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Year : 2014  |  Volume : 51  |  Issue : 2  |  Page : 170--175

Pre-operative staging of rectal cancer using multi-detector row computed tomography with multiplanar reformations: Single center experience

RA Dar1, NA Chowdri1, FQ Parray1, F Shaheen2, SH Wani3, M Mushtaque1,  
1 Department of General and Minimal Invasive Surgery, Sher-i-Kashmir Institute of Medical Sciences, Soura, India
2 Department of Radiodiagnosis and Imaging, Sher-i-Kashmir Institute of Medical Sciences, Soura, India
3 Department of General Surgery, Government Medical College, Srinagar, Jammu and Kashmir, India

Correspondence Address:
R A Dar
Department of General and Minimal Invasive Surgery, Sher-i-Kashmir Institute of Medical Sciences, Soura
India

Abstract

Background: Technical advancement in imaging has helped to stage and plan treatment modality for carcinoma rectum with still some objectives controversial. Aims: The aim of our study was to evaluate the accuracy of multidetector row computed tomography (MDCT) with multiplanar reformations in the pre-operative staging of rectal carcinoma and correlation with intraoperative and histopathologic staging of retrieved specimen with respect to the depth of tumor invasion (T-staging), lymph node metastasis (N-staging) and mesorectal fascia (MRF) involvement. Materials and Methods: The study was a prospective one and consisted of 52 patients with biopsy proved rectal carcinoma. MDCT studies were performed on a 64-slice computed tomography system. Images were reconstructed in axial, coronal and sagittal planes. MDCT findings were compared with intraoperative and pathologic (reference standard) findings. Sensitivity, specificity, positive predictive value, negative predictive value and accuracy were assessed. Results: The diagnostic accuracy of MDCT for T1/T2, T3 and T4 lesions was 77%, 86.5% and 100%, respectively. For perirectal lymph node metastasis (N+), the diagnostic accuracy of MDCT was 84.1%. The diagnostic accuracy of MDCT for MRF involvement was 91%. Conclusion: MDCT is a reliable radiological tool for local staging of rectal cancer with excellent accuracy rates for T and N-staging of rectal cancer.



How to cite this article:
Dar R A, Chowdri N A, Parray F Q, Shaheen F, Wani S H, Mushtaque M. Pre-operative staging of rectal cancer using multi-detector row computed tomography with multiplanar reformations: Single center experience.Indian J Cancer 2014;51:170-175


How to cite this URL:
Dar R A, Chowdri N A, Parray F Q, Shaheen F, Wani S H, Mushtaque M. Pre-operative staging of rectal cancer using multi-detector row computed tomography with multiplanar reformations: Single center experience. Indian J Cancer [serial online] 2014 [cited 2020 Nov 24 ];51:170-175
Available from: https://www.indianjcancer.com/text.asp?2014/51/2/170/138292


Full Text

 Introduction



Rectal cancer is one of the most common malignant tumors of the gastrointestinal tract, [1] comprising 30% of all colorectal cancers. In the developed countries, it is the second most common tumor after lung cancer. Over the past 20 years, many improvements have been made in the surgical, radiologic and oncologic treatment of rectal cancer. However, this neoplasm continues to have a highly variable outcome and is associated with a poor prognosis owing to the high risk of metastasis and local recurrence. Local recurrence rates for rectal cancer, after surgical treatment, vary from 3% to 32%. [2],[3],[4],[5],[6] The success of tumor excision depends largely upon accurate tumor staging and appropriate surgical technique. Staging rectal tumor is crucial for the prognosis and planning of therapy in the individual patient and aims at precisely determining the extent of the tumor as a basis for deciding whether surgery alone or surgery in combination with neoadjuvant therapy is the most suitable strategy. Various modalities exist at present, for the pre-operative staging of rectal cancer including endorectal ultrasonography (EUS), computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography.

EUS is mostly accurate both in the evaluation of early stages (T1 and T2) and in demonstrating the perirectal spread of tumor (T3 tumors); however, it has several limitations: Operator dependency, limitation to tumors located in the upper rectum when a rigid probe is used; no assessment of stenotic tumors and inability to visualize the mesorectal fascia (MRF). [7],[8] EUS also shows low sensitivity in detecting perirectal lymph node metastasis and low accuracy in evaluating the patients who had previously received neoadjuvant chemo/radiotherapy.

Although CT was the first technique introduced, it has limitations in differentiating and distinguishing different layers of the rectal wall and has overall lower accuracy than EUS and MRI. The accuracy has since been improved by the advent of the multidetector row computed tomography (MDCT), with reconstructions in multiplanar reformations (MPR's). The introduction of MDCT allowed thin collimation scanning, resulting in improved MPRs. These benefits may help to establish MDCT as an effective diagnostic technique in the evaluation of pre-operative local staging of rectal cancer. With the introduction of MDCT with isotropic resolution, the diagnostic capability of MDCT has markedly improved and the benefits are to be expected in staging of rectal carcinoma. At present, only a few MDCT studies have been published on the subject of rectal cancer staging.

Rectal cancer is common in our valley and our institute, being a tertiary care center, is a high volume center for these cancers. Hence, we thought it worthwhile to study the role of MDCT in the pre-operative evaluation of rectal cancer.

The aim of our study was to evaluate the accuracy of MDCT in pre-operative staging of rectal cancers and correlation with intraoperative and histopathologic staging of resected specimen with respect to: T-staging, N-staging, MRF involvement and M-staging.

 Materials and Methods



The study was a prospective one conducted from May-2008 to March-2011 in the Department of General Surgery of our institute, in collaboration with Departments of Radiodiagnosis and Pathology.

Institutional approval was obtained for this prospective study. The study population consisted of 52 patients (28 women and 24 men) with histopathologically proved rectal cancer by means of endoluminal biopsy. Rectal cancer was defined as carcinoma within 15 centimeter of the anal verge. The initial diagnosis was made at digital rectal examination/proctoscopy/sigmoidoscopy and all patients were subjected to colonoscopy to detect synchronous lesions. Written informed consent was obtained from all patients for these diagnostic procedures.

The mean age of the patients was 51 years, with a range of 17-80 years. All MDCT studies were performed on a 64-Slice CT system (Sensation 64, Siemens, Forchiem, Germany). The scan protocol comprised a slice collimation of 64 mm × 0.6 mm, table feed/rotation: 15.0 mm, rotation time 0.5 s. and reconstruction increment of 5 mm. Each scan was obtained with a tube voltage of 120 kV and 180-250 mAs, depending on the patient's weight. All patients received 15 ml of oral contrast (sodium diatrizoate) dissolved in 1 L of water, 2-3 h prior to scanning. Then, on table, patients received 100 ml of non-ionic IV contrast agent (iohexol) at a flow rate of 3 ml/s and imaging was performed 60 s after the start of the injection. No rectal contrast media or air insufflation was used before imaging. Examinations were performed during one breath-hold from the level of the diaphragm to the anal verge.

Images were reconstructed in axial, coronal and sagittal planes from the raw data for interactive multiplanar image viewing on a work-station and for documentation on axial planes for the surgeon. MDCT scans were then assessed for detectability of the tumor, location and depth of tumor infiltration, MRF involvement and regional lymph node involvement. Tumors on MDCT were classified by a modified Tumor, Nodes, Metastasis TNM stage: Tumor confined to the bowel wall with a smooth interface between the outer rectal wall and perirectal fat was classified as T1/T2. An indistinct or spiculated border between the outer rectal wall and the surrounding fat at the level of the tumor was considered as evidence of perirectal invasion (T3). Tumor infiltration into adjacent organs was considered stage T4. Lymph nodes were considered to be positive for metastasis if at least one perirectal lymph node with a short axis diameter of more than 3 mm was found. MRF was considered involved in all T4 tumors. In T3 tumors, MRF was considered involved when the distance between the tumor margin and the MRF was <1 mm. MRF was also considered involved when the distance between enlarged lymph node and MRF was <1 mm.

MDCT findings were then correlated with surgical and histopathological findings. Intra-operative staging was carried out using frozen section biopsy. It is important to mention here that all patients with T4 lesions on MDCT and in whom surgical procedure was carried out received adjuvant chemo-radiotherapy to prevent recurrence. Each specimen was opened along the opposite side of the tumor proximal to the segment containing the tumor. Before the specimens were fixed in formalin, a pathologist harvested the lymph nodes in the mesorectum. All specimens were fixed by total immersion in buffered formalin for 48 h and were sliced transversely at 3-mm intervals. The slices were embedded in paraffin, sectioned and examined histologically after H and E staining. The extent of local tumor staging in each slice was assessed according to the tumor component of the TNM system.

The sensitivity, specificity, positive predictive value, negative predictive value and accuracy rates were calculated.

 Results



Radiological findings

T1 and T2 rectal cancers were grouped together in our study. This is because this radiological modality is relatively new in our country and less expertise of our radiologists to differentiate between these two early lesions. However, there was no difficulty to differentiate T2 from T3 or T3 from T4 lesions. T3 was the most common tumor found followed by T1/T2 as is evident from [Table 1]. [Figure 1]a shows MDCT scan (axial view) of an 80-year-old female revealing eccentric thickening of the rectal wall causing partial lumen obliteration. Perirectal fat planes are maintained (T2 lesion). [Figure 1]b shows coronal MPR image of same MDCT. No significant perirectal lymph nodes are seen (N0). [Figure 1]c shows MDCT scan (axial view) of 65-year-old male revealing big rectal tumor infiltrating perirectal fat (T3 lesion) with insignificant lymphadenopathy. [Figure 1]d shows MDCT scan of patient revealing a solitary liver metastasis.{Figure 1}{Table 1}

Type of surgery performed

All patients underwent surgical intervention. Lower anterior resection with total mesorectal excision (TME) was the most common surgical procedure performed (55%). Abdomino-perineal resection (APR) was performed in 23%, open and close laparotomy for unresectable growth was performed in 8 (15%) patients. Patients with T4 lesions on MDCT and in whom surgery was performed received adjuvant chemoradiotherapy to decrease chances of recurrence. [Figure 2]a and b shows resected specimen (arrows indicating tumors).{Figure 2}

Histopathological findings

A total of 44 resected specimens were sent immediately for histopathological examination and for correlation with radiological findings. T3 was the most common (54.5%) tumor detected on histopathological examination HPE, as shown in [Table 2]. T4 was identified after taking a biopsy from adjacent viscera. Nodal metastasis was found in 14 (32%) of patients.{Table 2}

Comparison of MDCT T-staging with intra-operative and histopathological T-staging

As shown in [Table 3], nearly 71.4% patients with T1/T2 lesion on MDCT were identified correctly as having T1/T2 lesion both intraoperatively as well as on histopathology. Four patients had T3 lesion on histopathology. Thus, there was under staging for T3 lesion in 4 patients on MDCT. On histopathology, out of 25 patients with T3 lesion on MDCT, 20 (80%) patients were identified correctly as having T3 lesion while 5 patients had T1/T2 lesion. Thus, there was over staging in 5 patients on MDCT for T1/T2 lesion. All 13 patients identified as having T4 lesion on MDCT were found to have T4 lesion intraoperatively using frozen section biopsy from adjacent viscera. Eight such patients had open-close laparotomy only (for unresectable tumor) and no specimen was sent for histopathological examination. In five patients, APR was done with histopathology revealing T4 lesion. Accuracy of MDCT in differentiating T1/T2 from T3 lesion at HPE was 77% with a sensitivity of 71.4% and specificity of 80%. Positive and negative predictive values were 66.7% and 83.3% respectively. Accuracy of MDCT in differentiating T3 from T4 lesion at surgery was 86.5% with sensitivity and specificity of 79% and 100% respectively. Positive and negative predictive values were 100% and 72.2% respectively. Accuracy of MDCT in differentiating T3 from T4 lesion at HPE was 100%. Accuracy of MDCT for T4 lesion at HPE was 100%.{Table 3}

Comparison of MDCT N-staging with intraoperative and histopathological N-staging

On MDCT, 17 (32.7%) patients had nodal (perirectal) metastasis (N+), whereas 35 (67.3%) had no nodal metastasis (N − disease), as shown in [Table 4]. Among patients with nodal metastasis, 4 patients had unresectable growth and only 13 specimens were sent for histopathology. Out of 13 specimens, 10 (77%) were identified correctly as having nodal metastasis on histopathology. Among 35 patients with N − disease on MDCT, 4 patients had unresectable growth and only 31 specimens were sent for histopathology. Out of 31 patients, 27 patients (87%) were identified correctly as having N − disease on histopathology. Accuracy of MDCT in differentiating N + from N − disease at histopathology was 84.1% with sensitivity and specificity of 77% and 87% respectively. Positive and Negative predictive values were 71.4% and 90% respectively.{Table 4}

 Comparison of MRF status on MDCT with histopathological MRF status



On MDCT, MRF was visualized in all patients, which was depicted as an isodense (same density as that of muscle), thin structure, enveloping mesorectum and surrounding the perirectal fat. Twenty patients had MRF involvement on MDCT. Thirteen patients with MRF involvement on MDCT had T4 disease and 7 patients had T3 disease. Among the 13 patients, eight had open and close laparotomy only and only five specimens were sent for histopathology. All five were identified to have MRF involvement on histopathology. Out of seven patients with T3 disease and MRF involvement on MDCT, histopathology correctly diagnosed MRF involvement in five patients. Thus, histopathology correctly identified MRF involvement in ten of twelve specimens [Table 5]. There were two false positive cases. Accuracy of MDCT in differentiating MRF + from MRF − at histopathology was 91% with sensitivity and specificity of 83.3% and 94% respectively. Positive and negative predictive values were 83.3% and 94% respectively.{Table 5}

Comparison of M-staging on MDCT with intra-operative M-staging

Metastatic liver deposits were found in 3 out of 52 (5.8%) patients on MDCT [Figure 1]d which was conformed intra-operatively, making MDCT 100% sensitive for distant metastasis.

[Table 6] depicts the overall results of MDCT in staging of rectal cancer. {Table 6}

 Discussion



Colorectal cancer is the second most common form of cancer in developed countries and is responsible for significant morbidity and mortality rates. Prognosis of cancer is directly related to the depth of tumor invasion beyond the bowel wall, lymph node metastasis and the tumor involvement of the circumferential resection margin (CRM). The accurate pre-operative loco-regional staging of rectal cancer is important in choosing and planning therapy and to decrease local recurrence by selecting appropriate patients for pre-operative neoadjuvant chemoradiotherapy.

Conventional CT is not able to differentiate and distinguish different layers of the rectal wall and has lower overall accuracy than EUS and MRI. The recent technical developments however have revolutionized the capability of CT and as a result it's clinical applications. The introduction of MDCT allowed faster scanning, thinner slice, increased spatial resolution and better image quality of both axial and MPR images. These advantages may increase accuracy of MDCT in the local staging of rectal tumor by improving evaluation of the rectal wall, mesorectum and MRF. In one study, [9] T-staging using MDCT was found to have accuracy of 86%, whereas another study [10] found an accuracy of 83%. In contrast to MRI, CT is more available, less expensive and less time consuming and is widely used to search for distant metastasis. Despite major progress of image quality with the multi-detector row technique, it's poor soft-tissue contrast resolution compared to MRI remains. [11] Despite improvements in CT technology, individual wall layers of the rectum cannot be demonstrated by MDCT making it impossible to differentiate T1 from T2 tumors on MDCT. Although low risk T1 tumors may benefit from transanal endoscopic microsurgery, the clinical value is limited by the impossibility of performing a complete intraoperative staging of nodal sites. Differentiation of T2 tumor from T3 tumor is very important because T3 tumors benefit from chemoradiotherapy. The crucial criterion of T3 tumor is infiltration of perirectal fat. In our study, we correctly staged 20 of 25 (80%) patients with T3 tumor. There was under staging in 4 patients on MDCT for T3 lesion and over staging in 5 patients for T1/T2 lesion. In the differentiation of T3 and T4 tumors, the MDCT criterion was the obliteration of fat planes between tumor and adjacent organ. MPR images also have major implications for improving the delineation of the tumor as opposed to adjacent organs. We correctly staged 13 patients with T4 disease and no false positive and false negative results. Various studies report that the combination of axial and MPR images were more accurate in the staging of T4 tumors than axial images alone. [10],[12],[13]

Lymph node involvement is important for prognosis and treatment planning of rectal cancer. Recently published studies [10],[12],[13],[14] with MDCT, which evaluated both axial and MPR images reported an accuracy rate between 78% and 96%. These studies concluded that MPR images increased accuracy of MDCT in the Nstaging by allowing more accurate measurement of lymph node and better differentiation of lymph nodes from small perirectal vessels. Although the main CT criterion for nodal involvement is the size of the lymph node, there is no consensus on the size cut-off value to define pathologic lymph nodes. Filippone et al. [10] accepted all the detectable lymph nodes involved if there is more than one node (if one node present, size criterion was 1 cm) and reported 80% accuracy in the N-staging. Kulinna et al. [12] used a 3 mm cut-off value and reported that two reviewers had 96% and 80% accuracy rates. Sinha et al. [13] used a 5 mm cut-off value and reported an 84.8% overall accuracy rate in the N-staging.

We used a 3 mm cut-off value and had an overall accuracy rate of 84%, sensitivity 77%, specificity 87%, PPV 71.4% and NPV 90% in the N-staging. In our study, 3/13 (23%) patients with N − disease were over staged as N + disease, whereas 4/31 (13%) patients with N + disease was down staged as N − disease. This data suggest that MDCT had no difficulty in the detection of lymph nodes, but had difficulty in the discrimination of benign from malignant lymph nodes. The inability to assess the internal architecture of lymph nodes is a major disadvantage of CT and additional nodal characteristics such as border, shape and enhancement could help to optimize lymph node staging.

An important risk factor for tumor recurrence after surgery is its relationship to the MRF, which actually defines the surgical CRM in TME surgery. [5],[15] Vliegen et al. [16] evaluated the accuracy of MDCT for the prediction of MRF involvement using MRI as a reference standard and reported accuracy of 54% and 66% for two observers. Low accuracy rate in their study may be due to thick slice thickness (5 mm) and evaluation of only axial images. Sinha et al. [13] reported 96.5% accuracy rate in the prediction of MRF involvement by using both axial and MPR images. They concluded that MPR images increase accuracy rate of MDCT in the prediction of MRF involvement. In our study, the accuracy rate of MDCT in the prediction of CRM involvement was 91%, which is almost similar to study of Sinha et al. High accuracy rate of CRM involvement in our study was due to thin slice thickness, evaluation of high resolution MPR images and evaluation of MRF without distension of rectum. Distension of the rectum leads to a significant reduction in the CRM, [17] which may lead to false positive result of CRM involvement especially in T3 tumors associated with tumoral deposit close to CRM.

 Conclusion



From the above study evaluating the role of MDCT in pre-operative staging of rectal cancer, we conclude that MDCT is a reliable radiological tool for local staging of rectal cancer with excellent accuracy rates for T and N staging of rectal cancer.

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