ABSTRACT
Virtual colonoscony is a potentially powerful tool for noninvasive colorectal evaluation. In the past 20 years, the radiology of colorectal cancer has evolved from the barium enema to advanced imaging modalities like magnetic resonance imaging [MRI], virtual colonoscopy and positron emission tomography [PET]. Virtual colonoscopy is rapidly evolving and might considerably change the imaging of colorectal cancer in the near future. The use of virtual colonoscopy for screening purposes and imaging of the colon in occlusive cancer or incomplete colonoscopies is currently under evaluation [Pijl et al., 2002]. CT colonography has been proposed as an alternative procedure for the examination of colorectal cancer patients because it is not limited to endo-luminal exploration of the colon [Royster et al., 1997], it reaches the cecum, even in cases of obstructive lesions; and combines study of the colon with evaluation of target organs for metastases, in particular the liver [Neri et al, 2002, Horton et al., 2000, Morrin et al., 2000, Fenlon et al., 1999, Macari et al., 1999, and Morrin et al., 1999]. The aim of our study was to evaluate CT colonography in patients with a clinical suspicion of colorectal cancer in comparison with colonoscopy and histopathological findings after surgery. This study included a total of 15 patients [9 men, 6 women; mean age, 53 years; age range [35-67 years] with clinical suspicion of colorectal cancer. The study was conducted from September 2000 through May 2004 in Al Jedani Group of Hospitals and Riyadh Care Hospitals in Saudi Arabia. For all patients the followings were done. o History taking and clinical examination. o Routine investigations. o Colonoscopy with biopsy if possible. o CT colonography. o Operative resection of the tumor when indicated. o Histopathological examination of the operative specimen: CT Colonographic Technique: Before CT scanning, room air was insufflated through a rectal enema tube from a bag containing room air and had a 2,000-mL maximum capacity. The abdominal CT study was performed before and after intravenous injection of iodinated contrast agent, iodixanol [Visipaque 320; Nycomed Amersham, Oslo, Norway]; 140 mL of contrast agent was administered at 3 mL/sec. CT colonographic analysis was performed by a radiologist. Evaluation included that of the endoluminal and extracolonic compartments. Colonic evaluation included that for the presence of wall thickening, cancers, polyps, and wall discontinuity. The liver was evaluated in an attempt to detect metastases. Acquired CT data were transferred to a computer system which permits obtaining multiplanar three-dimensional reformations of the air-distended colon, as well as an endoluminal perspective through the distended colonic lumen. Our 15 patients included 12 cases of colorectal cancer and 3 non malignant cases [one normal case, one case of ulcerative colitis and one case of diverticular disease]. The conventional colonoscopy diagnosed all the 12 cases of colorectal cancer. It was completed in only 7 patients [58.3%]. It could not be completed in 5 patients [41.7%]; 3 cases [25%] with distal occlusive carcinoma with inability to proceed proximally and 2 cases [16.7%] with patient's in tolerance to complete the colonoscopy. A distal occlusion [located in the rectum, sigmoid colon, or descending colon] was found, and colonoscopy failed to enable exploration of the colon segments proximal to the site of occlusion. In the other 2 patients, colonoscopy enabled exploration of the colon lumen up to the sigmoid [one case] and splenic flexure [one case]. Furthermore, 3 of these 5 cases had synchronous cancer missed due to incomplete colonoscopy. Also, colonoscopy showed 2 false positive cases [13.3%] for cancer which proved to be normal by histopathology. CT colonography diagnosed all the 12 cases of colorectal carcinoma. It could visualize the entire colon in 115 of the 120 colonic segments [95.8%]. It had one false positive case and ruled out malignant lesion in 2 cases [13.3%] supposed to be malignant by colonoscopy. Also, it diagnosed 3 cases [25%] of synchronous cancer missed by colonoscopy and 3 cases [25%] of concomitant liver metastasis. All the 12 cases proved to be malignant were subjected to operative management with histopathological examination which confirmed malignancy. The operative findings revealed synchronous lesions in 3 cases [25%] which were diagnosed by CT colonography and not by colonoscopy. CT colonography revealed the presence of three hepatic lesions [diameter range, 2-5 cm] suspicious for metastases. These 3 cases of liver metastasis were confirmed intraoperatively. One liver hemangioma [diameter 2 cm] was detected with CT. CT colonography has good patient compliance and is a useful diagnostic modality in detecting colorectal neoplasms. Its main advantage is its ability to detect extracolonic pathology. CT colonography can be considered an important diagnostic technique to evaluate preoperatively the proximal colon in patients with distal occlusive carcinomas, as it gives better results than conventional colonoscopy, as well as being well tolerated and less invasive. Its' advantages over conventional colonoscopy included the ability to detect abnormalities proximal to obstructing carcinomas, accurate localization of abnormalities within the colon, and good patient tolerance. It may play an important role in future diagnosis of colorectal cancer and for screening patients at risk