Diverticular Disease

Diverticular disease is the most common colonic disease in the Western world, affecting 10-30% of people at age 50 years and 30-60% at age 80 years. However, the disease is asymptomatic in the majority of patients. Together with aging, longstanding low dietary fiber is the main predisposing factor for diverticular disease. Other etiological factors have been suggested, including increased consumption of red meat, fat, and salt.

An early stage of the disease is the so-called pre-diverticulosis, which is characterized by thickening

Table 13.1. CTC features of diverticular disease

Diverticula

Gas filled outpouching of colon wall in 2D Complete dark ring in 3D Cave: polypoid pseudolesion in VE "en face" Impacted diverticula

Polypoid pseudolesion in 3D Incomplete ring shadowing in 3D

2D Pathognomonic: filled with air, stool, retained barium, CM wall enhancement Diverticulitis Wall thickening with CM enhancement Stenosis and pericolic fat stranding VE: Nonspecific of the muscular layer, shortening of the taeniae, and luminal narrowing. With advancing disease, caliber and haustral abnormalities appear. This results in a global and regular wall thickening of >4 mm of long colonic segments with prominent semicircular folds, shortened interhaustral segments (concertina appearance), and a reduced colonic distensibility (Lefere et al. 2003) (Fig. 13.1a-c).

Most of the diverticula are pseudodiverticula, which are herniations of the mucosa, muscularis mucosae, and submucosa through the circular mus-cularis propria layer at weak points in the colonic wall where nutrient arteries penetrate the muscula-ris propria. Rarely, true diverticula (most often at the proximal colon) are found, which are characterized by an outpouching of mucosa, submucosa, and the muscularis propria. The radiological features of the two types of diverticula are not distinguishable. The CTC appearance of diverticula is easily recognized as air-filled outpouchings of the colonic wall on 2D images. On the virtual endoscopic (VE) images, the diverticular orificium can be recognized as a complete dark circumferential ring when seen en face. Because of the complete dark ring, diverticula may simulate polyps when seen en face on VE images (Fenlon et al. 1998) (Fig. 13.2a-c).

Differential diagnostic problems can occur if a diverticula inverts into the colonic lumen or is impacted with stool. A diverticulum may occasionally invert into the colonic lumen and produce a pseudopolypoid lesion on 2D and 3D images. The corresponding VE image is nonspecific and shows a polypoid lesion (Fig. 13.3a,b). The 2D images are essential to arrive at the correct diagnosis: inverted diverticula with pseudopolypoid shape sometimes contain some air, residual stool, or fat attenuation because of a central umbilication in the inverted part of the diverticulum, or due to an inclusion of perisigmoidal fat (Fenlon 2002).

A more common finding than inverted diver-ticula, diverticula impacted with fecal material may appear as a raised lesion and mimic polyps on VE images. On the 2D images, a hyperdense ring with a hypodense center containing air or stool, or even retained barium from prior examinations, can be found in such a lesion (Hara et al. 1997) (Fig. 13.4a,b).

Inflammation of the diverticula leads to symptomatic diverticulitis, which occurs in two-thirds of cases in the sigmoid colon. Complications that may develop are pericolic abscess, perforation, hemorrhage, fistula formation, and post-inflammatory stenosis. For diagnosis of acute diverticulitis, CT without colon distension is the primary imaging modality. Significant findings for diverticulitis are cone-shaped mild wall thickening with involvement of a long segment (>10 cm) with increased contrast enhancement, pericolic fat stranding, and fluid at the root of the mesentery (Fig. 13.5). The most important differential diagnosis for diverticulitis is colon cancer. In contrast, extensive wall thickening with short extension (<5 cm), especially with shoulder formation and pericolonic lymph nodes, is suspicious for neoplasms (Chintapalli et al. 1999).

Presently, CT colonography has no role in the diagnosis of acute diverticulitis, and, in addition, the distension of the colon may lead to perforation. In selected cases, CTC may help in the differential diagnosis between diverticulitis and cancer after the acute inflammatory episode has subsided.

Virtual Colonoscopy Diverticula

Fig. 13.1a-c. Diverticulosis: a axial planes show multiple gas-filled outpouchings of colon wall in nearly all parts of the colon (arrow); b VE shows complete dark rings (arrow); c global volume rendering views show the extent of the disease with reduced colonic distension (concertina appearance), especially in the sigmoid colon (arrow)

Fig. 13.1a-c. Diverticulosis: a axial planes show multiple gas-filled outpouchings of colon wall in nearly all parts of the colon (arrow); b VE shows complete dark rings (arrow); c global volume rendering views show the extent of the disease with reduced colonic distension (concertina appearance), especially in the sigmoid colon (arrow)

Fig. 13.2a,b. Polyp vs diverticula: a VE shows complete dark ring at the diverticulum (arrow); b incomplete ring shadowing at the polyp (arrow)

Fig. 13.3a,b. Inverted diverticulum: pseudopolypoid shape on virtual endoscopic images. On 2D images, these lesions contain some air, residual stool, or fat attenuation because of a central umbilication in the inverted part of the diverticulum or due to an inclusion of perisigmoidal fat. (Used with permission of Lefere et al. 2003)

Fig. 13.4a,b. Normal (arrow) and stool-impacted diverticulum (arrowhead). VE shows complete dark ring at the normal diverticulum and incomplete ring shadowing at the impacted diverticulum simulating a polypoid lesion. On 2D images in the impacted diverticulum, a hyperdense ring with a hypodense center can be found

Fig. 13.5a,b. Diverticulitis axial unen-hanced (a) and curved multiplanar view with IV contrast (b): Wall thickening of a long segment (arrow) with CM enhancement, diverticula, stenosis, and fat stranding

Fig. 13.2a,b. Polyp vs diverticula: a VE shows complete dark ring at the diverticulum (arrow); b incomplete ring shadowing at the polyp (arrow)

Diverticulosis Diverticulitis

Fig. 13.3a,b. Inverted diverticulum: pseudopolypoid shape on virtual endoscopic images. On 2D images, these lesions contain some air, residual stool, or fat attenuation because of a central umbilication in the inverted part of the diverticulum or due to an inclusion of perisigmoidal fat. (Used with permission of Lefere et al. 2003)

Thickening Strandin Bowel Wall

Fig. 13.5a,b. Diverticulitis axial unen-hanced (a) and curved multiplanar view with IV contrast (b): Wall thickening of a long segment (arrow) with CM enhancement, diverticula, stenosis, and fat stranding

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