Polyps

Polyps maybe sessile, pedunculated, or flat (i.e., with the base measuring more than twice that of the height). Sessile polyps will possess polypoid morphology on axial, 2D multiplanar reformatted, and 3D endoluminal views (Fig. 14.23). When sessile polyps are of sufficient size (generally consid-

Virtual Colonoscopy

Fig. 14.18a-c. A suspicious filling defect on 2D images (a, arrow) demonstrates sharp intraluminal projections on 3D endoluminal images (b) and is not of soft tissue attenuation (c). These features indicate the lesion represents stool

Fig. 14.18a-c. A suspicious filling defect on 2D images (a, arrow) demonstrates sharp intraluminal projections on 3D endoluminal images (b) and is not of soft tissue attenuation (c). These features indicate the lesion represents stool b a c

Virtual Colonoscopy
Fig. 14.19a,b. Cecal fluid redistributes between supine (a) and prone (b) imaging (arrows). When there is excessive fluid, intravenous contrast can be used to enhance submerged lesions. Note the dependent position of the fluid
Colonoscopy Pathology
Fig. 14.20a-d. Fluid can be seen on 3D endoluminal images (a, arrow) and on virtual pathology (b, arrow) as filling defects, Axial 2D image demonstrates an air-fluid level (c, arrow) and soft tissue setting shows that the filling defects not have soft tissue attenuation (d, arrow)

ered to be three times the slice thickness), they will also possess internal soft tissue attenuation. Sessile polyps are generally seen on both supine and prone views, but about 10-15% of medium-sized polyps will be seen only in one view, due to suboptimal distention, stool or fluid in the same colonic segment in the complementary position. Lesions that appear as sessile polyps in one position should not be disregarded unless the same segment is optimally seen in the corresponding position.

Pedunculated polyps possess a stalk and a head. They are best seen on 2D axial and images (Fig. 14.24). Using 3D endoluminal renderings, the stalk of a pedunculated polyp is often inseparable from the colonic wall. Polyps with long stalks maybe missed at CT colonography, as the larger filling defect representing the head of the polyp may appear to move between colonic segments (Fenlon et al. 1999). Careful interrogation of suspicious filling defects for a stalk connecting them to the colonic wall is imperative in diagnosing pedunculated polyps. In our experience, pedun-culated polyps can be found with a high degree of accuracy.

Flat lesions can be difficult to visualize both endo-scopically and radiographically. On CT, flat lesions appear as focal regions of colonic wall thickening with soft tissue attenuation. Flat lesions are often cigar-shaped, and are best seen on 2D axial and MPR images with narrow window settings (such as bone window settings) (Fidler et al. 2002). Perturbation in the colonic wall can be visualized when surveying the colon with 2D images using lung windows, and when these perturbations are discovered, interrogation of soft tissue window settings is imperative (Fig. 14.25). Similar perturbations can often be seen on 3D endoluminal views, but can be occult. Like other polyps, flat lesions are usually seen in both the supine and prone views, unless the segment in which the lesion is located is suboptimally visualized in one of the views. Intravenous contrast can be useful in characterizing flat lesions. Flat lesions should not

Virtual Colonoscopy

Fig. 14.21a-d. Compression by one of the iliac arteries in this case has resulted in a linear extrinsic compression on the sigmoid colon that is well demonstrated on 3 D endoluminal view (a, arrows) and virtual pathology (b, arrow). 2D axial images demonstrates the extrinsic nature of these lesions (c,d, arrows)

Fig. 14.21a-d. Compression by one of the iliac arteries in this case has resulted in a linear extrinsic compression on the sigmoid colon that is well demonstrated on 3 D endoluminal view (a, arrows) and virtual pathology (b, arrow). 2D axial images demonstrates the extrinsic nature of these lesions (c,d, arrows)

Virtual Colonoscopy
Fig. 14.22a-c. Motion artifacts cause image blur on axial images (a), but are best appreciated using 2D oblique coronal or sagittal images, which show luminal incongruity along Z-axis of the colon, (b,c, arrows)
Virtual Colonoscopy

Fig. 14.23a-c. Sessile polyp: a supine 2D axial image and; b 3-D endoluminal view demonstrate a polypoid filling defect in the ascending colon; c after changing to soft tissue window setting , the homogenous soft tissue attenuation of the lesion is demonstrated. Colonoscopy demonstrated a 1.5 tubulovillous adenoma

Fig. 14.23a-c. Sessile polyp: a supine 2D axial image and; b 3-D endoluminal view demonstrate a polypoid filling defect in the ascending colon; c after changing to soft tissue window setting , the homogenous soft tissue attenuation of the lesion is demonstrated. Colonoscopy demonstrated a 1.5 tubulovillous adenoma a

Virtual Colonoscopy
Colonoscopy Images Polyps Adenomas
d

Fig. 14.24a-e. Pedunculated polyp: a supine 2D axial image and; b prone 2D axial image show a polyp in the descending colon associated with a stalk (arrowhead); c soft tissue window setting shows the head of the polyp to be of soft tissue attenuation. Note that the lesion changes position to the dependent position due to its long stalk; d,e endoluminal appearances of the pedunculated polyp c e

Colonoscopy Positioning

Fig. 14.25a-c. Flat cancer prone view: a 2D axial image and: b multiplanar reformatted image show a focal region of soft tissue thickening along the lateral aspect of the ascending colon lying along a haustral fold. Soft tissue window settings show the soft tissue attenuation of the lesion (arrows); c on 3-D views the lesion appears as a focal thickening along a haustral fold (arrow)

Fig. 14.25a-c. Flat cancer prone view: a 2D axial image and: b multiplanar reformatted image show a focal region of soft tissue thickening along the lateral aspect of the ascending colon lying along a haustral fold. Soft tissue window settings show the soft tissue attenuation of the lesion (arrows); c on 3-D views the lesion appears as a focal thickening along a haustral fold (arrow)

be confused with luminal collapse. The colonic wall does thicken as it collapses. The thickened colonic wall can be distinguished from the true flat lesion in that it is not well defined, should be distended in the corresponding position, and smoothly taper to a normal thickness in adjacent areas of appropriate distention (Fig. 14.7). The term "flat lesion" can represent a variety of pathologies, from flat adenomas to hyperplastic lesions to tubulovillous adenomas and flat carcinomas. In general, flat lesions tend to be more advanced lesions.

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Responses

  • Amira
    What is suboptimal distention sigmoid colon?
    8 years ago

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