Staging Of Rectal Cancer Research Articles

Design of Microchannel Induced Cantilever Sensor to Detect the Rectal Cancer

Rectal cancer is the third most cause of cancer deaths. In the year 2020, 53,200 patients suffering from rectal cancer will die out of 1,47,950 patients who have undergone diagnosis according to the national center for health statistics. Even though the incident and mortality rates are shown as decreasing as per these statistics from 1970 to 2020 but the population rate is increased during the same period. According to statistics 3,640 patients whose age is below 50 years also will die. We have observed that there is an increase in the number of patients with rectal cancer. This is due to costly screening tests for rectal cancer. We propose a MEMS (micro electro mechanical system) based biosensor to detect and estimate the rectal cancer stages. This study also includes an array of cantilevers consisting of a microfluidic channel. These micro channels are coated with antibodies to recognize the stages of rectal cancer.

Impact of Treatment Coordination on Overall Survival in Rectal Cancer

BackgroundRectal cancer treatment is often multimodal, comprising of surgery, chemotherapy, and radiotherapy. However, the impact of coordination between these modalities is currently unknown. We aimed to assess whether delivery of nonsurgical therapy within same facility as surgery impacts survival in patients with rectal cancer. MethodsA patient cohort with rectal cancer stages II to IV who received multimodal treatment between 2004 and 2016 from National Cancer Database was retrospectively analyzed. Patients were categorized into three groups: (A) surgery + chemotherapy + radiotherapy at same facility (surgery + 2); (B) surgery + chemotherapy or radiotherapy at same facility (surgery + 1); or (C) only surgery at reporting facility (chemotherapy + radiotherapy elsewhere; surgery + 0). The primary outcome was 5-year overall survival (OS), analyzed using Kaplan-Meier curves, log-rank tests, and Cox proportional-hazards models. ResultsA total of 44,716 patients (16,985 [37.98%] surgery + 2, 12,317 [27.54%] surgery + 1, and 15,414 [34.47%] surgery + 0) were included. In univariate analysis, we observed that surgery+2 patients had significantly greater 5-year OS compared to surgery + 1 or surgery + 0 patients (5-year OS: 63.46% vs 62.50% vs 61.41%, respectively; P= .002). We observed similar results in multivariable Cox proportional-hazards analysis, with surgery + 0 group demonstrating increased hazard of mortality when compared to surgery + 2 group (HR: 1.09; P< .001). These results held true after stratification by stage for stage II (HR 1.10; P= .022) and stage III (HR 1.12; P< .001) but not for stage IV (P= .474). ConclusionGreater degree of care coordination within the same facility is associated with greater OS in patients with stage II to III rectal cancer. This finding illustrates the importance of interdisciplinary collaboration in multimodal rectal cancer therapy.

Oncologic Outcomes Associated With MRI-detected Extramural Venous Invasion (mrEMVI) in Rectal Cancer: A Systematic Review and Meta-analysis.

The role of MRI-detected EMVI (mrEMVI) as a reliable prognostic factor in rectal cancer has been emphasized in recent years but this finding remains underreported by many institutions. This review aimed to demonstrate the importance of pre- and post-treatment MRI-detected EMVI as independent prognostic factors of adverse oncologic outcomes in patients undergoing neoadjuvant therapy followed by total mesorectal excision. This review was designed using the PRISMA guidelines. The following electronic databases were searched from January 2002 to January 2020: CENTRAL, Ovid MEDLINE, PubMed, and Ovid Embase. Main outcomes included DFS and overall survival (OS). Other outcomes of interest comprised positive resection margin and synchronous metastases. Seventeen studies involving a total of 3821 patients were included for data synthesis. For preneoadjuvant treatment mrEMVI, pooled hazard ratio (HR) estimate for DFS was 2.30 (95% confidence intervals (CI) 1.54-3.44) for higher recurrence in mrEMVI-positive patients. mrEMVI-positive patients were found to have a lower OS with a pooled HR of 1.68 (95%CI 1.27-2.22). Pooled risk ratio for synchronous metastasis was 4.11 (95%CI 2.80-6.02) for mrEMVI-positivity. For postneoadjuvant treatment EMVI (ymrEMVI), positive status showed a lower DFS with a pooled HR of 2.04 (95%CI 1.55-2.69). Risk ratio of having a positive resection margin status was 2.95 (95%CI 1.75-4.98) for ymrEMVI-positive patients. This review showed that oncologic outcomes are significantly worse for both pre- and post-neoadjuvant treatment mrEMVI-positive patients. MRI-detected EMVI should be consistently reported in rectal cancer staging and may provide guidance for the targeted use of additional systemic therapy.

SURVIVAL OF PATIENTS WITH RECTAL CANCER

The aim: To evaluate the early and late results of treatment of rectal cancer patients after special treatment methods with a view to indentifying optimal method of treatment in correlation with the stage of the disease. Materials and methods: The study is based on the results of observation of 779 patients with stage II, III and IV rectal cancer (RC) who were divided into groups according to the treatment (surgery, surgery + chemotherapy, chemotherapy, surgery + chemotherapy + radiation therapy, radiation therapy + surgery, radiation therapy). Results: According to the results obtained, the overall survival of patients correlates with the stage of rectal cancer: we see the highest percentage of patients’ survival in stage II and, accordingly, the lowest – in stage IV in each of the studied time intervals. Conclusions: The use of combined and integrated treatment in patients with stages II and stage III and the use of chemotherapy in stage IV RC gives a higher rate of cumulative survival of patients at each of the studied intervals

Transanal Endoscopic Microsurgery (TEMS) for Rectal Cancer: Patient Decision-making, Postoperative Experience and Quality of Life.

Transanal endoscopic microsurgery (TEMS) is a form of minimally invasive surgery for selected rectal cancers. The aim of this study was to explore the factors affecting patients' decision-making concerning the choice of surgical treatment as well as to measure the Quality of Life (QoL) post-TEMS. Thirty-four patients with rectal cancer stage T1/T2-N0-M0 that underwent TEMS were studied. The questionnaires used included the Short Form SF12v2, Wexner Score (CCF-FIS) and the Sexual Function Questionnaire (SFQ). The patients' views on experience and treatment decision were obtained with a custom-designed questionnaire. Questionnaires were completed at a mean of 6.9 years following treatment. The factors that influenced the patients' decisions were: experience satisfaction (p=0.003), postoperative bowel function (p<0.001), lower incontinence score (p=0.020) and agreement of TEMS experience with preoperative information (p=0.049). Treatment experience satisfaction was associated with family support (p=0.034) and agreement with preoperative information (p=0.047), better bowel function (p=0.026) and mental QoL (MCS) (p=0.003). factors important to patients when reflecting on treatment experience are adequate and reliable information, a good QoL and the presence of family support. Clinicians should incorporate those parameters in their practice when assisting patients in making a surgical treatment choice and provide informed consent on TEMS for rectal cancer.

Role of Magnetic Resonance Imaging in Defining Rectal Anatomical Landmarks and Primary Rectal Cancer Evaluation

In contemporary practice, magnetic resonance imaging (MRI) has become a useful tool in evaluating rectal and perirectal anatomy. It encourages accurate local staging of rectal cancer and has overall improved presurgical evaluation and planning, leading to reduce local recurrence and more sphincter conserving procedures. This article aims at providing a concise review of rectal MRI technique and anatomy and to relate this to local staging and surgical management. Locally generated images in our practice were reviewed and images that best depict different anatomical landmarks and pathologies were selected and presented. Also, PubMed database was searched for relevant and contemporary existing literature on the subject.

MRI-Pathology Agreement in Rectal Cancer: Real-World Data from a Prospective Rectal Cancer Registry.

Introduction: Magnetic Resonance Imaging (MRI) is routinely used in preoperative rectal cancer staging. The concordance of MRI staging with final pathologic exam, albeit improved, has not yet reached perfection. The aim of this study is to analyze the agreement between MRI and pathologic exam in patients operated on for mid-low rectal cancer. Material and Method: Patients undergoing neoadjuvant chemoradiation therapy (nCRT) or upfront surgery were analyzed. Between January 2019 to December 2019, 140 patients enrolled in the AIMS Academy rectal cancer registry were analyzed. Sixty-two patients received nCRT and 78 underwent upfront surgery. Results: Overall, the agreement between MRI and pathologic exam on T stage and N stage were 64.7% and 69.2%, respectively. The agreement between MRI and pathologic exam on T stage was 62.7% for patients who did not receive nCRT and 67.4% for patients who received nCRT (p = 0.62). The agreement on N stage was 76.3% for patients who did not receive nCRT and 60.0% for patients who received nCRT (p = 0.075). Conclusions: Real-world data shows MRI is still far from being able to correlate with the pathology findings which raises questions about the accuracy of the real-life decision-making process during cancer boards.

Risk factors associated with non-closure of defunctioning stoma in patients with rectal cancer: univariate and multivariate analysis

To identify the risk factors associated with non-closure of defunctioning stoma in patients with rectal cancer. A retrospective analysis included patients who underwent surgical treatment at the Ryzhikh National Medical Research Centre of Coloproctology for the period from March 2017 to August 2019. Inclusion criterion was anterior or low anterior resection followed by anastomosis and preventive stoma. Univariate and multivariate analysis enrolled 28 factors for identifying the risk factors of non-closure of defunctioning stoma. There were 246 patients with rectal cancer. Intraoperative fluorescence angiography was applied in 145 cases to assess blood supply within the anastomosis and reduce the risk of anastomotic leakage. According to multivariate analysis, only two factors had significant influence on non-closure of preventive stoma - any grade of anastomotic leakage (OR 6.5; 95% CI 2.2-18.8, p=0.001) and rectal cancer stage IV (OR 7.2; 95% CI 1.9-27.6, p=0.004). According to our data, permanent stoma is observed in 15% of patients.

Role of positron emission tomography/computed tomography for the staging of primary colorectal cancers

ObjectiveThe aim of this paper was to evaluate the role of positron emission tomography (PET) combined with contrast-enhanced computed tomography (CECT) in staging patients with primary colorectal cancer (CRC).BackgroundCRC is the second leading cause of cancer-related deaths and the fourth most common malignancy worldwide. Cross-sectional imaging studies such as CT and MRI have evolved as the best modalities for staging rectal cancer. PET combined with CT is widely used not only for preoperative staging, but also for assessing the outcomes of rectal carcinoma.Patients and methodsThis prospective study was carried out on 50 patients: 30 (60%) men and 20 (40%) women in the age range from 27 to 74 years, who were diagnosed or suspected to have cancer colon by other radiological imaging.ResultsOur results showed that PET-CT had equal sensitivity (95.4%) and specificity (82%), positive predictive value (PPV) (80.7%), negative predictive value (NPV) (95.8%), and accuracy (88%) for the detection of regional lymph node metastasis compared to CECT. But PET-CT and CECT had higher sensitivity and higher specificity, PPV, NPV, and accuracy more than PET for detection of metastatic lymph nodes and PET-CT had equal sensitivity (92.8%) and specificity (86.2%), PPV (72.2%), NPV (96.8%), and accuracy (88%) for detection of lung metastasis compared to PET. But PET-CT and PET had higher sensitivity and higher specificity, PPV, NPV, and accuracy more than CECT for detection of pulmonary deposits.ConclusionAccording to our results, fluorine-18 fluorodeoxyglucose PET/CT has contributed positively to the staging of primary CRC patients.

Better prognostic determination of cT3 rectal cancer through measurement of distance to mesorectal fascia: A multicenter study.

ObjectiveTo forward the magnetic resonance imaging (MRI) based distance between the deepest tumor invasion and mesorectal fascia (DMRF), and to explore its prognosis differentiation value in cT3 stage rectal cancer with comparison of cT3 substage.MethodsThis was a retrospective, multicenter cohort study including cT3 rectal cancer patients undergoing neoadjuvant chemoradiotherapy followed by radical surgery from January 2013 to September 2014. DMRF and cT3 substage were evaluated from baseline MRI. The cutoff of DMRF was determined by disease progression. Multivariate cox regression was used to test the prognostic values of baseline variables.ResultsA total of 804 patients were included, of which 226 (28.1%) developed progression. A DMRF cutoff of 7 mm was chosen. DMRF category, the clock position of the deepest position of tumor invasion (CDTI) and extramural venous invasion (EMVI) were independent predictors for disease progression, and hazard ratios (HRs) were 0.26 [95% confidence interval (95% CI), 0.13−0.56], 1.88 (95% CI, 1.33−2.65) and 1.57 (95% CI, 1.13−2.18), respectively. cT3 substage was not a predictor for disease progression.ConclusionsThe measurement of DMRF value on baseline MRI can better distinguish cT3 rectal cancer prognosis rather than cT3 substage, and was recommended in clinical evaluation.

Semiotics and the role of transrectal ultrasound in rectal cancer staging

Transrectal ultrasound (TRUS) is inexpensive and simple method for examining the rectum and surrounding tissues. In particular it is used to preoperatively assess stage, in patients with rectal cancer. By using TRUS is possible to analyze the neoplasm extent, depth of tumor invasion into the layers of the colon wall, the mesorectal lymph node involvement and the circumferential resection margin. This method is comparable to an expensive magnetic resonance imaging scan, and if done correctly could even exceed it. The correct diagnosis, especially in the early stages of the disease, plays an important role in choosing surgical treatment in future. However, to interpret the results, you must be familiar with the anatomy of the rectum and anal canal, as well as follow the simple rules for the preparation and implementation of TRUS. If you follow all the rules, you can answer the question about the possibility of performing organ-preserving surgery and compliance with cancer radicalism.

The Role of Diffusion MRI in Rectum Cancer Staging and Evaluation of Neoadjuvan Treatment Efficiency

The correct staging of rectal cancer is very important for treatment. This study aims to show the contribution of diffusion-weighted imaging (DWI) to staging, to predict tumor differentiation and neoadjuvant chemoradiotherapy response using DWI. The study con- sisted of 36 patients and 22 control groups. 12 patients who received neoadjuvant therapy were evaluated before and after treatment. Magnetic Resonance Imaging (MRI) and DWI were performed to all patients and apparent diffusion coefficient (ADC) maps were obtained. The findings were compared with histopathological results. T staging accuracy was 72.2% on MRI. N staging accuracy rate was 75% on the T2 sequence and 72.2% on DWI. Tumoral rectal ADC values were significantly decreased compared to the normal rectal wall (p&lt; 0.001). Mean T3 and T4 (extramural) ADC values were significantly decreased compared to the T2 stage (intramural) ADC values (p&lt; 0.001). ADC and relative ADC (lymph node / primary tumor ADC) values of the metastatic lymph nodes were signifi- cantly decreased compared to benign lymph nodes (p&lt; 0.001). According to the ADC cut point, N staging accuracy was found to be 83%. The ADC values of the low differentiated group were significantly decreased compared to the moderately and well-differentiated group (p&lt; 0.011). In the control MRI of patients receiving neoadjuvant therapy, the ADC increase in the group that responded well to the treatment was significantly higher than the group with partial response (p &lt;0.004). As a result, DWI and ADC are useful for preoperative rectum cancer evaluation. Keywords: Rectum cancer, Staging, Diffusion MRI

Accuracy of pelvic magnetic resonance imaging in local staging for rectal cancer: a single local health district, real world experience.

Neoadjuvant chemoradiotherapy plays a key role in reducing local recurrence rates for locally advanced rectal cancer. Pelvic magnetic resonance imaging (pMRI) is the gold standard for local clinical staging which allows clinicians to decide the treatment patients receive. A more advanced tumour or the presence of high-risk features on pMRI mean that neoadjuvant therapy will be offered to these patients. Understanding the accuracy of pMRI in local staging for rectal cancer is therefore crucial. A retrospective cohort analysis of the accuracy of pMRI staging in a subgroup of patients who had primary rectal cancer surgery without neoadjuvant therapy was performed. Specificity and sensitivity for T-staging, N-staging and presence of high-risk features (threatened circumferential resection margin and extramural venous invasion) were calculated. Patients who had previous pelvic surgery, previous pelvic radiotherapy and previous surgery for continence were excluded. A total of 114 patients were included in the analysis. MRI accurately predicts T-stage in 56.6% and N-stage in 55.8%. Prediction of extramural disease was accurate in 51%. A negative circumferential resection margin was accurately predicted in 98.6% of patients. Overall adherence to reporting proforma was 15.8%. Overall, this study provided valuable information about the clinical staging of patients with rectal cancer who are at an early stage within a large regional catchment area in Australia with pMRI. These results allow us to assess the accuracy of our local staging with ramifications to the clinical decisions being made in the context of the more recent trials which questioned the need for neoadjuvant chemo-radiotherapy in all node positive patients.

Preoperative concurrent chemoradiotherapy MRI characteristics favouring pathologic complete response in patients with rectal cancer: Usefulness of MR T2-stage as an ancillary finding for predicting pathologic complete response.

This study sought to assess preoperative concurrent chemoradiotherapy (CRT) magnetic resonance imaging (MRI)-based findings according to a structured MRI report template for primary staging of rectal cancer, and to evaluate the prognostic relevance of the pre-CRT MRI-based findings in patients with rectal cancer after CRT. We retrospectively evaluated pre- and post-CRT MRI data of patients with pathologically proven rectal adenocarcinoma, between January 2008 and October 2019. Image interpretation was performed independently by two radiologists and each reviewer assessed the cancer characteristics on MRI, based on the structured MRI report for primary staging. MRI-based findings associated with pathologic complete tumour regression grade (TRG) after CRT were analysed by univariate and multivariate analysis. Significant factors from pre-CRT MRI were weighted to score mrTRG in post-CRT MRI. On univariate analysis, MR T-stage, tumour infiltration, mesorectal fascia involvement, extramural vascular invasion and serum carcinoembryonic antigen level correlated significantly with pathologic complete response (pCR). Multivariate analysis identified that only MR T-stage was independently associated with pCR (odds ratio, 3.89, 95% confidence interval, 1.18-12.84; P=0.0278). Adding MRI-based T2-stage as an ancillary finding to mrTRG statistically significantly improved the sensitivity as compared to using only mrTRG for considering a CR. T2_mrTRG was significantly different in terms of the time to tumour progression between the CR and non-CR group. The MR T2-stage was independently associated with pCR after CRT in patients with rectal cancer and was helpful as ancillary predictive factor, adding to mrTRG for prediction of pCR.

Application value of endoscopic ultrasonography combined with enhanced MRI in preoperative staging of rectal cancer

Application value of endoscopic ultrasonography combined with enhanced MRI in preoperative staging of rectal cancer

Role of imaging and synoptic MRI reporting in determining optimal management paradigm for rectal cancer: a narrative review

: Magnetic resonance imaging plays a key role in the primary staging and post-treatment assessment of rectal cancer. MRI with high resolution T2-weighted sequences accurately assesses tumour morphology, location, depth of spread and the relationship of the tumour to surrounding structures such as the circumferential resection margin. The extent of disease beyond the mesorectal plane is well defined by MRI. In addition, MRI identifies poor prognostic indicators such as tumour deposits and extramural venous invasion. The information gleaned from the MRI assists the multidisciplinary team to determine the most appropriate treatment including surgical planning, mapping for radiotherapy treatment and the decision to administer neoadjuvant chemotherapy. Systematic proforma reporting of rectal MRI by radiologists is based on a template containing a comprehensive list of diagnostic and prognostic information. This form of reporting is encouraged as it provides consistency in radiology reporting and enables clinicians to communicate effectively with patients about the treatment pathways they will undertake. Clarity at diagnosis is critical for developing treatment plans that will produce optimal patient outcomes. MRI is also useful in restaging of rectal tumours post neoadjuvant chemotherapy and may assist in the detection of local recurrence. In this review, the role and accuracy of MRI in the local staging of rectal cancer both at baseline and after neoadjuvant treatment, the ideal MR imaging protocol and the benefits of proforma reporting will be discussed.

Clinical staging accuracy and the use of neoadjuvant chemoradiotherapy for cT3N0 rectal cancer: Propensity score matched National Cancer Database analysis

BackgroundWhile neoadjuvant chemoradiation therapy (nCRT) is accepted as standard of care for locally advanced rectal cancer, the approach to treatment of patients with clinically staged T3N0 disease has been increasingly debated. This study examines the accuracy of clinical staging for cT3N0 rectal cancer as recorded in the National Cancer Data Base and evaluates the role of nCRT in treating these patients. MethodsTotal of 15,843 patients with clinically staged T3N0M0 rectal cancer who either received nCRT or proceeded to surgery-first met inclusion criteria. Propensity score matching was employed to balance the groups. Results23% of cT3N0 patients undergoing surgery-first were found to have pathologically positive nodes. Another 16% turned out to have < stage II disease on surgical pathology. Survival curves for matched nCRT and surgery-first groups demonstrated a survival advantage for cT3N0 patients treated with nCRT. ConclusionsPoor clinical staging accuracy can result in both undertreatment and overtreatment of cT3N0 rectal cancer.

Superior Mesenteric and Inferior Mesenteric Artery Diameters in Colorectal Cancer.

To compare the superior mesenteric artery (SMA) and inferior mesenteric artery (IMA) diameters in colorectal cancer compared to control. Observational study. Taizhou Hospital, Zhejiang University, Taizhou, China, from March 2019 to June 2020. A total of 203 diagnosed colorectal cancer patients and 40 patients as control subjects were reviewed. Patients were divided into three groups based on tumor location as the right colon, left colon, and rectal groups. The diameters were measured on axial computed tomography images independently by two observers. The SMA diameter did not differ between the right colon and control groups (p=0.626). The IMA diameter was significantly higher in the left colon group than in the control group (p=0.002), but there was no significant difference in the IMA diameter between the different tumour stages (p=0.263). The IMA diameter was significantly higher in the rectal group than in the control group (p<0.001). There was a significant increase in the IMA diameter from stage I to stage II rectal cancers (p=0.022) and from stage II to stage III rectal cancers (p=0.003). The IMA diameter did not differ between stage III and IV rectal cancers (p=0.600). In locoregional rectal cancer patients, there was a significant correlation between the IMA diameter and tumour-node-metastasis stage (p<0.001, rs = 0.494). Patients with rectal cancer and left colon cancer have a wider IMA diameter than patients without colorectal cancer. IMA diameter can be a potential marker for locoregional staging of rectal cancer. Key Words: Superior mesenteric artery, Inferior mesenteric artery, Colorectal cancer, Markers, Diameter.

Imaging Strategies for Rectal Cancer Initial Staging: Does Pelvic Computed Tomography Provide Significantly Additional Findings when High-resolution Magnetic Resonance Imaging has Been Performed?

Initial staging of rectal cancer is done by high-resolution magnetic resonance imaging (MRI), however, pelvic computed tomography (CT) is also frequently used. The aim of this study was to evaluate the added clinical benefit of pelvic CT or whether it can alter the initial staging or not. The study was composed of 187 patients with rectal cancer. Firstly, imaging except pelvic CT was evaluated. Secondly, the pelvic CT was evaluated and the staging was adjusted according to the new findings. Subsequently, the two staging results were compared to investigate the added clinical benefit of pelvic CT. Compared with the imaging data except pelvic CT, new findings revealed by the pelvic CT included metastases of the pelvic bone (n = 1) and pelvic peritoneum (n = 3). However, the new findings did not change the primary staging. Of the three patients with pelvic peritoneal metastasis, two were already determined with peritoneal involvement and ascites by abdominal CT, and the third patient was observed with liver and distant lymph node metastasis. Thus, none of their initial stagings needed to be changed. The addition of pelvic CT to the pre-treatment imaging strategy cannot provide added clinical benefit for the primary evaluation of rectal cancer.

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

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. 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. PET/MR outperformed MR in evaluating tumor size (42.5 ± 21.03mm per the reference standard, 54 ± 20.45mm by stand-alone MR, and 44 ± 20mm 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. 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.