On MRIs, Small Bowel Follow-Throughs and CT Scans

Dr. W is apparently my surrogate GI until Dr. S is back in town.  He is concerned about my symptoms (the Weekly Throughput and ossified left intestine), suspects an obstruction (stricture, fibrosis, or scarring) and wants to do a small bowel follow through.

At this point, I realize that without these magnificent instruments of medical speculation, I really have no freaking idea whether the left side distension/rigidity is my sigmoid colon or duodenojejunal flexure (the former being almost directly anterior to the latter).  I also have no freaking idea what's going on in my Prednisone-resistant mid-lower small intestine.  What I do know from historical diagnosis is that I have ileal obstruction (on the right side) which has been fairly reticent during this flare; not particularly helpful in addressing the small bowel pain and left side distension/rigidity.

In the last two months, I've been recommended an MRI, a CT scan, and now a small bowel follow through (SBFT).  The first two were suggested by Dr. S, the last by his surrogate.  The reason endo/colonoscopies are not on this list is because they have shown zero new information about my new symptoms as they have developed over the last eleven years.  Endo/colonoscopies don't span a great breadth of the intestinal tract (endo goes down to the duodenum, colono goes up to the top left juncture of the descending colon).

For those who are equally confused as to why their GIs can't make up their minds about which procedure is best for diagnosing which kinds of Crohn's or IBD symptoms, below is a compilation of my findings.  The general concensus seems to be that SBFT are more accurate in identifying strictures, and MRI and CT are better at identifying fistulas, abscesses and active inflammation in deep tissue.

In a study comparing MRI and SBFT (Bernstein et al 2005):

"SBFT revealed additional information in four [patients], including a stricture (none found on MRI, n=1), jejunal site of obstruction versus unclear site on MRI (n-1), and ileosigmoid fistulas (n=2)."

"For tight strictures, SBFT gave information on number but did not delineate findings between the strictures, or on extramural disease.  Obstruction and stricture detection was comparable but characterization was more detailed with MRI."

In a study comparing MRI, CT and SBFT imaging of the small bowel (Lee et al 2009):

"The mean number of bowel segments other than the terminal ileum with active inflammation per patient was slightly higher as detected by using CT enterography and MR enterography than it was as detected by using SBFT.  However, these differences were not significant.  The level of agreement between the readers was excellent for CT enterography, MR enterography and SBFT."

"The low level of agreement observed for SBFT may reflect inherent disadvantages of this technique, including incomplete evaluation of bowel segments located deep in the pelvic cavity owing to overlapped bowel loops and suboptimal evaluation of the small bowel distal to the tight stricture (10, 12, 32)." (Note: The paper doesn't specify how the SBFT were conducted, but I know that during this procedure they have the option of pushing your guts to one side or another to get a better image if they want to, so in my opinion this observation is inaccuate)

"CT and MR enterography were more capable than was SBFT of depicting extraenteric complications of CD, including fistulas, sinus tracts, and abscesses.  Although our findings are consistent with findings in most previous studies (4, 10, 12, 33), conflicting results have been reported for the detection of enteric fistulas and sinus tracts (4, 10, 33).  Bernstein et al (10) compared MR enterography and SBFT in 30 patients with CD and found that SBFT allowed identification of two ileocolic fistulas that were missed using MR enterographic images."

In a study looking at the accuracy of CT enterography preoperative diagnosis in the small bowel (Vogel et al 2007):

"For the 36 patients, the presence or absence of stricture or fistula was correctly identified by CTE in 36 (100 percent) and 34 (96 percent), respectively." (Note: Since "preoperative diagnosis" can be assumed to refer to the presence of a stricture, I think it is implied, here, that the CT scan is an accurate way to identify small bowel obstruction.)

"SBFT is accurate in the prediciton of fistula, stricture and mucosal abnormalities with specificity and sensitivity reported in the 85 to 95 percent range (MacKalski & Bernstein 2006)."

"In the 18 patients with one or more strictures, CTE was correct for stricture number in 12 (67 percent)."

A review of Crohn's disease imaging advancements (Grand 2009):

"The small bowel series and barium enema are essentially historic examinations for the detection and evaluation of inflammatory bowel disease.  These studies, while effective at detecting mucosal abnormalities, are poorly tolerated by sick patients, provide assessment only of the bowel lumen (particularly the mucosa) and are physician dependent, limiting their reproducibility.  A properly performed and interpreted SBFT or BE is unfortunately a lost art..." (Note: Again, SBFT seems accurate for identifying fibrosis, but not deep tissue inflammation in active Crohn's)

"The ability to assess disease activity is probably the most important advantage of MRe over CTe.  Clinically, it is often difficult to distinguish between active and chronic changes of inflammatory bowel disease in symptomatic patients.  This distinction has become increasingly important with the advent of new, boilogic therapies for active inflammatory disease which, while extremely effective, are expensive and may also be potentially toxic.  Although beneficial for patients with active inflammatory disease, these agents do not benefit patients whose symptoms are secondary to a fibrotic stricture.  Rather, these latter patients will require surgery for symptomatic relief" (Note: Since I am currently on biologic therapy, it's pretty important that I be able to figure out whether the last three Remicade infusions were not even necessary.  If I end up needing surgery for a stricture as Dr. W suspects... I'm going to be pissed that Dr. S put me on the PPR combo so hastily.)

"Because negative contrast is used for CTe, small abscesses may be difficult to distinguish from loops of bowel and regular CT or MRe should be employed if abscess is suspected or in the immediate post-operative state." (Note: In agreement with Lee et al paper)