Thin-Section MRI with a Phased-Array Coil for Preoperative Evaluation of Pelvic Anatomy and Tumor Extent in Patients with Rectal Cancer

Primary staging of rectal cancer on MRI: an updated pictorial review with focus on common pitfalls and current controversies

Magnetic resonance imaging (MRI) plays a pivotal role in primary staging of rectal cancer, enabling the determination of appropriate management strategies and prediction of patient outcomes. However, inconsistencies and pitfalls exist in various aspects, including rectal anatomy, MRI protocols and strategies for artifact resolution, as well as in T- and N-staging, all of which limit the diagnostic value of MRI. This narrative and pictorial review offers a comprehensive overview of factors influencing primary staging of rectal cancer and the role of MRI in assessing them. It highlights the significance of the circumferential resection margin and its relationship with the mesorectal fascia, as well as the prognostic role of extramural venous invasion and tumor deposits. Special attention is given to tumors of the lower rectum due to their complex anatomy and the challenges they pose in MRI staging. The review also addresses current controversies in rectal cancer staging and the need for personalized risk stratification. In summary, this review provides valuable insights into the role of MRI in the primary staging of rectal cancer, emphasizing key aspects for accurate assessment to enhance patient outcomes.

Biparametric magnetic resonance imaging-based radiomics features for prediction of lymphovascular invasion in rectal cancer

BACKGROUND

Preoperative assessment of lymphovascular invasion(LVI) of rectal cancer has very important clinical significance. However, accurate preoperative imaging evaluation of LVI is highly challenging because the resolution of MRI is still limited. Relatively few studies have focused on prediction of LVI of rectal cancer with the tool of radiomics, especially in patients with negative statue of MRI-based extramural vascular invasion (mrEMVI).The purpose of this study was to explore the preoperative predictive value of biparametric MRI-based radiomics features for LVI of rectal cancer in patients with the negative statue of mrEMVI.

METHODS

The data of 146 cases of rectal adenocarcinoma confirmed by postoperative pathology were retrospectively collected. In the cases, 38 had positive status of LVI. All patients were examined by MRI before the operation. The biparametric MRI protocols included T2-weighted imaging (T2WI) and diffusion-weighted imaging (DWI). We used whole-volume three-dimensional method and two feature selection methods, minimum redundancy maximum relevance (mRMR) and least absolute shrinkage and selection operator (LASSO), to extract and select the features. Logistics regression was used to construct models. The area under the receiver operating characteristic curve (AUC) and DeLong's test were used to evaluate the diagnostic performance of the radiomics based on T2WI and DWI and the combined models.

RESULTS

Radiomics models based on T2WI and DWI had good predictive performance for LVI of rectal cancer in both the training cohort and the validation cohort. The AUCs of the T2WI model were 0.87 and 0.87, and the AUCs of the DWI model were 0.94 and 0.92. The combined model was better than the T2WI model, with AUCs of 0.97 and 0.95. The predictive performance of the DWI model was comparable to that of the combined model.

CONCLUSIONS

The radiomics model based on biparametric MRI, especially DWI, had good predictive value for LVI of rectal cancer. This model has the potential to facilitate the clinical recognition of LVI in rectal cancer preoperatively.

Accuracy of MRI in early rectal cancer: national cohort study

MRI plays a pivotal role in the staging of early rectal cancer, resulting in allocation of patients to surgery or organ-sparing treatment. In this large population-based retrospective cohort study, MRI substantially understaged pT3 and overstaged pT1 rectal cancer, in addition to unreliable nodal staging. Based on these findings, MRI is not adequate in allocating patients with rectal cancer to organ-sparing treatment.

MRI Staging in an Evolving Management Paradigm for Rectal Cancer, From the AJR Special Series on Cancer Staging

The treatment of rectal cancer centers around the distinct but related goals of management of distant metastases and management of local disease. Optimal local management requires attention to the primary tumor and its anatomic relationship to surrounding pelvic structures, with the goal of minimizing local recurrence (LR). High-resolution MRI is ideally suited for this purpose; application of MRI-based criteria in conjunction with optimized surgical and pathologic techniques have successfully reduced LR rates. This success has led to a shift away from using the TNM-based National Comprehensive Cancer Network (NCCN) guidelines as the sole determinant of whether a patient receives neoadjuvant chemoradiation. The new model uses a hybrid approach for assigning risk categories that combines elements of the TNM staging system with MRI-based anatomic features. These risk categories incorporate tumor proximity to the circumferential resection margin, T category, distance to the anal verge and presence of extramural venous invasion, to classify rectal tumors as low, intermediate, or high-risk. This approach has been validated by accumulated data from numerous multi-institutional studies. This review illustrates key anatomic concepts, depicts common interpretive errors and pitfalls, and discusses ongoing limitations; these insights should guide radiologists in optimal rectal MRI interpretation.

Improving staging of rectal cancer in the pelvis: the role of PET/MRI

PURPOSE

The role of positron emission tomography/magnetic resonance (PET/MR) in evaluating the local extent of rectal cancer remains uncertain. This study aimed to investigate the possible role of PET/MR versus magnetic resonance (MR) in clinically staging rectal cancer.

METHODS

This retrospective two-center cohort study of 62 patients with untreated rectal cancer investigated the possible role of baseline staging PET/MR versus stand-alone MR in determination of clinical stage. Two readers reviewed T and N stage, mesorectal fascia involvement, tumor length, distance from the anal verge, sphincter involvement, and extramural vascular invasion (EMVI). Sigmoidoscopy, digital rectal examination, and follow-up imaging, along with surgery when available, served as the reference standard.

RESULTS

PET/MR outperformed MR in evaluating tumor size (42.5 ± 21.03 mm per the reference standard, 54 ± 20.45 mm by stand-alone MR, and 44 ± 20 mm by PET/MR, P = 0.004), and in identifying N status (correct by MR in 36/62 patients [58%] and by PET/MR in 49/62 cases [79%]; P = 0.02) and external sphincter infiltration (correct by MR in 6/10 and by PET/MR in 9/10; P = 0.003). No statistically significant differences were observed in relation to any other features.

CONCLUSION

PET/MR provides a more precise assessment of the local extent of rectal cancers in evaluating cancer length, N status, and external sphincter involvement. PET/MR offers the opportunity to improve clinical decision-making, especially when evaluating low rectal tumors with possible external sphincter involvement.

Rectal cancer MR staging: pearls and pitfalls at baseline examination

In recent years, rectal MRI has become a central diagnostic tool in rectal cancer staging. Indeed, rectal MR has the ability to accurately evaluate a number of important findings that may impact patient management, including distance of the tumor to the mesorectal fascia, presence of extramural vascular invasion (EMVI), presence of lymph nodes, and involvement of the peritoneum/anterior peritoneal reflection. Many of these findings are difficult to assess in nonexpert hands. In this review, we present a practical approach for radiologists to provide high-quality interpretations at initial baseline exams, based on recent guidelines from the Society of Abdominal Radiology, Rectal and Anal Cancer Disease Focused Panel. Practical pearls and pitfalls are discussed, focusing on optimization of technique including, patient preparation and protocol recommendations, interpretation, and essentials of reporting.

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.

Net survival of patients with colorectal cancer: a comparison of two periods

BACKGROUND

The purpose of our analysis was to compare the results of treatment in patients who underwent resection for colorectal carcinoma.

METHODS

In the period from 1/1/1991 to 31/12/2000 1478 patients with colorectal carcinoma underwent potentially curative resection. We divided them into two 5-year period groups according to different treatment regimes. The 5-year net survival rate was estimated, where the net survival is the probability of survival derived solely from the cancer-specific hazard.

RESULTS

In a 10-year period, we resected 1478 patients. The 5-year net survival rate for R0-resected patients with colon cancer increased from 76.3 to 85.2% between the periods 1991-1995 and 1995-2000. The 5-year net survival rate for R0-resected patients with rectal cancer also increased from 67.5 to 73% in the same period.

CONCLUSION

A comparison of the 5-year net survival rate for R0-resected patients with colorectal cancer increased in the last period from 1995 to 2000 compared with the period from 1991 to 1995. In multivariate analysis, early stage at diagnosis and adjuvant chemotherapy was both associated with better net survival after surgery with curative intent. The improvement of net survival is potentially the result of combination of better surgical and adjuvant therapy.

Assessing surgical difficulty in locally advanced mid-low rectal cancer: the accuracy of two MRI-based predictive scores

AIM

Predicting surgical difficulty is a critical factor in the management of locally advanced rectal cancer (LARC). This study evaluates the accuracy and external validity of a recently published morphometric score to predict surgical difficulty and additionally proposes a new score to identify preoperatively LARC patients with a high risk of having a difficult surgery.

METHODS

This is a retrospective study based on the European MRI and Rectal Cancer Surgery (EuMaRCS) database, including patients with mid/low LARC who were treated with neoadjuvant chemoradiation therapy and laparoscopic total mesorectal excision (L-TME) with primary anastomosis. For all patients, pretreatment and restaging MRI were available. Surgical difficulty was graded as high and low based upon a composite outcome, including operative (e.g. duration of surgery) and postoperative variables (e.g. hospital stay). Score accuracy was assessed by estimating sensitivity, specificity and area under the receiver operating characteristic curve (AROC).

RESULTS

In a total of 136 LARC patients, 17 (12.5%) were graded as high surgical difficulty. The previously published score (calculated on body mass index, intertuberous distance, mesorectal fat area, type of anastomosis) showed low predictive value (sensitivity 11.8%; specificity 92.4%; AROC 0.612). The new EuMaRCS score was developed using the following significant predictors of surgical difficulty: body mass index > 30, interspinous distance < 96.4 mm, ymrT stage ≥ T3b and male sex. It demonstrated high accuracy (AROC 0.802).

CONCLUSION

The EuMaRCS score was found to be more sensitive and specific than the previous score in predicting surgical difficulty in LARC patients who are candidates for L-TME. However, this score has yet to be externally validated.

Preoperative T staging using CT colonography with multiplanar reconstruction for very low rectal cancer

Background

Preoperative T staging of lower rectal cancer is an important criterion for selecting intersphincteric resection (ISR) or abdominoperineal resection (APR) as well as selecting neoadjuvant therapy. The aim of this study was to evaluate the accuracy of preoperative T staging using CT colonography (CTC) with multiplanar reconstruction (MPR), in which with the newest workstation the images can be analyzed with a slice thickness of 0.5 mm.

Methods

Between 2011 and 2013, 45 consecutive patients with very low rectal adenocarcinoma underwent CTC with MPR. The accuracy of preoperative T staging using CTC with MPR was evaluated. The accuracy of preoperative T staging using MRI in the same patient population (34 of 45 patients) was also examined.

Results

Overall accuracy of T staging was 89% (41/45) for CTC with MPR and 71% (24/34) for MRI. CTC with MPR was particularly sensitive for pT2 tumors (82%; 14/17), whereas MRI tended to overstage pT2 tumors and its sensitivity for pT2 was 53% (8/15).

Conclusions

CTC with MPR, with an arbitrary selection, could be aligned to the tumor axis and better demonstrated tumor margins consecutively including the deepest section of the tumor. The accuracy of T2 and T3 staging using CTC with MPR seemed to surpass that of MRI, suggesting a potential role of CTC with MPR in preoperative T staging for very low rectal cancer.

Comparison of the pathological response of the mesorectal positive nodes between short-course chemoradiotherapy with delayed surgery and long-course chemoradiotherapy in patients with rectal cancer

BACKGROUND

The aim of this study was to compare the pathological response of mesorectal positive nodes between short-course chemoradiotherapy with delayed surgery (SCRT-delay) and long-course chemoradiotherapy (LC-CRT) in patients with rectal cancer.

METHOD

The resected primary tumor specimens following the two different approaches were assessed utilizing the tumor regression grade (TRG 0-4), and each positive lymph node was assessed according to the lymph node regression grade (LRG 1-3), with TRG 4 and LRG 3 indicating total regression. The lymph node sizes were measured to elucidate any correlation with LRG scores.

RESULTS

Seventy-four patients with ypN-positive rectal cancer had 220 positive lymph nodes following the SCRT-delay, and 48 patients had 141 positive lymph nodes following the LC-CRT. The distribution of LRG 1/2/3 in the two groups was 123/72/25 and 60/31/50 (p < 0.001), respectively, and the distribution of TRG 0/1/2/3/4 in the two groups was 36/19/19/0 and 12/15/20/1 (p = 0.005), respectively. The requirements of total regression of positive lymph nodes were a primary tumor degenerated to TRG 3 with a size less than 6 mm in SCRT-delay (sensitivity, 60.9 %) or a primary tumor degenerated to TRG 2-4 with a size less than 5 mm at TRG 2 (sensitivity, 57.6 %) or 6 mm at TRG 3 and 4 (sensitivity, 84.2 %) in LC-CRT as indicated by the receiver operating characteristic curve analysis.

CONCLUSION

The tumor regression effect of LC-CRT on the primary tumor and positive nodes was more favorable than SCRT-delay, and LC-CRT is able to predict the LRG 3 response with a high sensitivity.

Preoperative evaluation of lymphovascular invasion using high-resolution pelvic magnetic resonance in patients with rectal cancer: a 2-year follow-up study

OBJECTIVES

The objectives of this study were to preoperatively evaluate lymphovascular invasion (LVI) using pelvic magnetic resonance (MR) in patients with rectal cancer and to determine the correlation with distant metastasis rate.

METHODS

If the mesorectal perivascular infiltrative signal was visible on pelvic MR imaging, the possibility of LVI was recorded. Distant metastatic lesions were also recorded at the time of the initial diagnostic workup and over a 2-year follow-up period.

RESULTS

Fifteen (68.2%) of the 22 LVI patients showed mesorectal perivascular infiltrative signals on pelvic MRI. For the prediction of LVI in rectal cancer, MR had a sensitivity of 68.2% and a specificity of 93.2. The initial distant metastasis rate was significantly higher in patients with MR LVI (52%) than in patients without MR LVI (5.7%) (P < 0.0001).

CONCLUSIONS

On pelvic MR, the presence of mesorectal perivascular infiltration by nodes is a specific sign of LVI in rectal cancer, and the presence of LVI is a predictor of distant metastasis.

[Importance of whole body MRI for staging of colorectal cancer]

CLINICAL/METHODICAL ISSUE

Staging and follow-up of colorectal cancer are usually performed with multimodal imaging strategies. These can be time-intensive and potentially lead to examiner-dependent bias. Alternatively, whole body magnetic resonance imaging (WB-MRI) provides oncologic imaging with a systemic approach.

STANDARD RADIOLOGICAL METHODS

Ultrasound, multislice computed tomography (MSCT), dedicated MRI and positron emission tomography/CT (PET/CT).

METHODICAL INNOVATIONS

High-resolution WB-MRI with focused examination of various organs, such as the pelvis and abdomen, lungs, brain and skeletal system, using different sequence and contrast techniques.

PERFORMANCE

Detection of colorectal tumor recurrence with WB-MRI provides 83% accuracy (lymph node metastases 80%, organ metastases 86%).

ACHIEVEMENTS

Potential cost reduction through decreased examination time and personnel costs.

PRACTICAL RECOMMENDATIONS

Whole body MRI is a radiation-free alternative to standard sequential algorithms of staging and follow-up of colorectal cancer.

Rectal Cancer: MR imaging of the mesorectal fascia and effect of chemoradiation on assessment of tumor involvement

PURPOSE

To evaluate the impact of chemoradiation on the reliability of MRI in assessing tumor involvement of the mesorectal fascia in patients with rectal cancer.

MATERIALS AND METHODS

Presurgical MRI was performed in 150 patients; among them 85 had received neoadjuvant long-course chemoradiation. A standardized imaging protocol (1.5 Tesla [T] system, image voxel size 0.6 × 0.4 × 3 mm(3) ), standardized surgery, and histopathological examination were applied for the entire patient population. Images were analyzed to identify potential tumor involvement of the mesorectal fascia (minimum tumor distance to fascia ≤1 mm) and compared with histopathology as the reference standard. Results of nonirradiated and irradiated patients were compared to define the impact of chemoradiation on imaging reliability.

RESULTS

In nonirradiated patients, MRI was reliable in predicting or excluding tumor involvement of the mesorectal fascia, positive predictive value 80%, negative predictive value 89%. The frequency of overestimating tumor involvement was significantly higher in irradiated patients (P = 0.005, positive predictive value 42%).

CONCLUSION

Discussions about MRI assessment of tumor involvement of the mesorectal fascia as a basis for recommending neoadjuvant chemoradiation should focus on investigations that excluded irradiated patients, because MRI is less reliable after chemoradiation and tends to overestimate mesorectal tumor involvement.

Rectal cancer: comparison of accuracy of local-regional staging with two- and three-dimensional preoperative 3-T MR imaging

PURPOSE

To compare the local-regional staging accuracy of the conventional two-dimensional (2D) T2-weighted imaging protocol and of the three-dimensional (3D) T2-weighted imaging protocol for preoperative magnetic resonance (MR) imaging in rectal cancer patients.

MATERIALS AND METHODS

This retrospective study was approved by the institutional review board, and a waiver of informed consent was obtained. A review was conducted of 109 preoperative 3-T MR images obtained with 2D and 3D T2-weighted imaging protocols in rectal cancer patients. Two radiologists independently assessed the radiologic findings for T and N category lesions, conspicuity of tumor margin, and image quality of 2D and 3D data. Interactive multiplanar reconstruction was performed for 3D data analysis. The linear weighted kappa values for T2-weighted imaging staging results (2D and 3D data) and histopathologic staging results were calculated and compared. Wilcoxon signed rank test was performed to compare tumoral conspicuity and overall image quality.

RESULTS

T category lesion staging accuracy values for 2D and 3D data, respectively, were 66.0% and 67.0% for reviewer 1 (P = .465) and 63.3% and 56.9% for reviewer 2 (P = .402). N category lesion staging accuracy values for 2D and 3D T2-weighted images, respectively, were 64.2% and 57.8% for reviewer 1 (P = .427) and 47.7% and 62.4% for reviewer 2 (P = .666). Tumor conspicuity was better for 2D T2-weighted imaging, but no significant difference in image quality was observed.

CONCLUSION

Preoperative MR imaging in rectal cancer patients for staging with conventional 2D and multiplanar reconstruction 3D T2-weighted imaging protocols showed no significant differences in accuracy of T and N category staging and overall image quality, as determined by degree of artifact. However, the 3D T2-weighted imaging protocol had limitations in regard to lesion conspicuity.

Male urinary and sexual functions after mesorectal excision alone or in combination with extended lateral pelvic lymph node dissection for rectal cancer

BACKGROUND

Mesorectal excision reduced the incidence of genitourinary dysfunction compared with conventional surgery. In Japan, extended lateral pelvic lymph node dissection (ELD) is added to mesorectal excision when lateral pelvic node metastasis is suspected. The aim of this study was to evaluate male genitourinary function after mesorectal excision or mesorectal excision plus ELD for rectal cancer.

METHODS

According to the degree of pelvic-plexus preservation (PPP) and ELD, patients were grouped into PG1, mesorectal excision alone (bilateral PPP without ELD) (n = 27); PG2, bilateral PPP with ELD (n = 12); PG3, unilateral PPP with ELD (n = 26); and PG4, no PPP with ELD (n = 4). The assessment included measurements of the time interval to residual urine becoming <50 mL, interviews assessing sexual function, and nocturnal penile tumescence measurements.

RESULTS

Proportions of patients with residual urine becoming <50 mL within 14 days after surgery were 96% in PG1, 73% in PG2, 23% in PG3, and 0% in PG4 (P < .001). Proportions of patients answering the ability to maintain sexual intercourse at 1 year were 95% in PG1, 56% in PG2, 45% in PG3, and 0% in PG4 (P < .001). Proportions of patients having nocturnal penile rigidity of >65% at 1 year were 95% in PG1, 33% in PG2, 50% in PG3, and 0% in PG4 (P < .001).

CONCLUSIONS

Patients undergoing mesorectal excision alone can expect excellent genitourinary function, but functional results after mesorectal excision plus ELD are far worse. Degrees of dysfunction depend on the extents of both autonomic nerve resection and ELD.

Accuracy of high-resolution magnetic resonance imaging in preoperative staging of rectal cancer

BACKGROUND

To achieve better prognosis and quality of life for patients with rectal cancer, extent of surgery and neoadjuvant chemoradiotherapy should accurately reflect disease extent. The aim of this study was to evaluate accuracy of high-resolution magnetic resonance imaging (HRMRI) for preoperative staging of rectal cancer.

METHODS

Between 2001 and 2003, 104 patients with primary rectal cancer were examined with HRMRI and underwent radical surgery. Transmural invasion depth and lymph node metastasis were assessed prospectively and classified according to the American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) system by both HRMRI and histopathology, and results were compared. Criteria for mesorectal and lateral pelvic lymph node involvement were short-axis diameters of > or =5 mm and > or =4 mm, respectively.

RESULTS

There were 15 pT1, 25 pT2, 50 pT3, and 14 pT4 tumors. Overall accuracy rate for transmural invasion depth was 84%. The mesorectal fascia could be visualized in 98% of patients. Twenty-three patients had mesorectal fascia involvement and the overall accuracy rate was 96% (sensitivity, 96%; specificity, 96%). Fifty-three patients had mesorectal lymph node metastasis and the overall accuracy rate was 74% (sensitivity, 83%; specificity, 64%). Lateral pelvic lymph node metastasis was observed in 15 patients and the overall accuracy rate was 87% (sensitivity, 87%; specificity, 87%).

CONCLUSIONS

HRMRI was moderately accurate for prediction of mesorectal lymph node metastasis and highly accurate regarding transmural invasion depth, and mesorectal fascia and lateral pelvic node involvement. Therefore, HRMRI appears useful for preoperative decision-making in rectal cancer treatment.

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.

Preoperative staging of rectal cancer

Detailed preoperative staging using high resolution magnetic resonance imaging (MRI) enables the selection of patients that require preoperative therapy for tumour regression. This information can be used to instigate neoadjuvant therapy in those patients with poor prognostic features prior to disturbing the tumour bed and potentially disseminating disease. The design of trials incorporating MR assessment of prognostic factors prior to therapy has been found to be of value in assessing treatment modalities and outcomes that are targeted to these preoperative prognostic subgroups and in providing a quantifiable assessment of the efficacy of particular chemoradiation treatment protocols by comparing pre-treatment MR staging with post therapy histology assessment. At present, we are focused on achieving clear surgical margins of excision (CRM) to avoid local recurrence. We recommend that all patients with rectal cancer should undergo pre-operative MRI staging. Of these, about half will have good prognosis features (T1-T3b, N0, EMVI negative, CRM clear) and may safely undergo primary total mesorectal excision. Of the remainder, those with threatened or involved margins will certainly benefit from pre-operative chemoradiotherapy with the aim of downstaging to permit safe surgical excision. In the future, our ability to recognise features predicting distant failure, such as extramural vascular invasion (EMVI) may be used to stratify patients for neo-adjuvant systemic chemotherapy in an effort to prevent distant relapse. The optimal pre-operative treatment regimes for these patients (radiotherapy alone, systemic chemotherapy alone or combination chemo-radiotherapy) is the subject of current and future trials.

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.

Preoperative 3T MR imaging of rectal cancer: local staging accuracy using a two-dimensional and three-dimensional T2-weighted turbo spin echo sequence

PURPOSE

The purpose of our study was to evaluate the image quality and diagnostic performance of two-dimensional (D) turbo spin echo (TSE) and 3D T2-weighted TSE MR imaging in local staging of rectal cancer at 3T.

MATERIALS AND METHODS

3T phased-array MR imaging was performed in 36 consecutive patients with biopsy-proven rectal cancer. High-resolution 2D TSE images in three planes and 3D TSE images of the rectum were obtained. Two independent observers performed an image quality assessment using eight image quality characteristics. All 2D and 3D datasets were evaluated separately. MR images were prospectively evaluated by two experienced radiologists in consensus with regard to local disease. Total mesorectal excision was used as the standard of reference. The sensitivity, specificity, positive and negative predictive value, and overall accuracy were calculated. Areas under the receiver operating characteristic (ROC) curve (AUC) were determined.

RESULTS

Twenty-two patients who underwent a total mesorectal excision were enrolled in this study. Significantly more motion artifacts were present with 3D TSE imaging (P=0.04). The overall sensitivity, specificity, and accuracy of muscularis propria invasion in rectal cancer using 2D T2-weighted images were 100%, 66%, and 95%, respectively. There was a statistical significant greater AUC using 2D T2-weighted images compared to 3D T2-weighted MR images (P=0.04). The ROC curves describing the results of the interpretation of 2D and 3D T2-weighted datasets regarding perirectal tissue invasion showed no statistical significant difference (P=0.41).

CONCLUSIONS

In this study, high local staging accuracies with 3T 2D T2-weighted MR imaging were demonstrated. 3D T2-weighted MR imaging cannot replace 2D MR imaging for local staging of rectal cancer. However, 3D MR imaging can be used for visualization of the complex pelvic anatomy for treatment planning purposes.

Post-treatment fistulas in patients with rectal cancer: MRI with rectal superparamagnetic contrast agent

MRI is the standard modality in the pre- and post-treatment evaluation of patients with rectal cancer, particularly in those cases with locally advanced disease. We routinely employ a superparamagnetic iron oxide (SPIO) contrast enema to distend the rectal lumen and achieve maximal tumor-to-lumen contrast gradient. This practice also allowed the identification of a fistula in 24% of patients treated for rectal cancer. Contrast agent-related low intensity signal could be seen filling the tract and eventually opacifying surrounding organs (i.e., vagina) or collections (i.e., presacral abscess). Fistula formation after radiochemotherapy and surgery for rectal cancer is not uncommon. MRI with dark lumen contrast enema allows an effective demonstration of this complication in a high number of patients.

Limitations of early rectal cancer nodal staging may explain failure after local excision

Successful selection of patients with rectal cancer for local excision requires accurate preoperative lymph node staging. Although endorectal ultrasound is capable of detecting locally advanced disease, its ability to correctly identify nodal metastases in early rectal lesions is less well described. This study examines the accuracy of endorectal ultrasound in determining nodal stage based on depth of penetration of the primary lesion (T stage). Between 1998 and 2003, endorectal ultrasound was performed on 938 consecutive patients; 134 had biopsy-proven rectal cancers and were treated with radical resection, without neoadjuvant therapy. Lymph node metastases were measured pathologically and correlated with endorectal ultrasound and clinicopathologic features. Accuracy and specificity of endorectal ultrasound nodal staging was determined. The overall accuracy of endorectal ultrasound nodal staging for the study cohort was 70 percent, with a 16 percent false-positive rate and 14 percent false-negative rate. Endorectal ultrasound was more likely to overlook small metastatic lymph node deposits. The size of lymph node metastasis and accuracy of endorectal ultrasound nodal staging was related to T stage. The specificity of endorectal ultrasound nodal staging, or the ability to identify patients who were node-negative, was dependent on T stage. Early rectal lesions are more likely to have lymph node micrometastases not detected by endorectal ultrasound. The ability of endorectal ultrasound to correctly identify patients without lymph node metastasis is dependent on the T stage of the primary lesion. The limitations of endorectal ultrasound in accurately staging nodal disease in early rectal lesions may, in part, explain the relatively high recurrence rates seen after local excision.

[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.

[External phased-array MR imaging preoperative assessment of rectal cancer]

The main problem associated with rectal cancer treatment is tumor recurrence. Randomized controlled studies have shown that adjuvant preoperative radiation therapy is effective for reducing local recurrence. These studies have also demonstrated that there are groups of rectal cancer patients with differing degrees of risk for local recurrence. At one end of the spectrum is the low-risk group: patients with superficial rectal cancer, who can be treated with surgery alone. At the other end is the high-risk group: patients with a close or involved resection margin at total mesorectal excision, the very advanced tumors that require a longer course of chemotherapy and radiation therapy, and extensive surgery. Paramount for this selection and differentiated treatment is a reliable preoperative test that can be used to distinguish these groups of patients. In this review article, we will discuss the role of high-resolution phased array MRI among the other imaging modalities such as endorectal MRI, endorectal US, and CT. We will also discuss and illustrate MR imaging results in terms of T stage, circumferential resection margin, locally advanced rectal cancer, and N stage.

Clinicopathological significance of microscopic abscess formation at the invasive margin of advanced low rectal cancer

BACKGROUND

The aim of this study was to evaluate the clinicopathological significance of microscopic abscess formation (MAF) at the invasive front of advanced low rectal cancer.

METHODS

The clinicopathological features of 226 consecutive patients with low rectal cancer, who underwent curative resection between May 1997 and December 2002, were analysed.

RESULTS

Fifty-seven (25.2 per cent) of the 226 tumours had MAF and 169 (74.8 per cent) did not. Patients with tumours showing MAF were more likely to have extended surgery than those without MAF: 47 versus 31.4 per cent respectively underwent non-sphincter-preserving surgery (P=0.029) and 82 versus 60.9 per cent underwent lateral lymph node dissection (P=0.003). The incidence of lymph node metastases was lower in patients with MAF (30 versus 53.3 per cent; P=0.002). Univariable analysis of disease-free survival revealed that depth of invasion (P<0.001), lymph node status (P<0.001), histological type (P=0.035), lymphatic invasion (P<0.001), venous invasion (P<0.001), perineural invasion (P<0.001), focal dedifferentiation (P<0.001) and MAF (P<0.001) were significant prognostic factors. Multivariable analysis showed that lymph node status (P<0.001), perineural invasion (P=0.002), venous invasion (P=0.033) and MAF (P=0.012) remained independent prognostic factors.

CONCLUSION

MAF may reflect indolent tumour behaviour and a more favourable outcome in patients with advanced low rectal cancer.

Magnetic Resonance Imaging of the Body Trunk Using a Single-Slab, 3-Dimensional, T2-weighted Turbo-Spin-Echo Sequence With High Sampling Efficiency (SPACE) for High Spatial Resolution Imaging

PURPOSE

The authors conducted a clinical evaluation of single-slab, 3-dimensional, T2-weighted turbo-spin-echo (TSE) with high sampling efficiency (SPACE) for high isotropic body imaging with large field-of-view (FoV).

MATERIALS AND METHODS

Fifty patients were examined in clinical routine with SPACE (regions of interest: pelvis n=30, lower spine n=12, upper spine n=6, extremities n=4) at 1.5 T. For achieving a high sampling efficiency, parallel imaging, high turbofactor, and magnetization restore pulses were used. In contrast to a conventional TSE imaging technique with constant flip angle refocusing, the refocusing pulse train of the SPACE sequence consists of variable flip angle radiofrequency pulses along the echo train.

RESULTS

Signal-to-noise ratio and contrast-to-noise ratio of SPACE images were of sufficient diagnostic value. The possibility of image reconstruction in multiple planes was of clinical relevance in all cases and simplified data analysis.

CONCLUSION

The achievement of 3-dimensional, T2-weighted TSE magnetic resonance imaging with isotropic and high spatial resolution and interactive 3-dimensional visualization essentially improve the diagnostic potential of magnetic resonance imaging.

Distribution of mesorectal lymph nodes in rectal cancer: in vivo MR imaging compared with histopathological examination. Initial observations

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