Published online before print February 27, 2004, 10.1148/radiol.2311030036
(Radiology 2004;231:117-122.)
© RSNA, 2004
Depiction and Local Staging of Rectal Tumors: Comparison of Transrectal US before and after Water Instillation1
Sooah Kim, MD,
Hyo K. Lim, MD,
Soon Jin Lee, MD,
Dongil Choi, MD,
Won Jae Lee, MD,
Seong Hyun Kim, MD,
Min Ju Kim, MD and
Jae Hoon Lim, MD
1 From the Department of Radiology and Center for Imaging Science, Samsung Medical Center, Sungkyunkwan University School of Medicine, 50 Ilwon-Dong, Kangnam-Ku, Seoul 135–710, Korea. From the 2002 RSNA scientific assembly. Received January 9, 2003; revision requested March 20; final revision received August 7; accepted September 29. Address correspondence to H.K.L. (e-mail: hklim@smc.samsung.co.kr).
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ABSTRACT
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PURPOSE: To determine whether transrectal ultrasonography (US) with intrarectal water instillation can improve the depiction and accuracy of US in local staging of rectal tumors.
MATERIALS AND METHODS: Between October 1999 and February 2002, 63 patients (mean age, 56 years; age range, 23–91 years) with 63 rectal tumors were evaluated with transrectal US before and after intrarectal water instillation. Transrectal US examinations were performed with a 7–10-MHz radial transducer. Immediately after the first transrectal US examination, the rectal lumen was filled with 50–150 mL of degassed water, and a second US examination was performed. All patients underwent surgery within 1 month after transrectal US. Depiction of the tumor was compared between the two methods. The McNemar test was used to compare the accuracy between the two techniques in local staging of the tumor by using pathologic findings in the resected specimen as the standard.
RESULTS: The tumors ranged from 0.5 to 8.0 cm (mean, 2.8 cm) as measured at pathologic evaluation. All 63 tumors were clearly depicted at transrectal US after water instillation, while only 42 (67%) of the tumors were depicted at transrectal US before water instillation. In the 42 tumors clearly depicted at transrectal US examinations both before and after water instillation, the accuracy of transrectal US in local tumor staging was significantly higher after water instillation (85.7% [36 of 42]) than before water instillation (57.1% [24 of 42]; P < .001).
CONCLUSION: Water instillation during transrectal US examination of rectal tumors improves the depiction and local staging of the tumors.
© RSNA, 2004
Index terms: Neoplasms, staging, 757.32 • Rectum, neoplasms, 757.32 • Rectum, US, 757.12988 • Ultrasound (US), contrast media • Ultrasound (US), technology
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INTRODUCTION
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In the past few years, minimally invasive procedures have been increasingly used in the management of rectal tumors. Different treatment modalities, including endoscopic local excision or abdominoperineal resection, are available for rectal cancers depending on the location, size, and stage of the tumor. A sensitive technique for preoperative staging of rectal cancer could improve the selection of patients who can be effectively treated with minimally invasive procedures. Therefore, accurate preoperative staging is essential for determining optimal treatment.
Endoscopy and double-contrast barium enema examination can demonstrate the intraluminal component of the lesion, and the extent of the tumor in the bowel wall layers and the extraluminal component of the tumor can be evaluated with transrectal ultrasonography (US), computed tomography (CT), and magnetic resonance (MR) imaging. Although CT has been the most widely used method for staging of rectal carcinoma, it is not satisfactory in the evaluation of depth of tumor invasion because of its inherent resolution limitation. Transrectal US and endorectal coil MR imaging are known to be superior to CT in assessing local extension of tumor and lymph node involvement. According to published study results (1,2), the diagnostic accuracy of transrectal US was similar to that of endorectal coil MR imaging for determining depth of invasion of rectal carcinomas. Major advantages of transrectal US (as opposed to MR imaging) are convenience and shorter examination time.
In most studies in which transrectal US and endoscopic US were used for colorectal cancer staging, US examinations were performed by infusing degassed water into a latex balloon surrounding the transducer or by instilling water into the lumen of the rectum to produce a better acoustic window (2–7). However, to the best of our knowledge, no studies have been focused on comparison of transrectal US before and after water instillation. The purpose of our study was to determine whether transrectal US with intrarectal water instillation can improve depiction and accuracy in the local staging of rectal tumors.
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MATERIALS AND METHODS
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Patients
Between October 1999 and February 2002, a total of 121 patients were referred to our department for transrectal US examination of an anorectal mass. Of these patients, 27 patients who underwent transrectal US only after water instillation were excluded from the study. Another 19 patients were excluded because they did not undergo surgery at our institution. We also excluded 12 patients with a prior history of radiation therapy (n = 1), postoperative recurrent tumor (n = 1), anal cancer (n = 3), or benign inflammatory or granulomatous lesions (n = 7). The remaining 63 patients (mean age, 56 years; age range, 23–91 years) formed the study population; these patients underwent transrectal US examinations both before and after water instillation and also underwent surgical resection of the rectal tumors. There were 31 men (mean age, 58 years; age range, 29–91 years) and 32 women (mean age, 57 years; age range, 23–76 years). All patients were found to have rectal tumors at endoscopic examination, and biopsy procedures were performed in all tumors detected.
The location of a tumor was recorded according to the endoscopic finding, and endoscopic reports were reviewed by one radiologist (S.K.). All endoscopic examinations were performed before transrectal US. The interval between endoscopic and transrectal US examinations ranged between 1 day and 24 days (mean, 7.0 days). All patients underwent surgery within 1 month (mean, 7.4 days; range, 1–30 days) after transrectal US examinations. The surgical procedures included transanal endoscopic microsurgery in 43 patients, low anterior resection in 12 patients, and abdominoperineal resection in eight patients. Results at pathologic examination of resected specimens confirmed the diagnosis of the 63 tumors as follows: 48 adenocarcinomas, six villous adenomas, three tubular adenomas, two villotubular adenomas, two carcinoids, one mucinous carcinoma, and one fibroepithelial polyp. This study was approved by our institutional review board, and written informed consent was obtained from all patients.
Transrectal US Technique
All transrectal US examinations were performed with a 7–10-MHz rigid radial transducer (Brüel & Kjaer, Copenhagen, Denmark) by either one of two abdominal radiologists (S.K., S.J.L.; 4 and 7 years of experience performing transrectal US, respectively). They were provided with full knowledge of the results of endoscopic examinations. Patients were asked to perform rectal cleansing 2–3 hours prior to transrectal US examination with two rectal suppository pills (bisacodyl, Dulcolax suppository; Boeringer Ingelheim Korea, Chung Ju, Korea). The initial transrectal US examination was performed without water instillation. An anechoic hard plastic cone (18-mm diameter, 45-mm length), covering the distal portion of the probe, was filled with 3 mL of degassed water and wrapped in a rubber condom. While the patient was lying in the left lateral decubitus position, the transducer was inserted into the anus and advanced as deeply as possible into the rectum. As the transducer was slowly pulled back, serial images of the entire length of the rectum and anal canal were obtained. The transducer we used was equipped with a mechanical rotating probe that provided 360° anorectal images.
After the first transrectal US examination, we removed the transducer from the anus, and 50–150 mL of degassed water was instilled in the rectal lumen by using an enema syringe. The same transducer that we had used to perform transrectal US without water instillation was then inserted, and a second US examination was performed according to the same procedures. If the rectal lumen was inadequately distended with an initial water instillation of 50 mL, additional water was instilled until the lumen of the rectum was well distended without folding of the rectal wall. There was little or no water leakage, and the patients tolerated all procedures without any complaint. Total examination time for each transrectal US examination was recorded. The patients were asked to expel intrarectal water immediately after the second transrectal US examination. The total examination time for each patient was 7–44 minutes (mean, 14.8 minutes).
Image Analysis
All transrectal US images were archived with a picture archiving and communication system, or PACS (PathSpeed workstation; GE Medical Systems, Milwaukee, Wis). The two abdominal radiologists who had performed the transrectal US examinations retrospectively analyzed the images, controlling window level and center settings at the PACS workstation, and had no knowledge of the final outcome in each case. They reviewed all transrectal US images obtained in one patient at the same time. A standard questionnaire was completed regarding each case. All transrectal US images were reviewed twice, with a 1-week interval and a different order between the two sessions; this was done to decrease the interpretational biases. During the initial interpretation session, transrectal US images obtained before water instillation were reviewed first, and transrectal US images obtained with water instillation were reviewed second. The order of interpretation was reversed during the second session. A final decision was made by consensus in each case. The transrectal US images were evaluated for the grade of tumor depiction and for the accuracy of preoperative local staging of the depicted rectal tumors. Lymph node staging was not included in this study.
Depiction of the tumor was graded on the basis of the visualization of the tumor and a transitional zone between the tumor and the normal rectal wall, as follows: grade 0, no depiction of the tumor; grade 1, depiction of part of the tumor, but no depiction of a transitional zone; or grade 2, depiction of the entire tumor with a clearly visible transitional zone.
The depth of invasion by the tumor was evaluated according to the TNM classification system, which was adjusted for US as described by Hildebrand et al (8). The infiltration depth of the tumor at US (uT stage) was interpreted as follows: uT1 was diagnosed when the middle echogenic layer (representing submucosa) was irregularly thinned by a hypoechoic mass. Complete disruption of submucosa, often coupled with thickening of the outer hypoechoic layer (representing muscularis propria), was interpreted as uT2. When the border between the proper muscle layer and the outer echogenic layer (interpreted as serosa or perirectal fat) was irregular or serrated, a uT3 tumor was diagnosed. When the mass invaded an adjacent organ, a diagnosis of uT4 was made.
The information regarding the location and size of the tumors was obtained from the endoscopic reports by one radiologist (S.K.). The grade of tumor depiction was compared between transrectal US images acquired before and after water instillation. The preoperative local staging at transrectal US (uT staging) before and after water instillation was compared with the histopathologic findings from the resected specimen (pT staging); this comparison was performed for only the 42 patients with a visible transitional zone between the tumor and normal rectal wall (grade 2 depiction). We failed to stage 21 tumors that had either grade 0 or grade 1 depiction at transrectal US before water instillation, because the tumors were not depicted or the transitional zone was not identified. Therefore, full sets of data for uT-staging comparison were available for only 42 patients with grade 2 depiction (32 adenocarcinomas, five villous adenomas, two villotubular adenomas, two tubular adenomas, and one mucinous carcinoma). One radiologist (S.K.) reviewed all pathologic evaluation reports, with an emphasis on the size and depth of invasion of the tumors.
Statistical Analysis
Statistical analysis was performed with a statistical software package (SPSS for Windows, version 9.0; SPSS, Chicago, Ill). A power analysis was performed to determine whether the resultant sample size was of sufficient magnitude to support confidence in the outcome results within predetermined confidence limits. For comparison of the accuracy in local staging of the tumors, we used the McNemar test. A P value of less than .05 was considered to indicate a statistically significant difference.
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RESULTS
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The locations of the tumors at endoscopic examinations were 2.0–12.0 cm (mean, 7.0 cm) from the anal verge. The mean size of the tumors at pathologic examination of the resected specimen was 2.8 cm (range, 0.5–8.0 cm). Among a total of 63 tumors, 34 were classified as pT1, 18 were classified as pT2, and 11 were classified as pT3 at pathologic examination.
With respect to the grade of tumor depiction, 17 tumors were grade 0, four tumors were grade 1, and 42 tumors were grade 2 at transrectal US before water instillation, whereas all 63 tumors were grade 2 at transrectal US with water instillation (Fig 1). Transrectal US with water instillation increased the grade 2 depiction rate from 67% (42 of 63) to 100% (63 of 63). The size of the 21 tumors with either grade 0 or grade 1 depiction at transrectal US before water instillation ranged from 0.5 cm to 4.3 cm (mean, 2.2 cm).
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Figure 1a. Transverse transrectal US images of small pT1 adenocarcinoma in a 52-year-old man. (a) Scan obtained before water instillation does not depict the mass. (b) Scan obtained after instillation of 50 mL of degassed water clearly shows a small hypoechoic mass (arrows), 1.2 cm in diameter, in the rectal wall between 10- and 11-o’clock positions. The tumor is confined to the mucosal and submucosal layers (pT1).
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Figure 1b. Transverse transrectal US images of small pT1 adenocarcinoma in a 52-year-old man. (a) Scan obtained before water instillation does not depict the mass. (b) Scan obtained after instillation of 50 mL of degassed water clearly shows a small hypoechoic mass (arrows), 1.2 cm in diameter, in the rectal wall between 10- and 11-o’clock positions. The tumor is confined to the mucosal and submucosal layers (pT1).
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The results of local tumor staging with transrectal US and pathologic examination are summarized in Table 1. The 21 tumors with either grade 0 or 1 at initial transrectal US were excluded because full sets of data for uT-staging comparison were available for only the 42 tumors with grade 2 depiction. Overall accuracy of T staging was 57.1% at transrectal US before water instillation and 85.7% at transrectal US after water instillation (Table 2). The accuracy of T staging was significantly higher at transrectal US after water instillation than at transrectal US before water instillation (P < .001). At transrectal US before water instillation, the frequency of understaging was 14.3% (six of 42), whereas that of overstaging was 28.6% (12 of 42). At transrectal US after water instillation, the frequency of understaging and overstaging decreased to 9.5% (four of 42) and 4.8% (two of 42), respectively (Figs 2–4). The T-staging results of transrectal US before water instillation were concordant with those of transrectal US after water instillation in 71.4% (30 of 42). In uT3 tumors, no statistically significant difference was noted between two techniques (P = 1.0) (Fig 5). According to a power analysis, a sample of 21 patients was required with a significance level of 5% and power of 90%, to detect the observed accuracy difference of 0.286 between the two techniques, with the observed proportion of discordant pairs of 0.31. Therefore, 42 patients constitute a sufficient sample to support confidence in the outcome results.
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Figure 2a. Images show pT2 adenocarcinoma in the midrectum in a 62-year-old man. (a) Transverse transrectal US scan obtained before water instillation shows a hypoechoic mass (arrows) with irregular margins in the rectal wall between 4- and 9-o’clock positions, which extends through the muscularis propria (uT3). (b) Transverse transrectal US scan obtained after water instillation shows a hypoechoic mass (arrowheads) that invades the muscularis propria and was interpreted as uT2, but the perirectal fat is clear. (c) Histologic slide of the resected specimen shows adenocarcinoma (arrows) invading the muscularis propria without infiltration of the perirectal fat (F) (pT2). (Hematoxylin-eosin stain; original magnification, x1.)
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Figure 2b. Images show pT2 adenocarcinoma in the midrectum in a 62-year-old man. (a) Transverse transrectal US scan obtained before water instillation shows a hypoechoic mass (arrows) with irregular margins in the rectal wall between 4- and 9-o’clock positions, which extends through the muscularis propria (uT3). (b) Transverse transrectal US scan obtained after water instillation shows a hypoechoic mass (arrowheads) that invades the muscularis propria and was interpreted as uT2, but the perirectal fat is clear. (c) Histologic slide of the resected specimen shows adenocarcinoma (arrows) invading the muscularis propria without infiltration of the perirectal fat (F) (pT2). (Hematoxylin-eosin stain; original magnification, x1.)
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Figure 2c. Images show pT2 adenocarcinoma in the midrectum in a 62-year-old man. (a) Transverse transrectal US scan obtained before water instillation shows a hypoechoic mass (arrows) with irregular margins in the rectal wall between 4- and 9-o’clock positions, which extends through the muscularis propria (uT3). (b) Transverse transrectal US scan obtained after water instillation shows a hypoechoic mass (arrowheads) that invades the muscularis propria and was interpreted as uT2, but the perirectal fat is clear. (c) Histologic slide of the resected specimen shows adenocarcinoma (arrows) invading the muscularis propria without infiltration of the perirectal fat (F) (pT2). (Hematoxylin-eosin stain; original magnification, x1.)
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Figure 3a. Transverse transrectal US images of villotubular adenoma in a 63-year-old woman. (a) Scan obtained before water instillation shows a mass (arrows) between 6- and 12-o’clock positions that was interpreted as cancer invading the muscularis propria (uT2). (b) On a scan obtained after water instillation, each layer (SM = submucosa, MP = muscularis propria, F = perirectal fat) is clearly identified. The mass was interpreted as uT1. Villotubular adenoma (not shown) confined to the mucosal layer was confirmed after surgery.
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Figure 3b. Transverse transrectal US images of villotubular adenoma in a 63-year-old woman. (a) Scan obtained before water instillation shows a mass (arrows) between 6- and 12-o’clock positions that was interpreted as cancer invading the muscularis propria (uT2). (b) On a scan obtained after water instillation, each layer (SM = submucosa, MP = muscularis propria, F = perirectal fat) is clearly identified. The mass was interpreted as uT1. Villotubular adenoma (not shown) confined to the mucosal layer was confirmed after surgery.
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Figure 4a. Images show pT2 adenocarcinoma in the midrectum in a 53-year-old woman. (a) On a transverse transrectal US scan before water instillation, a polypoid hypoechoic mass (arrows) between 9- and 11-o’clock positions is noted. The outer hypoechoic muscle layer (MP) appears intact (uT1). (b) On a transverse transrectal US scan after water instillation, it was also interpreted as a uT1 lesion (arrowheads). (c) Microscopic slide of the resected specimen reveals that the tumor cells (*) extend to the muscularis propria (arrows) (pT2). (Hematoxylin-eosin stain; original magnification, x40.)
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Figure 4b. Images show pT2 adenocarcinoma in the midrectum in a 53-year-old woman. (a) On a transverse transrectal US scan before water instillation, a polypoid hypoechoic mass (arrows) between 9- and 11-o’clock positions is noted. The outer hypoechoic muscle layer (MP) appears intact (uT1). (b) On a transverse transrectal US scan after water instillation, it was also interpreted as a uT1 lesion (arrowheads). (c) Microscopic slide of the resected specimen reveals that the tumor cells (*) extend to the muscularis propria (arrows) (pT2). (Hematoxylin-eosin stain; original magnification, x40.)
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Figure 4c. Images show pT2 adenocarcinoma in the midrectum in a 53-year-old woman. (a) On a transverse transrectal US scan before water instillation, a polypoid hypoechoic mass (arrows) between 9- and 11-o’clock positions is noted. The outer hypoechoic muscle layer (MP) appears intact (uT1). (b) On a transverse transrectal US scan after water instillation, it was also interpreted as a uT1 lesion (arrowheads). (c) Microscopic slide of the resected specimen reveals that the tumor cells (*) extend to the muscularis propria (arrows) (pT2). (Hematoxylin-eosin stain; original magnification, x40.)
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Figure 5a. Images show pT3 adenocarcinoma in the midrectum in a 53-year-old woman. (a) Transverse transrectal US scan before water instillation shows that the hypoechoic tumor with irregular borders (arrows) between 11- and 3-o’clock positions penetrates the perirectal fat (F) (uT3). (b) Transverse transrectal US scan after water instillation shows the tumor (arrowheads), which had been interpreted as penetrating into the perirectal fat (F) and staged as uT3. (c) Microscopic slide of the resected specimen reveals that the tumor cells (arrows) infiltrate the perirectal fat (F) (pT3). (Hematoxylin-eosin stain; original magnification, x40.)
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Figure 5b. Images show pT3 adenocarcinoma in the midrectum in a 53-year-old woman. (a) Transverse transrectal US scan before water instillation shows that the hypoechoic tumor with irregular borders (arrows) between 11- and 3-o’clock positions penetrates the perirectal fat (F) (uT3). (b) Transverse transrectal US scan after water instillation shows the tumor (arrowheads), which had been interpreted as penetrating into the perirectal fat (F) and staged as uT3. (c) Microscopic slide of the resected specimen reveals that the tumor cells (arrows) infiltrate the perirectal fat (F) (pT3). (Hematoxylin-eosin stain; original magnification, x40.)
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Figure 5c. Images show pT3 adenocarcinoma in the midrectum in a 53-year-old woman. (a) Transverse transrectal US scan before water instillation shows that the hypoechoic tumor with irregular borders (arrows) between 11- and 3-o’clock positions penetrates the perirectal fat (F) (uT3). (b) Transverse transrectal US scan after water instillation shows the tumor (arrowheads), which had been interpreted as penetrating into the perirectal fat (F) and staged as uT3. (c) Microscopic slide of the resected specimen reveals that the tumor cells (arrows) infiltrate the perirectal fat (F) (pT3). (Hematoxylin-eosin stain; original magnification, x40.)
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DISCUSSION
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In general, local excision of early tumors of the distal and middle third of the rectum is generally performed by using the transanal technique. The ideal candidate for transanal local excision is a patient with a rectal tumor that is less than 4 cm in diameter, located less than 10 cm from the anal verge, well or moderately differentiated, and preoperatively staged as T1 or T2 (2,9). At our institution, patients with T1 rectal carcinomas that are not poorly differentiated at histologic evaluation, are less than 3 cm in diameter, and involve less than one-fourth the circumference of the rectal lumen are candidates for transanal endoscopic microsurgery. In the selected patients with T2 rectal carcinomas, transanal endoscopic microsurgery is also performed in combination with postoperative chemoradiation therapy. To select the optimal treatment methods, therefore, accurate preoperative staging of the rectal cancer is important and will benefit patients in terms of quality of life.
Transrectal US can directly demonstrate whole layers of the rectal wall and thus make it possible to assess the depth of tumor infiltration. For accurate preoperative staging, however, the entire tumor should be well depicted at transrectal US. When the tumor is too small or the rectum is collapsed and compressed by a rigid transducer, it is difficult to detect and assess the tumor completely. In contrast, when the tumor is too big, attenuation of the ultrasound beam and shadowing from the bulky mass can occur, which prevent adequate visualization of the tumor base. Adherent feces can also produce shadowing artifacts. Plication and Houston valves of the rectal wall can produce image blurring (10). Therefore, for complete evaluation of a tumor, and to provide an optimal sonic window for rectal US, an adequate sonographic medium should be applied. This can be achieved by attaching a water-filled balloon to the tip of the transducer at endoscopic US or by filling the rectal lumen directly with water. With the first technique, the pressure effect of the balloon on the rectal wall may make it difficult to identify individual layers. In addition, because of size limitation of the balloon, part of the balloon at the tip of the endoscope may not make close contact with the rectal wall. Unless the expanding balloon directly contacts the bowel wall, ballooning results in only an increase of the artifactual anechoic area (10). We believe that the anatomy of the rectal wall can be depicted more easily with direct instillation of water into the rectum than with a water-filled balloon.
The accuracies of transrectal US in local staging of rectal tumors and of regional lymph node involvement have been reported to be 81%–91% and 58%–83%, respectively (11–13). In our study, the accuracy (57.1%) for local tumor staging with transrectal US before water instillation was inferior to those reported in other studies. This discrepancy in the results may be explained by the different populations of patients included in the studies and by the different techniques used. In the previous studies, endoscopic US with a water-filled balloon was used, while in our study we used a rigid transducer coupled with a water-filled balloon. Before we used transrectal US with intrarectal water instillation, we had performed all transrectal US examinations without water instillation for years. The results of transrectal US without water instillation were not satisfactory in comparison with our expectations. That is the main reason why we developed a transrectal US technique using intrarectal water instillation. By analyzing the accuracy of T staging separately for each lesion group, we found that transrectal US after water instillation showed an accuracy of 100% for T1 lesions, while accuracies for T2 and T3 lesions were 66.7% and 80.0%, repectively. These results suggest that transrectal US after water instillation is particularly valuable in discriminating T1 lesions from more advanced cancer.
A major problem in local staging of rectal cancer is overstaging and, to a lesser degree, understaging is also a concern (7,14). There are some histopathologic explanations for overstaging. Desmoplastic or inflammatory reaction surrounding a tumor may be responsible for overstaging because it cannot be differentiated from tumor infiltration (7,14,15). In preoperative biopsy, necrotic and hemorrhagic microfoci in the tumor and rectal wall can also produce overstaging (15). Overstaging has been reported with transrectal US in 4.5%–34.5% and understaging has been reported in 2.0%–5.5% of cases (14). In our study, overstaging at transrectal US before water instillation (28.6%) was much higher than that at transrectal US after water instillation (4.8%). We believe that the use of water instillation is a reliable method to reduce overstaging of rectal tumors because it decreases artifacts resulting from the tumor itself and from feces, and it increases echogenicity. In addition, if the rectal lumen is adequately distended, individual wall layers can be better delineated and plication of the rectal wall can be prevented. If the scanning plane is not perpendicular to the bowel axis, image blurring may occur. Therefore, an attempt should be made to keep the transducer in the middle of the lumen during the scanning.
The limitations of this study include the small population, the especially small number of T2 and T3 lesions, and the fact that we did not attempt to evaluate lymph node staging. To address these issues, further studies with a large population of patients are needed, particularly with patients who have received preoperative chemoradiation therapy, in whom downstaging is expected. Another limitation is the biases in image interpretation caused by the fact that this is a retrospective study. We tried to decrease such biases by interpreting the images twice, in an alternate fashion and with a 1-week interval. To avoid this limitation, a further prospective study with randomization is needed.
In spite of these limitations, our results indicate that transrectal US after water instillation can improve the depiction and accuracy in local staging of rectal tumors. Therefore, we recommend intrarectal water instillation for the local staging of rectal tumors at transrectal US examinations.
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ACKNOWLEDGMENTS
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The authors thank Seon Woo Kim, PhD, of Samsung Biomedical Research Institute, Seoul, Korea, for her assistance with the statistical analysis.
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FOOTNOTES
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Author contributions: Guarantors of integrity of entire study, H.K.L., S.K.; study concepts, H.K.L.; study design, H.K.L., S.J.L., S.K.; literature research, S.K., M.J.K., S.H.K., D.C.; clinical studies, S.K., S.J.L.; data acquisition, S.K., S.J.L., D.C.; data analysis/interpretation, S.K., S.J.L.; statistical analysis, S.H.K., D.C.; manuscript preparation, S.K., S.J.L.; manuscript definition of intellectual content, H.K.L.; manuscript editing, H.K.L., W.J.L., J.H.L.; manuscript revision/review and final version approval, all authors
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ABSTRACT
INTRODUCTION
