Colorectal Cancer 15

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J. H. Lim, MD

Professor of Radiology, 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

Colorectal Cancer 15

Jae Hoon Lim

15.1

Introduction

Double-contrast barium enema, colonoscopy, and computed tomography (CT) colonography are the procedures of choice for the detection and diagnosis of colorectal cancer; however, abdominal sonography may be the ﬁ rst test that patients with colon cancer undergo because they may present with nonspeciﬁ c gastrointestinal symptoms and signs (Schwerk et al.

1979). Careful sonographic examination of the colon and rectum may disclose a focal mass or mural thickening, and this may lead a physician to investigate for the diagnosis of colorectal cancer.

Increasing use of sonography in the initial evaluation of patients with abdominal disease may allow detection of unexpected tumors within the abdominal cavity (Schwerk et al. 1979; Price and Metreweli 1988; Rutgeerts et al. 1991). Absence of luminal

content in abnormal areas of the colon enabled us to detect a mass or mural thickening by sonographic examination. Sonographic detectability of colorectal cancer, intentionally or unexpectedly, warrants the inclusion of the bowel loops in the abdominal sonographic examination when a patient complains of symptoms suggesting colorectal cancer. In cases with incidentally detected masses or wall thickening of the colon or rectum, an appropriate diagnosis should be made by performing a barium enema, colonoscopy, or CT colonography.

15.2 Pathology

Colorectal cancer creates mass or segmental thickening of the wall (Fig. 15.1). Short segmental thickening is much more common than mass formation. Mass

C O N T E N T S

15.1 Introduction 129 15.2 Pathology 129

15.3 Transabdominal Sonographic Technique 130 15.4 Transabdominal Sonographic Findings of Colon Cancer 130

15.5 Transrectal Sonography 131 References 134

Fig. 15.1a,b. Two types of colorectal cancer. a Mass-form- ing colorectal cancer. b Short segmental wall thickening a b

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Transabdominal Sonographic Technique

Sonography is performed with 3.5- or 5.0-MHz sector or linear transducers. Sonography of the abdomen and pelvis is performed by moving the transducer slowly over the abdomen with gentle compression to displace adjacent bowel loops. Scanning through the course of the colon proceeds along the length of both ﬂ anks of the ascending and descending colon, across the midline of the upper part of the abdomen for the transverse colon, along the left side of the lower part of the abdomen from the descending colon toward the pelvic cavity for the sigmoid colon, and across the midline of the pelvic cavity for the rectum. The colon is differentiated from small bowel loops by the location and course of the bowel loops (Lim et al. 1994a,b).

15.4

Transabdominal Sonographic Findings of Colon Cancer

The normal thickness during the contraction stage is 2–3 mm, and wall thickness >5 mm is considered abnormal. Sonographic appearances of colorectal cancer reﬂ ect the pathology, i.e., either a bulky mass or segmental thickening of the colonic wall (Lim 1996). A mass may be small or relatively large, and is usually irregular or lobulated in contour (Fig. 15.2).

A large mass can be easily detected using sonography. The cluster of high-amplitude echoes denoting intraluminal gas and fecal content may be visible, centrally or eccentrically located in the mass (Price and Metreweli 1988).

The other common sonographic appearance of colorectal cancer is segmental (Fig. 15.3), eccentric,

Fig. 15.2a,b. Mass-forming colon cancer. a Transverse sono- gram of the right mid-abdomen shows a well-deﬁ ned, irregular, large mass, representing adenocarcinoma of the ascending colon. Note high-amplitude echoes denoting gas and fecal content in the lumen (l). b The CT image shows a large mass with air-containing lumen (l)

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should be performed for the detection of metastasis when a cancer is detected (Fig. 15.4). Inﬂ ammatory disease may present with a typical target appearance, but mural thickening in inﬂ ammatory disease is usually thinner and more uniform in thickness and involves a longer segment (Lim et al. 1994b).

Colon cancer may be detected during the work-up of anemia (Fig. 15.6), nonspeciﬁ c abdominal symptoms, or in patients with liver metastasis (Fig. 15.4).

15.5

Transrectal Sonography

For treatment of rectal cancer, minimally invasive surgery, such as transanal excision, transanal endoscopic microsurgery, total mesorectal excision, or abdominoperineal resection, are available depending on the location, size, and stage of the tumor ( Pricolo

Fig. 15.3a,b. Colon cancer with segmental wall thickening. a Sonogram of the left lower abdomen shows circumferential thickening of the co- lon wall, showing target sign (arrow). b Reformatted CT image of ab- domen with a short segmental, symmetrical thickening (arrow) of the wall of the sigmoid colon

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Fig. 15.4a,b. Rectal cancer with circumferential thickening of the wall. a Transverse sonogram of the pelvis shows circumferential thickening of the rectal wall. Note adjacent small metastatic lymph nodes (arrows). b Sagittal sonogram of the liver shows a well-deﬁ ned hepatic mass representing metastasis (arrow)

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and Potenti 2001; Zagoria et al. 1997). A sensitive technique for preoperative staging helps in deciding the type of surgery that can be effectively imple- mented with minimally invasive procedure; there- fore, accurate preoperative staging is essential for determining optimal treatment.

Endoscopy and double-contrast enema can dem- onstrate the intraluminal component of rectal cancer.

The extent of the tumor in the bowel layers and the extraluminal component of the tumor can be evalu- ated with transrectal sonography, CT, and magnetic resonance imaging (MRI). Although CT has been the most widely used method for staging, it has limita- tions in the evaluation of depth of tumor invasion because of inherent resolution limitation. Transrectal sonography and endorectal coil MRI are known to be superior to CT in assessing tumor depth through the wall, local extension of tumor, and lymph node involvement. The diagnostic accuracy of transrectal sonography was reported to be similar to endorectal coil MRI for determining depth of invasion of rectal carcinoma (Zagoria et al. 1997; Gualdi et al. 2000).

The major advantages of transrectal sonography, as opposed to MRI, are convenience and shorter examination time.

Transrectal sonographic examination for rectal cancer is performed with a 7- to 10-MHz rigid radial transducer. Patients are asked to perform rectal cleansing 2–3 h prior to the examination with rectal repository pills. Sonographic examination is performed with the patient in the left lateral decubitus position. Before introduction of transducer, 50–

150 ml of degassed water is instilled into the rectal lumen by using an enema syringe to improve depic- tion of the tumor and local staging. As the transducer is slowly pulled back, serial images of the entire length of rectum and anal canal are obtained.

Fig. 15.5a,b. Colon cancer with obstruction. a Transverse sonogram of the left mid-abdomen shows thickening of the wall of the descending colon (arrows) in patient with partial obstruction of the colon. b The CT image shows symmetric thickening of the wall of the descending colon (arrow) and dilated small bowel loops

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Fig. 15.6. Colon cancer detected during the work-up of iron-deﬁ ciency anemia. Oblique sagittal sonogram of the right upper abdomen shows a large mass in the hepatic ﬂ exure of colon, presenting as a “pseudokid- ney sign.” Note right kidney posterior to the lesion

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Fig. 15.7. Normal rectal wall. Transrectal sonographic appearances of the normal rectal wall and schematic drawing of histological anatomy and sonographic appearances of the rectal wall. 1 hyper- echoic: lumen/mucosal interface and superﬁ cial mucosa; 2 hypoechoic: deep mucosa including muscularis mucosa;

3 hyperechoic: submucosa plus sub- mucosa/muscularis propria interface;

4 hypoechoic: muscularis propria mi- nus interface with submucosa; 5 hyper- echoic: muscularis propria/perirectal interface and perirectal fat

Fig. 15.8. a Rectal cancer conﬁ ned to the mucosa (T1 cancer).

Transrectal sonogram shows a hypoechoic mass (arrows) with thinning of the submucosal layer. b Rectal cancer ex- tended to the submucosa (T2 cancer). Transrectal sonogram shows an irregular hypoechoic mass with interruption of the submucosal layer and thickening of the hypoechoic musclola- ris propria layer (arrows). c Rectal cancer involving the en- tire wall and perirectal fat (T3 cancer). Transrectal sonogram shows an irregular hypoechoic mass with interruption of the submucosa and muscle layers and serrated hypoechoic lesion in the hyperechoic perirectal fat space (arrows)

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imaging of tumor located 8–10 cm or above the anal verge when rigid probe is used, in the imaging of stenosing tumor, in depicting lymph nodes that are outside the range of transducer, and the technique is operator dependent.

References

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Pricolo VE, Potenti FM (2001) Modern management of rectal cancer. Dig Surg 18:1−20

Rutgeerts LJ, Verbanck JJ, Crape AW et al (1991) Detection of colorectal cancer by routine ultrasound. J Belge Radiol 74:11−13

Schaffzin DM, Wong WD (2004) Endorectal ultrasound in the preoperative evaluation of rectal cancer. Clin Colorectal Cancer 4:124−132

Schwerk W, Braun B, Dombrowski H (1979) Real-time ultrasound examination in the diagnosis of gastrointestinal tumors. J Clin Ultrasound 7:425−431

Zagoria RJ, Schlarb CA, Ott DJ et al (1997) Assessment of rectal tumor inﬁ ltration utilizing endorectal MR imaging and comparison with endoscopic rectal sonography. J Surg Oncol 64:312−317