in patients with obstructive colorectal cancer , where conventional colonoscopy can not traverse obstruction , clearance of the proximal colon remains a problem .
a 58-year - old woman presented to her physician with rectal bleeding and intermittent diarrhea . conventional colonoscopy revealed a bulky tumor which was diagnosed as rectal cancer .
slim optical colonoscopy ( pcf - p240al / i , olympus , tokyo , japan ) showed obstructive cancer in the rectosigmoid junction ( fig . 1 , arrow a ) and no information of the proximal side of the obstruction .
the patient then underwent multidetector - row computed tomographic ( ct ) colonography ( virtual colonoscopy ) for further evaluation of the proximal colon .
three - dimensional endoluminal  fly - through images revealed another protruded lesion ( fig .
diagnosis of synchronous double cancer was made by ct air - contrast enema image ( fig .
this ct data was not only used to create three - dimensional images but also to decide on a preoperative clinical staging .
laparoscopy - assisted high anterior resection was performed and t3 rectal cancer and t1 sigmoid colon cancer were confirmed in the resected specimen ( fig .
between 4.6 and 11% of patients with colorectal cancer have a second synchronous cancer [ 1 , 2 , 3 ] .
preoperative evaluation of the whole colon and rectum in patients with colorectal cancer is widely recommended .
optical colonoscopy is the current gold standard method as it examines the whole colon and rectum .
however , preoperative examination by optical colonoscopy may be hampered by occlusive colorectal cancer , and failure to find the presence of a synchronous cancer will change the surgical approach from circumscribed resection to resection of the involved segments .
ct colonography might be offered in preference to barium enema for incomplete colonoscopy [ 5 , 6 ] .
ct colonography has recently become a popular preoperative examination tool with significant improvement in quality of image due to a rapid progress in computer technology [ 7 , 8 ] .
ct colonography correctly showed synchronous double cancer in our case and provided crucial information for planning surgery .
we recommend that ct colonography should be used for evaluating the proximal side of obstructive colorectal cancer , as it is well tolerated and less invasive [ 6 , 9 ] .
 a 58-year - old woman presented to her physician with rectal bleeding and intermittent diarrhea . optical colonoscopy revealed a bulky tumor which was diagnosed as rectal cancer . 
 she was referred to our institution for further evaluation and treatment . 
 slim optical colonoscopy showed an obstructive cancer in the rectosigmoid junction and no information of the proximal side of the obstruction . 
 the patient then underwent computed tomographic ( ct ) colonography for further evaluation of the proximal side . 
 three - dimensional endoluminal  fly - through images revealed another protruded lesion in the proximal side of the obstruction . 
 diagnosis of synchronous double cancer was made by ct colonography . 
 this ct data was not only used to create three - dimensional images but also to decide on a preoperative clinical staging . 
 laparoscopy - assisted high anterior resection was performed and t3 rectal cancer and t1 sigmoid colon cancer were confirmed in the resected specimen . 
 follow - up optical colonoscopy revealed no other tumors . 
 ct colonography has recently become a popular preoperative examination tool with significant improvement in quality of image due to a rapid progress in computer technology . 
 ct colonography correctly showed synchronous double cancer in our case and provided crucial information for planning surgery . 
 we recommend that ct colonography should be used for evaluating the proximal side of obstructive colorectal cancer . 
Introduction
Case Report
Discussion