| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Clinical Observations |
1 Both authors: Department of Radiology, The University of Chicago, 5841 S Maryland Ave., Chicago, IL 60637.
Received December 15, 2004;
accepted after revision February 24, 2005.
Address correspondence to A. H. Dachman.
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CONCLUSION. Rotation of the cecum is geometrically complex and occurs in several planes. It explains previous anecdotal reports of false-negative diagnoses. When solid feces is suspected in the cecum based on mobility, the reviewer should take the time to carefully analyze mobility of the cecum using multiplanar images.
Keywords: colonography • colonoscopy • CT • gastrointestinal radiology
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
A secondary sign of feces may be its shape if it has angulated margins [7]. Laks et al. [8] found a surprisingly high 27% of polyps that appeared to move from a ventral to a dorsal location relative to the colonic surface when the patient was turned. Other investigators have given personal anecdotal communication of cases of mobility, particularly of the cecum, transverse colon, and sigmoid colon, causing the observer to misinterpret a lesion as mobile. We sought to study mobility of the cecum as seen on CT colonography to determine how often this potential pitfall exists. We chose the cecum because it is amenable to a quantitative analysis of its mobility, whereas other colonic segments can be evaluated only subjectively.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
|
|
|
|
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
|
Extrapolating this data, a change in axis of less than 30° in more than two planes corresponded to no diagnostic dilemma (sensitivity, 82% [9/11]; specificity 90% [19/21]). A change in axis of more than 60° in a single plane corresponded to a diagnostic dilemma (sensitivity, 100% [9/9]; specificity, 86% [18/21]).
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
A well-recognized cause of mistaking a polyp for feces is a pedunculated polyp—the longer the stalk, the greater the potential mobility of the head of the polyp. The correct diagnosis can be made if the stalk is appreciated when the polyp is on the nondependent surface or when shown on a 3D endoluminal view. However, apparent mobility can be caused when the colon itself moves and the lesion remains fixed in position creating the disturbing pitfall of mistaking colon mobility for lesion mobility [8]. Therefore, the reviewer may interpret the lesion as feces, especially if it lacks a mottled appearance or highly angulated margin. In fact, those two signs of feces must be used with caution because gas can be trapped between the colonic wall and a polyp, simulating feces. Likewise, adenomatous polyps can be irregular in shape, particularly as they enlarge.
Laks et al. [8, 9] found that 11 of 41 polyps 5 mm or larger appeared to move with gravity from one wall to the other. Five of the polyps were pedunculated and only six were sessile, the latter presenting a greater diagnostic dilemma. In this situation, the presence of the presumptive polyp on the nondependent surface suggests that the "lesion" is a polyp when, in fact, it might represent adherent feces. At least one of the sessile lesions shown by Laks et al. was located in the cecum.
The cecum, transverse colon, and sigmoid colon normally have a long mesentery and are therefore more likely to move than other segments of the colon. When evaluating these particular segments, the radiologist should pay special attention to discern colon movement by comparing the supine and prone views. It is often easy for the reviewer to determine the mobility of the colon by identifying landmarks including the fold pattern, concurrent diverticula, ileocecal valve, or appendix.
Many software programs provide a transparent view of the colon, simulating the appearance of a double-contrast barium enema. The overall length, tortuosity, and mobility of the colon are sometimes more easily discerned on these views than on the 2D view. The endoluminal 3D view and novel views that appear to cut the colon open and lay it flat (so-called virtual dissection or filet views) are least helpful in showing colonic mobility. The pitfall of confusing a polyp for feces due to mobility is most likely to occur in long, highly tortuous colons where comparison of the supine and prone views is tedious and time-consuming. The cecum in particular is highly variable in its location [10].
The advent of fecal tagging and digital subtraction bowel cleansing will potentially minimize the occurrence of this pitfall. However this pitfall will continue to be a concern since fecal tagging is not yet 100% effective because not all feces will tag well or completely. Therefore, any residual fecal material not tagged can be a potential problem. In addition, barium coating of a true colonic polyp is a major pitfall in solid-fecal tagging.
This pitfall is also relevant to a primary 3D endoluminal interpretation method. On the primary 3D view, when the reviewer sees a solid lesion it is still necessary to determine if the lesion has moved from prone to supine before characterizing it as either feces or a polyp. The difficultly with the primary 3D view is that it is easy to get disoriented, and what many software programs for CT colonography label as superior or inferior does not correlate precisely with the dependent or nondependent colon wall as the colon moves between the prone and supine patient positions. However, in the axial and multiplanar reconstruction views, there are anatomic landmarks to help prove how the colon moved.
Two-dimensional images will continue to remain important for correlation of lesions seen on 3D rendering. Two-dimensional images improve specificity and can distinguish true polyps from a variety of pseudopolyps (residual feces, impacted diverticula, extrinsic compression, and the ileocecal valve) seen on 3D imaging. For example, 3D images are not sensitive for the presence of gas within a lesion; therefore, 2D correlation is needed to identify a mottled appearance.
When interpreting CT colonography, one need not be concerned about colonic mobility in all cases. Only when a possible polyp is being studied and the decision rendered that the object is feces is based exclusively on its mobility and not its texture should the pitfall of colonic mobility be evaluated. One suggestion is to view a 3D double-contrast barium enema-like transparency view to quickly understand the overall configuration of the colon and compare the supine and prone views. This is often all that is necessary to evaluate a potentially mobile lesion when the colon is not overly tortuous.
When the colon is tortuous and there is much overlap of segments, a more detailed analysis of colonic mobility will require paging through the images to study the location of anatomic landmarks such as the cecal cap, the ileocecal valve, and the appendiceal origin. We have found that paging through the coronal plane is most helpful in rapidly recognizing mobility of the right colon. Mobility of the sigmoid colon, when tortuous, can be complex and require all multiplanar and 3D transparency views to problem solve. Other nonfixed anatomic landmarks, such as the fold pattern and number and location of diverticula relative to the potential lesions, can also be helpful clues.
A limitation of this study design is that the change in ileocecal-appendiceal axis does not directly correlate with the true movement of the colon because it is a 2D measurement in three planes. Again, the colon may undergo many complex translations in the x-, y-, and z-axes. However, the change in the ileocecal-appendiceal axis did give a general indication of how the colon moved and, therefore, gave more information than viewing the axial images exclusively.
We conclude that rotation of the cecum can be geometrically complex and occur in several planes. Although not all cases pose a diagnostic dilemma to the interpretation of CT colonography, our preliminary results suggest that cecal mobility can be an important pitfall and explains previous reports of this occurrence. We suggest that when solid feces is suspected in the cecum based on mobility, the reviewer should take the time to carefully analyze mobility of the cecum using multiplanar images.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  T. Mang, A. Maier, C. Plank, C. Mueller-Mang, C. Herold, and W. Schima Pitfalls in Multi-Detector Row CT Colonography: A Systematic Approach RadioGraphics, March 1, 2007; 27(2): 431 - 454. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
