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

Preoperative MRI evaluation of mesorectum in cases of rectal carcinoma


1 Department of Radiodiagnosis, Faculty of Medicine, Beni Suef University, Beni Suef, Egypt
2 Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt

Date of Submission27-Mar-2016
Date of Acceptance27-Jun-2016
Date of Web Publication25-Jul-2017

Correspondence Address:
Rania A Abd El Samei
MBBCh, Eslam Street, Bildung Number 408 , 3rd Floor, Beni Suef Governorate, 08604
Egypt
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/1110-2098.211484

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  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.

Keywords: circumferential resection margin, high-resolution magnetic resonance imaging, mesorectum, rectal cancer


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;30:122-7

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 2019 Aug 25];30:122-7. Available from: http://www.mmj.eg.net/text.asp?2017/30/1/122/211484




  Introduction Top


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 Top


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 wall
  • T2 was staged if there was invasion of the rectal layer up to the muscularis propria, with no penetration of the muscularis propria or perirectal fat
  • T3 was staged if there was invasion of all rectal layers with perirectal fat infiltration yet without pelvic organ involvement
  • T4 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 metastasis
  • N1 was diagnosed if there was metastasis in one to three lymph nodes
  • N2 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 cancer
  • The 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 vessels
  • The use of fat-suppressed T1-weighted MRI has been advocated to improve visualization of tumor spread into the perirectal fat
  • The 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 Top


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 Number of the lesions and percentage of different pathological lesions

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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 Location of the rectal lesions and number of cases at the affected site

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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 Magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the differentiation of T2/T3 tumors in correlation to histopathological examination

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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 Magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the differentiation of T3/T4 tumors in correlation to histopathological examination

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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 Showed magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the evaluation of lymph node involvement in correlation to histopathological examination

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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 Magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the evaluation of mesorectal fat invasion in correlation to histopathological examination

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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 Magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the evaluation of mesorectal fascia invasion in correlation to histopathological examination

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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 Magnetic resonance imaging sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in the evaluation of circumferential resection margin in correlation to histopathological examination

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Figure 1: Male patient aged 34 years with adenocarcinoma grade II, staged T4 N1. MRI of (a) sagittal T2 and (b) axial T2 revealed rectal neoplastic mural thickening involving the mid and lower rectum (red arrowhead in a). It is seen extending into the mesorectal fascia anteriorly (blue arrowhead in b).

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Figure 2: Female patient aged 67 years with adenocarcinoma grade II, staged T2 N0. MRI of (a and b) sagittal T2 and axial T1 showing mass involving the lower one-third of the rectum and anorectal junction (red arrowhead in a). It is seen infiltrating the submucosa and the muscularis propria of the rectal wall with no extra serosal extension and intact mesorectal fat and fascia (blue arrow in b).

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Figure 3: Male patient aged 28 years with signet ring cell carcinoma, staged T3 N2. MRI of (a-c) sagittal T2, axial T2, diffusion showing long segment of mural tumefaction with subsequent luminal compromise (red arrowhead in a) and smudging of the fat planes within the mesorectum more evidently on the right side (blue arrowhead in b). It is seen associated with a few small mesorectal lymph nodes showing restricted diffusion (red arrow in c).

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Figure 4: Male patient aged 47 years with villous adenocarcinoma, staged T4 N0. MRI of (a) sagittal T2 and (b and c) axial T2 showing rectal neoplastic soft tissue thickening having exophytic necrotic soft tissue mass from the anterior rectal wall (blue arrowhead in b). It is seen infiltrating the seminal vesicles as well as the urinary bladder wall (blue arrowhead in c) with large rectovesical large fistulous communication (red arrow in a). No sizable perirectal lymph nodes.

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Figure 5: A 46-year-old female patient with mucinous adenocarcinoma, staged T3 N0. MRI of. (a) sagittal T2, (b and c) axial. T1, and axial T1 postcontrast fat saturation showing irregular mural tumefaction starting with cranial extension. (red arrowhead in a). The lesion involved the full thickness of the rectum together with loss of serosal outline definition and anterior extension of the tumefaction into the mesorectum fat planes and reaching as far as its anterior limit. (blue arrow in b). The nearby ileal loops appear amalgamated with loss of the mesenteric fat planes. (blue arrow in c).

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  Discussion Top


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 Top


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.



 
  References Top

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Akasu T, Iinuma G, Fujita T, Muramatsu Y, Tateishi U, Miyakawa K, et al. Thin-section MRI with a phased-array coil for preoperative evaluation of pelvic anatomy and tumor extent in patients with rectal cancer. Am J Roentgenol 2005; 184:531–538.  Back to cited text no. 7
    
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Karatağ O, Karatağ GY, Özkurt H, Değirmenci HK, Avlanmış Ö, Başak M, Baykan A. The ability of phased-array MRI in preoperative staging of primary rectal cancer: correlation with histopathological results. Diagn Interv Radiol 2012; 18:20–26.  Back to cited text no. 8
    
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Gagliardi G, Bayar S, Smith R, Salem RR. Preoperative staging of rectal cancer using magnetic resonance imaging with external phase-arrayed coils. Arch Surg 2002; 137:447–451.  Back to cited text no. 9
    
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Iannicelli E, di Renzo S, Ferri M, Pilozzi E, di Girolamo M, Sapori A, et al. Accuracy of high-resolution MRI with lumen distention in rectal cancer staging and circumferential margin involvement prediction. Korean J Radiol 2014; 15:37–44.  Back to cited text no. 10
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8]



 

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