Abdominal & Pelvic CT sensitivity

[Bob-Muler]

  Dear Doctor;
  Male, 40 year old.  Can you satisfy my curiosity?
  How sensitive would an abdominal/pelvic CT with oral contrast be in
  in visualizing a napkin ring growth in the distal sigmoid colon?
  (Axial images, 8mm intervals).
  Realizing CEA is not typically used as a screening blood test
  would it be unreasonable to perform a CEA in the following situation?
  Random red blood on ribbon thin stools. Random morning vomiting now.
  Continuous LLQ & RUQ pressure and pain.
  Elevated venous ammonia,increased from 108 to 122 uMoL/L.
  Increasing ESR from 8 to 15 to 23mm/HR.
  CBC normal, Monocytes High, .8 cumm.
  Random increases in other liver function test. GGT and Bilirubin.
  Alk. Phos. normal.
  Thanks.
  Robert Muller
____________________________________
Dear Bob Muller,
You have posed very interesting questions regarding the diagnosis of colon cancer.  When CT scans are performed in patients with colon cancer, there are some who will have a thickening of the colon wall and evidence of stranding into the fat.  These findings, however, are not specific to colon cancer.  Conditions such as diverticulosis and Crohn’s Disease can produce the identical radiologic finding.  In addition, there are some patients with documented colon cancer who have CT scans interpreted as normal.  I could not find numbers for the sensitivity and specificity of CT scans to diagnose colon cancer, but it is correct to say that the low predictive value of CT scanning excludes this test from being used to diagnose these cancers.
The important questions that the physician would ask your hypothetical patient are 1) Are thin stools a new finding or have your stools always been that way? 2) How frequently do you have a bowel movement and has the pattern changed? 3)Is the blood on the surface of the stool or is the blood mixed with the stool? (Blood on the surface iof the stool is usually indicative of a low rectal or anal source of bleeding.  The workup for this patient would be a sigmoidoscopy.  Blood mixed with the stool usually means that the bleeding site is above the rectum,  These patients need a colonoscopy to look for sources of bleeding.)  
Based on the history that you present (bleeding, change in stool caliber, abdominal pain) a colonscopy would be indicated. A CEA test is not sufficiently sensitive to detect cancer confined to the colon.  The symptom of vomiting and the abnormal liver tests are probably not explained on the basis of the colonic problem and other etiologies must be sought.
This response is offered for your general information and should not replace the conclusions drawn from a careful and complete evaluation by your physician.
If you wish to be seen at our institution, Henry Ford Hospital, please call our PHYSICIAN REFERRAL LINE at(313) 876-2393 and request consultation with Dr Fogel,

HFHSM.D.-rf
*keywords; colon cancer, CT scans
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