Menoufia Medical Journal

ORIGINAL ARTICLE
Year
: 2017  |  Volume : 30  |  Issue : 1  |  Page : 122--127

Preoperative MRI evaluation of mesorectum in cases of rectal carcinoma


Rania A Abd El Samei1, Mohammad S Abdullah2, Mohammad R El-Kholy2,  
1 Department of Radiodiagnosis, Faculty of Medicine, Beni Suef University, Beni Suef, Egypt
2 Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Correspondence Address:
Rania A Abd El Samei
MBBCh, Eslam Street, Bildung Number 408 , 3rd Floor, Beni Suef Governorate, 08604
Egypt

Abstract

Objectives The aim of this study was to evaluate the accuracy of MRI in preoperative staging, in the prediction of negative circumferential resection margin (CRM), and in the planning of surgical management for rectal carcinoma. Background Rectal cancer constitutes about one-third of all gastrointestinal tumors. Preoperative imaging for staging of rectal cancer has become an important aspect of the current approach to rectal cancer management because it helps to select suitable patients for neoadjuvant chemoradiotherapy and determine the appropriate surgical technique. The purpose of this study was to assess the accuracy of MRI in the preoperative staging of rectal carcinoma, in the prediction of negative CRM, and for planning its surgical management. To this end we aimed to study its efficacy in preoperative local staging of rectal carcinoma (T and N stages), in evaluating mesorectal fat and fascia involvement, and in the prediction of negative CRM. Patients and methods Thirty-seven patients with pathologically proven rectal carcinoma underwent pelvic MRI on a 1.5 T magnet with pelvic phased array coil with transrectal gel administration. The MRI protocol was adhered to. All cases were operated upon and their postoperative specimens were compared with preoperative MRI results. Results Comparable to histopathological examination, MRI correctly diagnosed in 34 out of 37 patients in different T stages (accuracy 91.9%) and in 32 out of 37 patients in different N stages (accuracy 86.5%). Accuracy in the evaluation of mesorectal fat invasion was 97.3%, that in the evaluation of mesorectal fascia invasion was 94.5%, and that in the evaluation of CRM was 97.3%. Conclusion MRI of rectal cancer is accurate for preoperative staging, evaluation of mesorectal fat and fascia, prediction of negative CRM, and evaluation of lymph node involvement.



How to cite this article:
Abd El Samei RA, Abdullah MS, El-Kholy MR. Preoperative MRI evaluation of mesorectum in cases of rectal carcinoma.Menoufia Med J 2017;30:122-127


How to cite this URL:
Abd El Samei RA, Abdullah MS, El-Kholy MR. Preoperative MRI evaluation of mesorectum in cases of rectal carcinoma. Menoufia Med J [serial online] 2017 [cited 2020 Apr 9 ];30:122-127
Available from: http://www.mmj.eg.net/text.asp?2017/30/1/122/211484


Full Text



 Introduction



Colorectal cancer ranks third among the most frequently diagnosed tumors in the world, after lung cancer and breast cancer [1]. Recent studies have shown that high-resolution MRI is a reliable and reproducible technique with high specificity (92%) for predicting a negative circumferential resection margin (CRM), the relationship of the tumor to the CRM, and the depth of tumor invasion outside the muscularis propria [2].

High-resolution T2-weighted imaging is the key sequence in the MRI evaluation of preoperative primary rectal cancer. This technique allows differentiation between rectal tumors confined within the rectal wall (stage T2 tumors) and those that extend beyond the muscularis propria (stage T3 tumors) [2].

 Patients and Methods



Seventy-three patients with preoperatively diagnosed rectal cancer were included in this study. The study was performed between March 2014 and May 2015 at the National Cancer Institute in Cairo. Informed consent was obtained from all patients.

Magnetic resonance imaging

Pelvic MRI was performed on a 1.5 T magnet (Philips Acheiva, Guildford Business Park, Guildford, Surrey, United Kingdom) with pelvic phased array coil and rectal gel administration.

The MRI protocol was T1 in the axial plane, T2 in the axial, coronal, and sagittal planes, and T1 postcontrast fat saturation in the axial, coronal, and sagittal planes. Diffusion-weighted MRI was performed for T staging, lymph node staging, evaluation of mesorectal fat invasion, evaluation of mesorectal fascia invasion, and assessment of CRM.

The criteria for MRI interpretation were as follows.

T staging interpretations

T1 was staged if the tumor was confined to the mucosal layer of the rectal wallT2 was staged if there was invasion of the rectal layer up to the muscularis propria, with no penetration of the muscularis propria or perirectal fatT3 was staged if there was invasion of all rectal layers with perirectal fat infiltration yet without pelvic organ involvementT4 was staged if there was invasion of mesorectal fascia and visceral peritoneum or surrounding organ infiltration.

Lymph node staging interpretations

N0 was diagnosed if there was no lymph node metastasisN1 was diagnosed if there was metastasis in one to three lymph nodesN2 was diagnosed if there was metastasis in four or more perirectal lymph nodes.

Mesorectal fat invasion interpretations

Tumor signal intensity extends through the muscle layer into the perirectal fat, with obliteration of the interface between the muscle and perirectal fat.

Mesorectal fascia invasion interpretations

The mesorectal fascia encircles the rectum and the mesorectal fat, nodes, and lymphatic vessels to form a distinct anatomic unit. It is easily identified on axial T2-weighted images as a thin hypointense line. Mesorectal fascia invasion was defined as tumor signal intensity that extends through it into the adjacent structure or viscus.

Circumferential resection margin interpretations

CRM is the distance between the outer margin of the tumor and the mesorectal fascia and is critical for surgical planning, and for determining potential recurrence after total mesorectal excision. An involved CRM was assumed if the shortest distance from either the extramural tumor extension, a suspected lymph node, or a tumor deposit in the mesorectum, to the mesorectal fascia was less than 2 mm. This crucial distance of at least 2 mm can be predicted with 97% confidence when the distance between a tumor and the mesorectal fascia is at least 6 mm on MRI.

MRI sequences interpretations

The coronal T2 displays the relationship between the tumor and the levator muscle, helps to define the region of the anorectal junction, and is important for detecting metastatic iliac nodes, especially in locally advanced rectal cancerThe use of intravenous gadolinium-based contrast agent helps to clarify the relationship between tumor margins and anal sphincters in low-lying rectal cancer and to distinguish tumor infiltration beyond the muscularis proria from penetrating vesselsThe use of fat-suppressed T1-weighted MRI has been advocated to improve visualization of tumor spread into the perirectal fatThe diffusion sequence has important value in the detection of lymph nodes and in differentiation between benign and malignant lymph nodes.

All cases were operated upon usually after 1 month from the last MRI and the postoperative specimens were compared with preoperative MRI results.

All patients had undergone either anterior perineal resection, low anterior resection, or pelvic exenteration according to the location, and extension of previously diagnosed rectal cancer.

Statistical analysis

Data were statistically described in terms of mean ± SD, median and range, or frequencies (number of cases) and percentages when appropriate. Comparison of apparant diffusion coefficient (ADC) between the study groups was done using the Kruskal–Wallis test. Accuracy was represented using the terms sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and overall accuracy. P values less than 0.05 were considered statistically significant. All statistical calculations were done using SPSS (IBM Corporation, Armonk, New York, United States) release 15 for Microsoft Windows (2006).

 Results



The final study consisted of 37 patients. The patients' ages ranged from 20 to 69 years (mean age of 41.9 years). There were 21 (56.8%) men and 16 (43.2%) women.

All 37 patients had preoperative pathologically proven rectal carcinoma of different pathological types; the most common type was adenocarcinoma in 20 (54.1%) patients, as shown in [Table 1].{Table 1}

Rectal tumors were located at different sites of the rectum and were more common at the lower third of the rectum in 25 (67.6%) patients, as shown in [Table 2].{Table 2}

MRI correctly diagnosed in 34 out of 37 patients and the results were comparable to those of histopathological examination at different T stages (accuracy 91.9%).

MRI sensitivity, specificity, PPV, NPV, and accuracy in the differentiation of T2/T3 tumors in correlation to histopathological examination are shown in [Table 3].{Table 3}

MRI sensitivity, specificity, PPV, NPV, and accuracy in the differentiation of T3/T4 tumors in correlation to the histopathological examination are shown in [Table 4].{Table 4}

MRI correctly diagnosed in 32 out of 37 patients and the results were comparable to those of histopathological examination at different N stages (accuracy 86.5%).

MRI sensitivity, specificity, PPV, NPV, and accuracy in the evaluation of lymph node involvement in correlation to the histopathological examination are shown in [Table 5].{Table 5}

MRI sensitivity, specificity, PPV, NPV, and accuracy in the evaluation of mesorectal fat invasion in correlation to the histopathological examination are shown in [Table 6].{Table 6}

MRI sensitivity, specificity, PPV, NPV, and accuracy in the evaluation of mesorectal fascia invasion in correlation to the histopathological examination are shown in [Table 7].{Table 7}

MRI sensitivity, specificity, PPV, NPV, and accuracy in the evaluation of CRM in correlation to the histopathological examination are shown in [Table 8] [Figure 1],[Figure 2],[Figure 3],[Figure 4],[Figure 5].{Table 8}{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}

 Discussion



Colorectal cancer ranks third among the most frequently diagnosed tumors in the world, after lung cancer and breast cancer [3]. About 30–40% of colorectal carcinoma arises from the rectum [1].

The major aim of the present study was to determine the role of MRI in preoperative local staging of colorectal cancer, which is required to predict prognosis and to select the most appropriate management [4].

In our study, the mean age of the patients was 41.9 years, which disagrees with the mean age in the study by Rao et al. [5], who found a mean age of 62 years. This difference might be because their study included a large number of patients (67 patients).

In this study we had found that rectal carcinoma is more common in men (56.8%), which was commensurate with the finding of Zhang et al. [6], in whose study the proportion of men was 60%.

We found that rectal carcinoma is more common at the lower third of the rectum in 67.6% of cases, which agrees with the findings of Akasu et al. [7], who stated that rectal carcinoma is common at the lower third of the rectum in 73.5% of cases.

T staging on MRI was correctly estimated in 34 out of 37 patients (accuracy 91.9%), which agrees with the findings of Zhang et al. [6], who reported an accuracy of 92.1% for MRI for correct diagnosis.

As regards MRI in the differentiation of T2/T3 tumor, the sensitivity and specificity were 100 and 91.6%, respectively, which disagrees with the results of Karatağ et al. [8], who stated that the sensitivity and specificity were 100 and 33.3%, respectively. This difference might be because they did not perform rectal distension and no intravenous or rectal contrast agent was used and hence detection of the infiltration of perirectal fat was difficult.

As regards the efficacy of MRI for the differentiation between T3 and T4 tumor, the sensitivity, specificity, and accuracy were about 85.71, 94.44, and 92%, respectively, which disagrees with the findings of Gagliardi et al. [9], who reported a sensitivity of 89%, specificity of 80%, and accuracy of 86%. This difference may be because of the limited number of patients with T4 lesions (two patients).

As regards the detection of mesorectal fat invasion, the sensitivity, specificity, and overall accuracy were 100, 91.67, and 97.30%, respectively, which was in line with the findings of Akasu et al. [7], who reported sensitivity, specificity, and accuracy of 95, 85, and 91%, respectively.

As regards the detection of mesorectal fascia invasion, the sensitivity, specificity, and overall accuracy were 85.71, 96.71, and 94.59%, respectively, which agrees with the results of Rao et al. [5], who stated that the overall accuracy was 88% and sensitivity and specificity were 80 and 90.4%, respectively.

As regards the assessment of CRM status, the sensitivity, specificity, and overall accuracy were 91.67, 100, and 97.30%, respectively, which agrees with the findings of Iannicelli et al. [10], who reported sensitivity, specificity, and overall accuracy of 89.5, 96.3, and 94.5%, respectively.

As regards the assessment of lymph nodes, the sensitivity, specificity, and accuracy were 88.89, 94.74, and 91.89%, respectively, which disagrees with the findings of Zhang et al. [6], who stated that sensitivity, specificity, and accuracy were 64.7, 90.5, and 79%, respectively. This difference might be due to the fact that in our study we depended mainly on morphological criteria of the lymph nodes, diffusion pattern, and its ADC value and considering the lymph node size significant even if it only up to 5 mm.

Recently, it was reported that nodal margins and internal nodal characteristics are the most reliable indicators of malignancy.

Features that are suggestive of malignancy include irregular or speculated nodal margins and heterogenous signal intensity, in addition to the restricted diffusion pattern of the involved node. The evaluation of these features requires high-resolution images that cover all nodes of importance, including superior rectal and pelvic sidewall adenopathy [6].

 Conclusion



In our study we concluded that MRI is a highly accurate noninvasive diagnostic modality for preoperative local staging of rectal carcinoma (T and N stages) as well as for determining the extent of mesorectal fascia involvement.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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