. 1.4%; P < 0.001). After multivariate regression analysis, mucinous carcinoma remained an independent prognostic factor for local recurrence (hazard ratio 3.6; 95% CI 1.1-12.4), although no differences in overall or disease-free survival were observed.

CONCLUSION

Mucinous rectal carcinoma is associated with a poor clinical response at restaging MRI after CRT, leading to relatively higher rates of involved circumferential resection margins at pathology. In this cohort, mucinous carcinoma seems to be a prognostic factor for increased risk of local recurrence, without an effect on overall survival.

Magnetic Resonance Imaging Evaluation of the Accuracy of Various Lymph Node Staging Criteria in Rectal Cancer: A Systematic Review and Meta-Analysis

Background

Magnetic resonance imaging (MRI)-based lymph node staging remains a significant challenge in the treatment of rectal cancer. Pretreatment evaluation of lymph node metastasis guides the formulation of treatment plans. This systematic review aimed to evaluate the diagnostic performance of MRI in lymph node staging using various morphological criteria.

Methods

A systematic search of the EMBASE, Medline, and Cochrane databases was performed. Original articles published between 2000 and January 2021 that used MRI for lymph node staging in rectal cancer were eligible. The included studies were assessed using the QUADAS-2 tool. A bivariate random-effects model was used to conduct a meta-analysis of diagnostic test accuracy.

Results

Thirty-seven studies were eligible for this meta-analysis. The pooled sensitivity, specificity, and diagnostic odds ratio of preoperative MRI for the lymph node stage were 0.73 (95% confidence interval [CI], 0.68–0.77), 0.74 (95% CI, 0.68–0.80), and 7.85 (95% CI, 5.78–10.66), respectively. Criteria for positive mesorectal lymph node metastasis included (A) a short-axis diameter of 5 mm, (B) morphological standard, including an irregular border and mixed-signal intensity within the lymph node, (C) a short-axis diameter of 5 mm with the morphological standard, (D) a short-axis diameter of 8 mm with the morphological standard, and (E) a short-axis diameter of 10 mm with the morphological standard. The pooled sensitivity/specificity for these criteria were 75%/64%, 81%/67%, 74%/79%, 72%/66%, and 62%/91%, respectively. There was no significant difference among the criteria in sensitivity/specificity. The area under the receiver operating characteristic (ROC) curve values of the fitted summary ROC indicated a diagnostic accuracy rate of 0.75–0.81.

Conclusion

MRI scans have minimal accuracy as a reference index for pretreatment staging of various lymph node staging criteria in rectal cancer. Multiple types of evidence should be used in clinical decision-making.

The utility of preoperative radiological evaluation of early rectal neoplasia: a systematic review and meta-analysis

AIM

The diagnostic role for preoperative imaging of clinically benign rectal adenomas is unclear. The objective of this systematic review and meta-analysis was to examine the diagnostic accuracy of preoperative imaging in distinguishing benign adenomas from rectal cancer.

METHOD

A systematic search was performed for all studies published that correlated staging of clinically benign rectal adenomas with endorectal ultrasound (ERUS) or MRI and histology. Imaging was compared with postoperative histology and data on the numbers of true positives, false positives, true negatives and false negatives were extracted. Summary estimates of sensitivity and specificity with 95% CIs were calculated using a bivariate random effects model. The QUADAS2 tool was used to determine the methodological quality of included studies.

RESULTS

Eleven studies describing 1511 patients were retrieved. A total of 1134 patients underwent local excision and 377 had a formal proctectomy. A benign rectal adenoma was diagnosed in 840 and 214 had a T1 rectal cancer. For confirming benign adenomas, the pooled sensitivity of ERUS was 0.81 (95% CI 0.69-0.89) and specificity was 0.85 (95% CI 0.68-0.93). For detecting occult T1 tumours, the pooled sensitivity of ERUS was 0.50 (95% CI 0.33-0.66) and specificity was 0.89 (95% CI 0.82-0.94). Quantitative analysis of MRI could not be performed due to insufficient studies.

CONCLUSION

This study demonstrates the limited accuracy of preoperative ERUS in distinguishing benign adenomas from T1 rectal cancer. Preoperative imaging must be interpreted with caution to prevent over-staging and unnecessary proctectomy. We propose that clinically benign lesions may undergo local excision, with subsequent management based on final histology.

Rectal Cancer: Staging

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.

Lymph node metastasis in rectal cancer: comparison of MDCT and MR imaging for diagnostic accuracy

PURPOSE

To compare the diagnostic accuracies of MDCT and high-resolution MRI (HR-MRI) for regional nodal metastases with different short-axis diameter ranges in rectal cancer patients.

METHODS

Rectal adenocarcinoma patients who underwent both MDCT and HR-MRI before surgery were included. The maximum short-axis diameters of the nodes were measured, and were classified as benign or malignant on imaging findings. All of the nodes were subdivided as follows: ≤ 5 mm (Group A), > 5 mm and ≤ 10 mm (Group B) , and > 10 mm (Group C). The postoperative pathological reports were used as the standard, and the sensitivity, specificity, accuracy, ROC curve, and AUC value were calculated for each subgroup.

RESULTS

A total of 592 nodes were included in the node-to-node evaluation. In Group A, the specificity and accuracy of HR-MRI were significantly higher than those of MDCT (99.28% vs. 93.99%, P < 0.001; 95.78% vs. 89.56%, P = 0.010; respectively). In Group B, the specificity and accuracy of HR-MRI were also higher than those of MDCT (98.36% vs. 55.74%, P < 0.001; 80.45% vs. 66.17%, P < 0.001; respectively). For Groups A and B, the AUCs of MDCT were both 0.65, whereas those of HR-MRI were 0.76 and 0.82, respectively. In Group C, all nine malignant nodes were correctly diagnosed metastases on MDCT, whereas one was misjudged as benign on HR-MRI.

CONCLUSIONS

The diagnostic value of HR-MRI is superior to that of MDCT, with higher specificity, accuracy, and AUC values for HR-MRI than for MDCT.

Assessment of remaining tumour involved lymph nodes with MRI in patients with complete luminal response after neoadjuvant treatment of rectal cancer

OBJECTIVE

To assess the accuracy of MRI to predict remaining lymph node metastases in patients with complete pathological luminal response (ypT0) after neoadjuvant therapy.

METHODS

Data from a national registry were used. 19 patients with histopathologically remaining lymph node metastases (ypT0N+) were identified. Another 19 patients without lymph node metastases (ypT0N0) were used as matched controls. Two radiologists blinded to all patient information evaluated staging and restaging MRI that was compared to histopathological findings of the resected specimen.

RESULTS

The average size of the largest lymph node on restaging MRI was significantly larger (4.5 mm) in the ypT0N+ group than in the ypT0N0 group (2.6 mm) (p = 0.04). Presence of ypN+ was correctly predicted by MRI in 7 of 19 patients. In patients without lymph node metastases (ypT0N0), these were correctly classified by MRI in 16 of 19 patients. All patients who had MR-identified lymph nodes larger than 8 mm at restaging were ypTN+. The sensitivity, specificity, positive predictive value and negative for prediction of remaining lymph node metastasis with MRI were 37, 84, 70 and 57%.

CONCLUSION

In patients with ypT0 in rectal cancer after neoadjuvant treatment, remaining regional lymph node metastases cannot safely be predicted by restaging MRI alone using presently known criteria. Presence of a lymph node over 8 mm on restaging MRI strongly indicates yPN+. Advances in knowledge: This is one of the first studies on MRI lymph node assessment after chemo-radiotherapy (CRT) in luminal complete response.

Gadolinium-Based Contrast Agent During Pelvic MRI: Contribution to Patient Management in Rectal Cancer

BACKGROUND

Few publications exist regarding gadolinium-enhanced sequences in rectal MRI. None have evaluated its potential impact on patient management.

OBJECTIVE

This study aimed to assess whether gadolinium-enhanced sequences, including dynamic contrast enhancement, change radiologic interpretation and clinical management of rectal cancer.

DESIGN

This is a retrospective analysis of 100 rectal MRIs (50 baseline and 50 postneoadjuvant treatment), both without and with gadolinium-enhanced sequences. Treatment plans were rendered based on each radiologic interpretation for each case by a single experienced surgeon. Differences in radiologic interpretation and management were statistically analyzed.

SETTINGS

The study was conducted at the Memorial Sloan Kettering Cancer Center.

PATIENTS

Patients undergoing rectal MRI between 2011 and 2015 for baseline tumor staging and/or postneoadjuvant restaging were included.

MAIN OUTCOME MEASURES

Primary outcome measures were changes in radiologic tumor stage, tumor margins, and surgical planning with the use of gadolinium at baseline and postneoadjuvant time points.

RESULTS

At baseline, tumor downstaging occurred in 8 (16%) of 50 and upstaging in 4 (8%) of 50 with gadolinium. Postneoadjuvant treatment, upstaging occurred in 1 (2%) of 50 from T2 to T3a. At baseline, mean distances from tumor to anorectal ring, anal verge, and mesorectal fascia were not statistically different with gadolinium. However, in 7 patients, differences could have resulted in treatment changes, accounted for by changes in relationships to anterior peritoneal reflection (n = 4), anorectal ring (n = 2), or anal verge (n = 1). Postneoadjuvant treatment, distances to anorectal ring and anal verge (in centimeters) were statistically smaller with gadolinium (p = 0.0017 and p = 0.0151) but could not have resulted in clinically significant treatment changes.

LIMITATIONS

This study was limited by its retrospective design.

CONCLUSIONS

The use of gadolinium at baseline MRI could have altered treatment in 24% of patients because of differences in tumor stage or position. Postneoadjuvant treatment, gadolinium resulted in statistically smaller distances to sphincters, which could influence surgical decision for sphincter-preserving rectal resection. See Video Abstract at http://links.lww.com/DCR/A444.

Gadolinium-Based Contrast Agent During Pelvic MRI: Contribution to Patient Management in Rectal Cancer

BACKGROUND

Few publications exist regarding gadolinium-enhanced sequences in rectal MRI. None have evaluated its potential impact on patient management.

OBJECTIVE

This study aimed to assess whether gadolinium-enhanced sequences, including dynamic contrast enhancement, change radiologic interpretation and clinical management of rectal cancer.

DESIGN

This is a retrospective analysis of 100 rectal MRIs (50 baseline and 50 postneoadjuvant treatment), both without and with gadolinium-enhanced sequences. Treatment plans were rendered based on each radiologic interpretation for each case by a single experienced surgeon. Differences in radiologic interpretation and management were statistically analyzed.

SETTINGS

The study was conducted at the Memorial Sloan Kettering Cancer Center.

PATIENTS

Patients undergoing rectal MRI between 2011 and 2015 for baseline tumor staging and/or postneoadjuvant restaging were included.

MAIN OUTCOME MEASURES

Primary outcome measures were changes in radiologic tumor stage, tumor margins, and surgical planning with the use of gadolinium at baseline and postneoadjuvant time points.

RESULTS

At baseline, tumor downstaging occurred in 8 (16%) of 50 and upstaging in 4 (8%) of 50 with gadolinium. Postneoadjuvant treatment, upstaging occurred in 1 (2%) of 50 from T2 to T3a. At baseline, mean distances from tumor to anorectal ring, anal verge, and mesorectal fascia were not statistically different with gadolinium. However, in 7 patients, differences could have resulted in treatment changes, accounted for by changes in relationships to anterior peritoneal reflection (n = 4), anorectal ring (n = 2), or anal verge (n = 1). Postneoadjuvant treatment, distances to anorectal ring and anal verge (in centimeters) were statistically smaller with gadolinium (p = 0.0017 and p = 0.0151) but could not have resulted in clinically significant treatment changes.

LIMITATIONS

This study was limited by its retrospective design.

CONCLUSIONS

The use of gadolinium at baseline MRI could have altered treatment in 24% of patients because of differences in tumor stage or position. Postneoadjuvant treatment, gadolinium resulted in statistically smaller distances to sphincters, which could influence surgical decision for sphincter-preserving rectal resection. See Video Abstract at http://links.lww.com/DCR/A444.

Clinical practice guidelines for the surgical treatment of rectal cancer: a consensus statement of the Hellenic Society of Medical Oncologists (HeSMO)

In rectal cancer management, accurate staging by magnetic resonance imaging, neo-adjuvant treatment with the use of radiotherapy, and total mesorectal excision have resulted in remarkable improvement in the oncological outcomes. However, there is substantial discrepancy in the therapeutic approach and failure to adhere to international guidelines among different Greek-Cypriot hospitals. The present guidelines aim to aid the multidisciplinary management of rectal cancer, considering both the local special characteristics of our healthcare system and the international relevant agreements (ESMO, EURECCA). Following background discussion and online communication sessions for feedback among the members of an executive team, a consensus rectal cancer management was obtained. Statements were subjected to the Delphi methodology voting system on two rounds to achieve further consensus by invited multidisciplinary international experts on colorectal cancer. Statements were considered of high, moderate or low consensus if they were voted by ≥80%, 60-80%, or <60%, respectively; those obtaining a low consensus level after both voting rounds were rejected. One hundred and two statements were developed and voted by 100 experts. The mean rate of abstention per statement was 12.5% (range: 2-45%). In the end of the process, all statements achieved a high consensus. Guidelines and algorithms of diagnosis and treatment were proposed. The importance of centralization, care by a multidisciplinary team, adherence to guidelines, and personalization is emphasized.

Does gadolinium-based contrast material improve diagnostic accuracy of local invasion in rectal cancer MRI? A multireader study

OBJECTIVE. The purpose of this study was to compare reader accuracy and agreement on rectal MRI with and without gadolinium administration in the detection of T4 rectal cancer. MATERIALS AND METHODS. In this study, two radiologists and one fellow independently interpreted all posttreatment MRI studies for patients with locally advanced or recurrent rectal cancer using unenhanced images alone or combined with contrast-enhanced images, with a minimum interval of 4 weeks. Readers evaluated involvement of surrounding structures on a 5-point scale and were blinded to pathology and disease stage. Sensitivity, specificity, negative predictive value, positive predictive value, and AUC were calculated and kappa statistics were used to describe interreader agreement. RESULTS. Seventy-two patients (38 men and 34 women) with a mean age of 61 years (range, 32-86 years) were evaluated. Fifteen patients had 32 organs invaded. Global AUCs without and with gadolinium administration were 0.79 and 0.77, 0.91 and 0.86, and 0.83 and 0.78 for readers 1, 2, and 3, respectively. AUCs before and after gadolinium administration were similar. Kappa values before and after gadolinium administration for pairs of readers ranged from 0.5 to 0.7. CONCLUSION. On the basis of pathology as a reference standard, the use of gadolinium during rectal MRI did not significantly improve radiologists' agreement or ability to detect T4 disease.

The impact of lymph node size to predict nodal metastasis in patients with rectal cancer after preoperative chemoradiotherapy

PURPOSE

During restaging after preoperative chemoradiotherapy (CRT), the assessment of lymph node (LN) metastasis is vital for selecting further treatment strategies. This study aimed to evaluate the impact of LN size to predict LN metastasis in rectal cancer patients after preoperative CRT.

METHODS

A total of 30 consecutive patients who underwent preoperative CRT followed by curative resection of primary rectal cancer were selected as a study group (CRT group). As a control group (non-CRT group), 30 patients who underwent primary tumor resection were selected using a 1:1 case-match design. Matching criteria were gender, age, and clinical T stage. The size of each LN was measured from the surgical specimen. To clarify optimal cutoff values for node size according to the risk of detecting metastasis, receiving-operator characteristic (ROC) curves were generated.

RESULTS

In the non-CRT group, 39/474 LNs were confirmed to have metastasis. In the CRT group, 29/422 LNs showed metastasis. The median size of metastatic LNs was 6.0 mm in CRT group, which was significantly larger than 4.0 mm in the non-CRT group (p = 0.006). The optimal cutoff value for determining metastasis in the CRT group was 4.5 mm, compared to 3.5 mm in the non-CRT group. The accuracy of the cutoff value was much higher in the CRT group (CRT vs. non-CRT, 77.9 vs. 59.9%).

CONCLUSIONS

LN size is a strong indicator for prediction of regional LN metastasis in rectal cancer patients after preoperative CRT, compared to those without CRT.

Computerized analysis of enhancement kinetics for preoperative lymph node staging in rectal cancer using dynamic contrast-enhanced magnetic resonance imaging

For this feasibility study, dynamic contrast-enhanced magnetic resonance imaging (dceMRI) was performed preoperatively in 9 patients with histologically proven rectal carcinoma. A total of 41 lymph nodes detected were matched to histopathology. Their contrast enhancement patterns were evaluated using computer-aided analysis and categorized in persistent, plateau, and washout curve type. Highest diagnostic accuracy for detecting malignancy was observed, when less than 31.8% of the voxels within a lymph node demonstrated a washout curve (sensitivity/specificity of 81.8%/89.7%; area under the curve, AUC=0.87). In comparison, conventional size measurements revealed lower AUC of 0.81 (sensitivity/specificity of 75%/72.4%). We conclude that dceMRI might be of diagnostic value for preoperative lymph node staging.

MR evaluation of rectal cancer: current concepts

Magnetic resonance imaging has become more frequently utilized for staging, preoperative planning, and post-neoadjuvant evaluation of rectal cancer. It offers detailed resolution of the layers of the rectal wall, visualization of the mesorectal fascia, and identification of locoregional nodal involvement. Many advances have been made since the original protocols and include the use of phased-array coils, orthogonally obtained images and 3-dimensional sequences, the use of diffusion-weighted and perfusion protocols to better evaluate the tumor before and after neoadjuvant therapy, and the development of techniques to better evaluate metastatic nodes. Magnetic resonance imaging shows similar accuracy to endorectal ultrasound when staging and offers a less invasive technique that is not limited by patient discomfort or decreased luminal size. This article is meant to provide an update on the recent advances in rectal cancer imaging while addressing the controversial issues that exist in staging, technique, and imaging protocol.

ACR Appropriateness Criteria pretreatment staging of colorectal cancer

Because virtually all patients with colonic cancer will undergo some form of surgical therapy, the role of preoperative imaging is directed at determining the presence or absence of synchronous carcinomas or adenomas and local or distant metastases. In contrast, preoperative staging for rectal carcinoma has significant therapeutic implications and will direct the use of radiation therapy, surgical excision, or chemotherapy. CT of the chest, abdomen, and pelvis is recommended for the initial evaluation for the preoperative assessment of patients with colorectal carcinoma. Although the overall accuracy of CT varies directly with the stage of colorectal carcinoma, CT can accurately assess the presence of metastatic disease. MRI using endorectal coils can accurately assess the depth of bowel wall penetration of rectal carcinomas. Phased-array coils provide additional information about lymph node involvement. Adding diffusion-weighted imaging to conventional MRI yields better diagnostic accuracy than conventional MRI alone. Transrectal ultrasound can distinguish layers within the rectal wall and provides accurate assessment of the depth of tumor penetration and perirectal spread, and PET and PET/CT have been shown to alter therapy in almost one-third of patients with advanced primary rectal cancer. The ACR Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed every 2 years by a multidisciplinary expert panel. The guideline development and review include an extensive analysis of current medical literature from peer-reviewed journals and the application of a well-established consensus methodology (modified Delphi) to rate the appropriateness of imaging and treatment procedures by the panel. In those instances in which evidence is lacking or not definitive, expert opinion may be used to recommend imaging or treatment.

A computer-aided algorithm to quantitatively predict lymph node status on MRI in rectal cancer

OBJECTIVE

The aim of this study was to demonstrate the principle of supporting radiologists by using a computer algorithm to quantitatively analyse MRI morphological features used by radiologists to predict the presence or absence of metastatic disease in local lymph nodes in rectal cancer.

METHODS

A computer algorithm was developed to extract and quantify the following morphological features from MR images: chemical shift artefact; relative mean signal intensity; signal heterogeneity; and nodal size (volume or maximum diameter). Computed predictions on nodal involvement were generated using quantified features in isolation or in combinations. Accuracies of the predictions were assessed against a set of 43 lymph nodes, determined by radiologists as benign (20 nodes) or malignant (23 nodes).

RESULTS

Predictions using combinations of quantified features were more accurate than predictions using individual features (0.67-0.86 vs 0.58-0.77, respectively). The algorithm was more accurate when three-dimensional images were used (0.58-0.86) than when only middle image slices (two-dimensional) were used (0.47-0.72). Maximum node diameter was more accurate than node volume in representing the nodal size feature; combinations including maximum node diameter gave accuracies up to 0.91.

CONCLUSION

We have developed a computer algorithm that can support radiologists by quantitatively analysing morphological features of lymph nodes on MRI in the context of rectal cancer nodal staging. We have shown that this algorithm can combine these quantitative indices to generate computed predictions of nodal status which closely match radiological assessment. This study provides support for the feasibility of computer-assisted reading in nodal staging, but requires further refinement and validation with larger data sets.

T-staging of rectal cancer: accuracy of 3.0 Tesla MRI compared with 1.5 Tesla

Objectives

Magnetic resonance imaging (MRI) is not accurate in discriminating T1-2 from borderline T3 rectal tumors. Higher resolution on 3 Tesla-(3T)-MRI could improve diagnostic performance for T-staging. The aim of this study was to determine whether 3T-MRI compared with 1.5 Tesla-(1.5T)-MRI improves the accuracy for the discrimination between T1-2 and borderline T3 rectal tumors and to evaluate reproducibility.

Methods

13 patients with non-locally advanced rectal cancer underwent imaging with both 1.5T and 3T-MRI. Three readers with different expertise evaluated the images and predicted T-stage with a confidence level score. Receiver operator characteristics curves with areas under the curve (AUC) and diagnostic parameters were calculated. Inter- and intra-observer agreements were calculated with quadratic kappa-weighting. Histology was the reference standard.

Results

Seven patients had pT1-2 tumors and six had pT3 tumors. AUCs ranged from 0.66 to 0.87 at 1.5T vs. 0.52–0.82 at 3T. Mean overstaging rate was 43% at 1.5T and 57% at 3T (P = 0.23). Inter-observer agreement was κ 0.50–0.71 at 1.5T vs. 0.15–0.68 at 3T. Intra-observer agreement was κ 0.71 at 1.5T and 0.76 at 3T.

Conclusions

This is the first study to compare 3T with 1.5T MRI for T-staging of rectal cancer within the same patients. Our results showed no difference between 3T and 1.5T-MRI for the distinction between T1-2 and borderline T3 tumors, regardless of expertise. The higher resolution at 3T-MRI did not aid in the distinction between desmoplasia in T1-2-tumors and tumor stranding in T3-tumors. Larger studies are needed to acknowledge these findings.

Local staging of rectal cancer: a review of imaging

During the past decades the management of patients with rectal cancer has substantially changed, with a significant reduction in local recurrence rates following the introduction of better imaging, better surgery, and more efficient neoadjuvant therapy. This review discusses the clinically relevant information radiologists should know on staging of rectal cancer patients. The crucial role of the radiologist in patient management is explained. Furthermore, the evidence for the use of magnetic resonance imaging (MRI) in staging and restaging of rectal cancer patients as well as the main features that need to be evaluated when interpreting rectal cancer MRI are given. New diagnostic challenges as a result of new treatment options are also discussed.

Evaluation of gadolinium-enhanced T1-weighted magnetic resonance imaging in the preoperative assessment of local staging in rectal cancer

AIM

The aim of this study was to determine whether gadolinium-enhanced T1-weighted magnetic resonance (MR) sequence is beneficial in the preoperative assessment of tumour and nodal staging in patients with primary rectal cancer.

METHOD

Eighty-eight patients with primary rectal cancer underwent preoperative MR imaging, followed by surgical resection. Two radiologists independently reviewed (i) T2-weighted MR images (T2WI); (ii) gadolinium-enhanced T1-weighted MR images (T1 + Gd); (iii) MR combined with T2WI and T1 + Gd for the prediction of tumour and nodal stage compared with histopathologic findings as the end point. Differences in the diagnostic performance of T2WI only, T1 + Gd image only and combined T2WI and T1 + Gd MR images were analyzed by comparing areas under receiver operating characteristic curves (Az) for each reader. Interobserver agreement was also calculated.

RESULTS

There was no significant difference in the Az values of T2WI only, T1 + Gd image only and combined T2WI and T1 + Gd images for the prediction of tumour staging (Az of T2WI, T1 + Gd and combined MR images for reader 1, 0.80, 0.76 and 0.85; reader 2, 0.83, 0.82 and 0.87) and nodal staging (Az for reader 1, 0.73, 0.73 and 0.81; reader 2, 0.79, 0.80 and 0.83). Interobserver agreement for the prediction of tumour staging was moderate to substantial, while only fair agreement was noted for the prediction of nodal staging.

CONCLUSION

Gadolinium-enhanced T1-weighted MRI did not increase the diagnostic yield for tumour and nodal staging, and may be omitted in the MR protocol for preoperative assessment of primary rectal cancer.

Preoperative staging of rectal cancer

Preoperative staging is now an essential factor in the multidisciplinary management of rectal cancer because tumor stage is the strongest predictive factor for recurrence. Preoperative staging of rectal cancer can be divided into either local or distant staging. Local staging incorporates the assessment of mural wall invasion, circumferential resection margin involvement, as well as the nodal status for metastasis. Distant staging assesses for evidence of metastatic disease. The aim of this review is to consider the indications and limitations of the current preoperative imaging modalities for rectal cancer staging including clinical examination, endorectal ultrasound, magnetic resonance imaging, computed tomography and positron emission tomography–computed tomography, with respect to local and distant disease.

A new rectal ultrasonographic method for the staging of rectal cancer

PURPOSE

Radial transrectal ultrasound is the most frequently used method for preoperative staging of rectal cancer. Accuracy rates of transrectal ultrasound have fallen significantly to 64% and 70% for tumor and node staging, respectively. The use of a frontal probe may overcome the drawbacks of radial transrectal ultrasound. This study was designed to compare the accuracy of frontal transrectal ultrasound performed with a frontal probe with the classic procedure, which uses a radial probe, in the preoperative T and N staging of rectal cancer.

METHODS

Seventy-four patients with rectal adenocarcinoma underwent both techniques. Thirty patients had a neoadjuvant treatment. The staging accuracy of both methods was determined by comparing the results of each with the findings of surgical histopathologic evaluation.

RESULTS

Forty-six men and 28 women were recruited. Frontal transrectal ultrasound was performed in all patients. Staging was amenable in only 58 patients with the radial transrectal ultrasound because the tumors were either stenotic or too proximal. Frontal transrectal ultrasound was accurate in the T staging of 89% of the tumors, whereas radial transrectal ultrasound was accurate in only 69% (P = 0.004). The difference was even more significant when we compared accuracy among the 58 patients in whom both examinations were completed (P = 0.002). Both methods had similar accuracy for lymph node staging. Neoadjuvant treatment had no influence on accuracy. No overstaging of the tumor occurred with the frontal transrectal ultrasound. Understaging was more frequently encountered with radial transrectal ultrasound than with frontal transrectal ultrasound (26% vs. 11%, respectively; P = 0.036).

CONCLUSION

Compared with radial transrectal ultrasound, frontal transrectal ultrasound has a better accuracy for T staging of rectal cancer. Its advantage in overcoming the drawbacks of radial transrectal ultrasound may make this procedure the method of choice for rectal cancer staging.

Lymph node size in rectal cancer following neoadjuvant chemoradiation--can we rely on radiologic nodal staging after chemoradiation?

OBJECTIVES

Local excision is currently being considered as an alternative strategy for ypT0-2 rectal cancer. However, patient selection is crucial to rule out nodal disease and is performed by radiologic studies that consider size as a surrogate marker for positive nodes. The purpose of this study was to determine the difference in size between metastatic and nonmetastatic nodes and the critical lymph node size after neoadjuvant chemoradiation therapy.

METHODS

The 201 lymph nodes available from 31 patients with ypT0-2 rectal cancer were reviewed and measured. Lymph nodes were compared according to the presence of metastases and size.

RESULTS

There was a mean of 6.5 lymph nodes per patient and 12 positive nodes of the 201 recovered (6%). Ninety-five percent of all lymph nodes were <5 mm, whereas 50% of positive lymph nodes were <3 mm. Metastatic lymph nodes were significantly greater in size (5.0 vs. 2.5mm; P = 0.02). Lymph nodes >4.5 mm had a greater risk of harboring metastases (P = 0.009).

CONCLUSIONS

Patients with ypT0-2 rectal cancer following neoadjuvant chemoradiation have very small perirectal nodes. Individual metastatic lymph nodes are significantly larger. However, a significant number of lymph nodes after neoadjuvant chemoradiation (negative and positive) are <3 mm. Individual lymph node size is not a good predictor of nodal metastases and may lead to inaccurate radiologic staging.

Magnetic resonance imaging of anorectal neoplasms

Among imaging techniques, magnetic resonance imaging (MRI) has evolved as the most robust technique for the detection, characterization, and staging of anorectal cancers. With its superior contrast resolution, multiplanar imaging capability, and nil radiation risk, it has become the standard preoperative imaging tool in rectal tumors. In this article we aim to outline the various types of anorectal cancers, highlight the complex anatomy of this region, and discuss the immensely useful role of MRI in the management of anorectal cancers. Existing limitations and future applications in this area will also be discussed. Because rectal adenocarcinomas constitute the majority of tumors in this region, we will be discussing the input of MRI in the management of this condition in greater detail. This will be followed by an overview of MRI in anal carcinoma and other less common anorectal neoplasms.

Rectal villous tumours: MR features and correlation with TRUS in the preoperative evaluation

AIM

The aim of this study was to assess the clinical relevance of MR and transrectal ultrasonography (TRUS) imaging of rectal villous tumours to elucidate the correlation between imaging results and specific histopathological tumour features, such as tumour size (T) and lymph node involvement (N), in order to establish the better technique for the pre-surgical patient evaluation.

PATIENTS AND METHODS

23 cases of villous tumours of the rectum were studied with phased-array MR and TRUS. All patients underwent either surgical or endoscopic treatment. Final diagnosis was based on histopathological results. In particular, the following features were characterized by the imaging techniques mentioned above: lesion site, distance between lesion and ano-rectal junction, size, morphology and contrast enhancement of lesions, fluid layer around the lesion, alterations of the deep layers of the rectal wall, sphincter infiltration, presence or absence of mesorectal, iliac and obturatory lymphnode involvement.

RESULTS

Histology established muscular involvement in 7 cases (T2), perirectal fat infiltration in 1 case (T3); in the remaining 15 cases, staging was Tis-T1. In 17/23 cases (73.9%) the lesions were correctly staged with both imaging techniques, whereas in 5/23 cases (21.7%) the lesions were overstaged. No cases were understaged. TRUS concorded with histological exams in 17/23 cases (73.9%). 5/23 cases (21.7%) were overstaged and 1/23 (4%) was understaged. MR and TRUS were in accordance in 20/23 cases (86.9%).

DISCUSSION

Considering the frequent degeneration of villous tumours, correct preoperative identification and precise evaluation of these lesions, such as the detection of rectal wall invasion, is essential in deciding optimal treatment strategy. MRI and TRUS allow the identification of specific features of villous tumours and of malignant degeneration, allowing for a correct local disease staging.

Local staging of rectal cancer using the black lumen magnetic resonance imaging technique

BACKGROUND AND AIMS

The treatment of rectal cancer is comprised of surgery and possible adjuvant therapy depending on the stage of the tumour. This prospective study evaluates the accuracy of magnetic resonance imaging (MRI) in the preoperative staging of rectal cancer using an endorectal and intravenous contrast.

MATERIALS AND METHODS

37 consecutive patients with rectal cancer were imaged using a mixture of ferumoxsil and methylcellulose endorectally, and a gadolinium contrast intravenously. 33 tumours were resected and 4 tumours were considered unresectable during operation. The images were reviewed for local staging of the tumours. A tumour confined to the rectal wall was classified as a negative finding and a tumour invading through muscularis propria as a positive finding. The results were correlated with the histopathologic t stage (n = 33), or the clinical status (n = 4).

RESULTS AND CONCLUSIONS

of 37 cases, 20 (51 %) were true positive, and 11 (28%) were true negative. There were 3 false negative and 3 false positive cases. The sensitivity was 87%, specificity 79%, and diagnostic accuracy 84%. for the non-contrast images the figures were 78%, 79% and 78%, respectively. We consider black lumen magnetic resonance imaging to be a useful method for preoperative local staging of rectal cancer.

Endorectal ultrasonography versus phased-array magnetic resonance imaging for preoperative staging of rectal cancer

AIM: To compare the diagnostic accuracy of pelvic phased-array magnetic resonance imaging (MRI) and endorectal ultrasonography (ERUS) in the preoperative staging of rectal carcinoma.

METHODS: Thirty-four patients (15 males, 19 females) with ages ranging between 29 and 75 who have biopsy proven rectal tumor underwent both MRI and ERUS examinations before surgery. All patients were evaluated to determine the diagnostic accuracy of depth of transmural tumor invasion and lymph node metastases. Imaging results were correlated with histopathological findings regarded as the gold standard and both modalities were compared in terms of predicting preoperative local staging of rectal carcinoma.

RESULTS: The pathological T stage of the tumors was: pT1 in 1 patient, pT2 in 9 patients, pT3 in 21 patients and pT4 in 3 patients. The pathological N stage of the tumors was: pN0 in 19 patients, pN1 in 9 patients and pN2 in 6 patients. The accuracy of T staging for MRI was 89.70% (27 out of 34). The sensitivity was 79.41% and the specificity was 93.14%. The accuracy of T staging for ERUS was 85.29% (24 out of 34). The sensitivity was 70.59% and the specificity was 90.20%. Detection of lymph node metastases using phased-array MRI gave an accuracy of 74.50% (21 out of 34). The sensitivity and specificity was found to be 61.76% and 80.88%, respectively. By using ERUS in the detection of lymph node metastases, an accuracy of 76.47% (18 out of 34) was obtained. The sensitivity and specificity were found to be 52.94% and 84.31%, respectively.

CONCLUSION: ERUS and phased-array MRI are complementary methods in the accurate preoperative staging of rectal cancer. In conclusion, we can state that phased-array MRI was observed to be slightly superior in determining the depth of transmural invasion (T stage) and has same value in detecting lymph node metastases (N stage) as compared to ERUS.

Comparison between 3-T magnetic resonance imaging and multi-detector row computed tomography for the preoperative evaluation of rectal cancer

OBJECTIVE

To compare prospectively between 3-T magnetic resonance imaging (MRI) and multidetector row computed tomography (MDCT) for the local staging of rectal cancer.

MATERIALS AND METHODS

During a recent 8-month period, both 3-T MRI with a phased array coil and MDCT scanner were used to preoperatively examine 31 consecutive patients. Preoperatively, the 3 experienced reviewers independently assessed the MRI and MDCT findings for the depth of tumor invasion into the rectal wall (T). Regional lymph node metastasis (N) was assessed by the 3 reviewers working in consensus. For T staging, we used a modified T staging (<or=T2, T3, and T4 staging). The results of the MRI and MDCT findings were compared based on the diagnosis of the resected specimens.

RESULTS

At histopathology, T1 was identified in 8 patients, T2 in 6, and T3 in 17 patients. The sensitivity, specificity, and accuracy for T2 staging or less between MRI and MDCT were 93% and 79%, 88% and 76%, and 91% and 77%, respectively. The sensitivity, specificity, and accuracy for T3 between MRI and MDCT were 92% and 73%, 93% and 83%, and 92% and 78%, respectively; there was a statistically significant difference for the T2 and T3 staging or less (P < 0.01). For N staging, MRI and CT can predict accurately in 88% and 77%, respectively (P > 0.05).

CONCLUSIONS

For local staging of rectal cancer, 3-T MRI is more accurate than MDCT for determining the depth of tumor invasion and the extent of lymph node metastasis.

Imaging and management of rectal cancer

Local staging and management of rectal cancer has evolved during the past decade. Imaging modalities used for staging rectal cancer include CT, endoscopic ultrasound, pelvic phased-array coil MRI, endorectal MRI, and PET. Each modality has its strengths and limitations. Evidence supports the use of both endoscopic ultrasound and CT in staging rectal cancer. MRI is the only reliable tool for determining the status of the circumferential resection margin, which is important for the assessment of the risk of local recurrence.

Prediction of lateral pelvic node involvement in low rectal cancer by conventional computed tomography

BACKGROUND

The clinical significance of lateral pelvic lymphatic spread in rectal cancer remains unknown. The present study aimed to assess the accuracy of preoperative computed tomography (CT) for prediction of lateral node involvement in patients with low rectal cancer and to determine the prognostic significance of extended lateral node dissection.

METHODS

A total of 109 patients with primary low rectal cancer were enrolled in this prospective cohort study. The preoperative CT findings were compared with the histopathological results and with follow-up data.

RESULTS

CT diagnosed lateral lymph node status with high accuracy (sensitivity 95 per cent, specificity 94 per cent), in marked contrast to mesorectal node status. Of 68 patients who had R0 resection without lateral node dissection, only two developed pelvic wall recurrence during median follow-up of 4.1 years. Metastatic nodes in the lateral pelvic region were significantly larger than those in the mesorectum (P < 0.001).

CONCLUSION

CT accurately predicted lateral lymph node status in low rectal cancer, allowing preoperative identification of patients who might benefit from extended lateral node dissection.

Effect of using endorectal coil in preoperative staging of rectal carcinomas by pelvic MR imaging

PURPOSE

To assess the accuracy of magnetic resonance imaging with pelvic phased-array and endorectal coils prospectively, and evaluate if endorectal coil provides any additional information to high resolution pelvic MR imaging in rectal carcinoma staging.

MATERIALS AND METHODS

Preoperative MRI of 25 patients with rectal carcinoma was performed with pelvic phased-array coil alone, and with both phased-array coil and endorectal coil placed. Staging was made by evaluating images obtained by using both coils prospectively, and correlated with histopathologic staging. The images were then assessed separately, and compared to each other retrospectively.

RESULTS

Two and 3 of the 5 histopathologically proved T1 tumors were staged correctly on MRI with pelvic phased-array coil alone and after the endorectal coil placement, respectively. Histopathologically identified five T2 tumors were staged correctly as T2 in 4 of the cases, 1 was understaged and 10 of 14 patients who had T3 tumor were staged as T3, 4 of them were understaged as T2 on both techniques. Specificity, sensitivity and accuracy rates for staging of T3 tumors were found as 71%, 100% and 84%, respectively, for each technique. Sensitivity and positive predictive value of N staging were both 88% on both techniques.

CONCLUSION

Pelvic MR imaging after the placement of endorectal coil in addition to the phase-array coil was not superior to the imaging with phased-array coil alone in T staging of rectal carcinomas and the latter achieved better visualization of the lymph nodes by means of larger field of view.

[Preoperative staging of rectal cancer]

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.

Preoperative Staging of Rectal Cancer: Comparison of 3-T High-Field MRI and Endorectal Sonography

OBJECTIVE

The aim of this study was to compare phased-array 3-T MRI and endorectal sonography in the preoperative staging of rectal cancer.

MATERIALS AND METHODS

During an 8-month period, 24 patients with rectal cancer underwent both 3-T MRI performed with phased-array coils and 7.5- to 10-MHz endorectal sonography in the 3 weeks before surgical resection. Three radiologists independently reviewed the MR and endorectal sonographic images. The histopathologic findings in resected specimens were used to evaluate the sensitivities and specificities of these techniques for invasion of the muscularis propria and perirectal tissue and for lymph node involvement. Receiver operating characteristic (ROC) analysis was used to compare the diagnostic accuracies of the techniques.

RESULTS

For muscularis propria invasion, the mean sensitivities of both MRI and endorectal sonography were 100%, and the mean specificities were 66.7% and 61.1%, respectively. The differences in the mean sensitivities and specificities were not statistically significant (p > 0.05 in each case). For perirectal tissue invasion, MRI and endorectal sonography had comparable sensitivities and specificities (91.1% vs 100%, 92.6% vs 81.5%; p > 0.05 in each case). They also had similar sensitivities and specificities for lymph node involvement (63.6% vs 57.6%, 92.3% vs 82.1%; p > 0.05 in each case). ROC curves for muscularis propria invasion and lymph node involvement showed no differences in diagnostic accuracy. The mean area under the ROC curve for endorectal sonography (A(Z) = 0.996) for perirectal tissue invasion, however, showed higher accuracy than that of MRI (A(Z) = 0.938, p = 0.028).

CONCLUSION

The sensitivity, specificity, and accuracy of 3-T MRI were similar to those of endorectal sonography for muscularis propria invasion and lymph node involvement, but for perirectal tissue invasion, 3-T MRI was less accurate than endorectal sonography.

Local staging of rectal cancer: the current role of MRI

With the advent of powerful gradient coil systems and high-resolution surface coils, magnetic resonance imaging (MRI) has recently extended its role in the staging of rectal cancer. MRI is superior to endorectal ultrasound, the most widely used staging modality in patients with rectal tumors, in that it visualizes not only the intestinal wall but also the surrounding pelvic anatomy. The crucial advantage of MRI is not that it enables exact T-staging but precise evaluation of the topographic relationship of a tumor to the mesorectal fascia. This fascia is the most important anatomic landmark for the feasibility of total mesorectal excision, which has evolved into the standard operative procedure for the resection of cancer located in the middle or lower third of the rectum. MRI is currently the only imaging modality that is highly accurate in predicting whether or not it is likely that a tumor-free margin can be achieved and thus provides important information for planning of an effective therapeutic strategy, especially in patients with advanced rectal cancer.

Preoperative staging of rectal cancer with MR Imaging: correlation with surgical and histopathologic findings

Rectal cancer is a common malignancy that continues to have a highly variable outcome, with local pelvic recurrence after surgical resection usually leading to incurable disease. The success of tumor excision depends largely upon accurate tumor staging and appropriate surgical technique, although the results of recent surgical trials indicate that evaluation of the involvement of the mesorectal fat and mesorectal fascia is even more important than T staging for treatment planning. Magnetic resonance (MR) imaging is increasingly being used to evaluate tumor resectability in patients with rectal cancer and to determine which patients can be treated with surgery alone and which will require radiation therapy to promote tumor regression. High-spatial-resolution MR imaging has proved useful in clarifying the relationship between a tumor and the mesorectal fascia, which represents the circumferential resection margin at total mesorectal excision. Phased-array surface coil MR imaging in particular plays a vital role in the therapeutic management of rectal cancer. At present, phased-array MR imaging best fulfills the clinical requirements for preoperative staging of rectal cancer. However, preoperative evaluation of the other prognostic factor, nodal status, is still problematic, and further studies will be needed to better define the role of MR imaging in this context.

Rectal carcinoma: high-spatial-resolution MR imaging and T2 quantification in rectal cancer specimens

PURPOSE

To prospectively compare high-spatial-resolution T1-weighted, T2-weighted, and intermediate-weighted spectral fat-saturated magnetic resonance (MR) imaging for the differentiation of tumor from fibrosis and for delineation of rectal wall layers in rectal cancer specimens.

MATERIALS AND METHODS

The local ethics committee approved the protocol, and written informed consent was obtained from each patient. Thin-section high-spatial-resolution MR imaging was performed in specimens obtained from 23 patients (16 men, seven women; median age, 64 years; age range, 39-84 years) immediately after resection. Seven patients underwent neoadjuvant treatment. T1-weighted spin-echo, T2-weighted fast spin-echo, and intermediate-weighted spectral fat-saturated MR images were obtained in the transverse plane. Differences in signal intensity between tumor and fibrosis and between tumor and rectal wall layers were evaluated by using visual scoring and measurements of T2 relaxation time. Statistical differences were evaluated by using the Wilcoxon signed rank test and a mixed-model regression analysis. All images were compared with whole-mount histopathologic slices (n = 86).

RESULTS

T2-weighted MR images provided the best differentiation between tumor and fibrosis (P < .001). Mean visual signal intensity scores were -1.8 for T2-weighted MR images, -1.4 for intermediate-weighted spectral fat-saturated MR images, and -0.2 for T1-weighted MR images. T2 relaxation times were 97 msec +/- 4.6 for tumor and 70 msec +/- 3.8 for fibrosis (P < .001). Substantial overlap was noted between the tumor and the circular layer of the muscularis propria (97 msec +/- 2.1), and less overlap was noted between the tumor and the longitudinal layer of the muscularis propria (88 msec +/- 1.6).

CONCLUSION

T2-weighted MR imaging provides superior delineation of rectal wall layers and better differentiation of tumor from fibrosis in rectal cancer specimens compared with T1-weighted MR imaging and intermediate-weighted spectral fat-saturated MR imaging by using thin-section high-spatial-resolution sequences.

Local staging of rectal cancer using combined pelvic phased-array and endorectal coil MRI

PURPOSE

To assess the accuracy of MRI, using a pelvic phased-array coil and an endorectal coil, for preoperative local staging of rectal cancer.

MATERIALS AND METHODS

Fifty-one patients (26 males and 25 females) with adenocarcinoma of the rectum underwent preoperative MRI and surgical resection of their tumors. Surgical pathology staging was compared to MRI staging (using the TNM classification) obtained both retrospectively by a reader blinded to surgical findings and prospectively (radiological reports). In addition, patients were stratified according to surgical treatment groups (stage I = T1-2/N0, stage II = T3/N0, stage III = Tx/N1-2).

RESULTS

At pathology, 36 of 51 (68%) tumors were classified as T0-T2, and 15 (32%) were classified as T3. Overall, the sensitivity and specificity of MRI readings for T3 staging were 93% and 86%, respectively (positive predictive value (PPV) = 74%, negative predictive value (NPV) = 97%, accuracy = 88%). MRI correctly predicted lymph node metastases in 11 of 13 patients with a sensitivity of 85% and specificity of 69% (PPV = 58%, NPV = 90%, accuracy = 74%). MRI correctly predicted surgical treatment groups in 33 of 39 (85%) patients. Interobserver agreement between the retrospective and prospective readings was excellent (kappa = 0.85) for prediction of T3 tumor and good (kappa = 0.80) for prediction of nodal involvement.

CONCLUSION

Combined endorectal and pelvic phased-array coil MRI can be used reliably to select which patients should receive preoperative chemoradiotherapy. It is highly predictive in terms of excluding T3 tumors, but still has limitations in predicting lymph node metastasis.