Bowel wall thickening at CT: simplifying the diagnosis
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In this article we present a simplified algorithm-based approach to the thickening of the small and large bowel wall detected on routine computed tomography (CT) of the abdomen.
Thickening of the small or large bowel wall may be caused by neoplastic, inflammatory, infectious, or ischaemic conditions. First, distinction should be made between focal and segmental or diffuse wall thickening. In cases of focal thickening further analysis of the wall symmetry and perienteric anomalies allows distinguishing between neoplasms and inflammatory conditions. In cases of segmental or diffuse thickening, the pattern of attenuation in light of clinical findings helps narrowing the differential diagnosis.
Focal bowel wall thickening may be caused by tumours or inflammatory conditions. Bowel tumours may appear as either regular and symmetric or irregular or asymmetric thickening. When fat stranding is disproportionately more severe than the degree of wall thickening, inflammatory conditions are more likely. With the exception of lymphoma, segmental or diffuse wall thickening is usually caused by benign conditions, such as ischaemic, infectious and inflammatory diseases.
• Thickening of the bowel wall may be focal (<5 cm) and segmental or diffuse (6-40 cm or >40 cm) in extension.
• Focal, irregular and asymmetrical thickening of the bowel wall suggests a malignancy.
• Perienteric fat stranding disproportionally more severe than the degree of wall thickening suggests an inflammatory condition.
• Regular, symmetric and homogeneous wall thickening is more frequently due to benign conditions, but can also be caused by neoplasms such as well-differentiated adenocarcinoma and lymphoma.
• Segmental or diffuse bowel wall thickening is usually caused by ischaemic, inflammatory or infectious conditions and the attenuation pattern is helpful in narrowing the differential diagnosis.
KeywordsComputed tomography Inflammatory bowel disease Small bowel intestinal neoplasms
With the development of multidetector computed tomography scanners (MDCT), computed tomography became an important tool in the detection and characterisation of bowel abnormalities. This technology makes possible the acquisition of isotropic data and affords the capability of performing high-resolution multiplanar reconstructions [1, 2, 3, 4, 5, 6]. In particular, CT enterography acquired after luminal distention through the administration of high volumes of neutral contrast material (,1500-2,000 ml of water, water-methylcellulose solution, polyethylene glycol electrolyte solution or low-concentration barium) is helpful in displaying the thickness and mural enhancement of the small bowel wall . Adequate preparation and distention of the bowel lumen is, however, not always possible in the acute setting. In addition, wall abnormalities of the small and large bowel may be incidentally detected in asymptomatic patients or in patients with nonspecific complaints. For these, the CT imaging technique applied in a significant proportion of patients is a conventional one and radiologists should have a high level of suspicion in the detection and interpretation of bowel wall abnormalities.
Normal bowel wall
Acceptable bowel wall thickness values on CT strongly depend on the degree of bowel distension and vary widely in the literature. Some agreement, however, exists that the small bowel wall should not exceed 3 mm despite luminal distention, and the colonic wall can vary from 1 to 2 mm when the lumen is well distended to 5 mm when the wall is contracted or the lumen is collapsed [2, 3, 4, 5, 6, 7, 8, 9].
The bowel wall normally enhances after the administration of intravenous contrast material. The mucosa is the most intensely enhancing layer of the bowel wall and when enhanced may appear as a distinct layer. In contrast, the submucosa is less vascularised and is seldom seen as a separate structure on CT scans unless it is oedematous, haemorrhagic or infiltrated by fat .
Thickening of the bowel wall
Thickening of the bowel wall may be caused by several pathologic conditions or be a normal variant . When thickening of the bowel wall is identified on CT, several imaging features must be assessed in order to narrow the differential diagnosis: length of involvement, degree of thickening, symmetric versus asymmetric involvement, pattern of attenuation and perienteric abnormalities [3, 4, 6]. Each of these features may have a different significance according to the acute or chronic onset of clinical symptoms and will be further discussed in an algorithm approach .
Approach to the thickened bowel wall
Focal thickening of the bowel wall
Thickening of the bowel wall is considered focal when it extends less than 5 cm [3, 11]. Focal thickening may be caused by tumours or by inflammatory conditions, and distinguishing between the two conditions should be attempted. In addition to the clinical presentation, analysis of the wall symmetry, degree of thickening and perienteric abnormalities provides additional information for the correct diagnosis. In the setting of focal wall thickening three main scenarios may occur: (1) asymmetric focal thickening, (2) symmetric focal thickening and (3) perienteric abnormalities (fat stranding) disproportionately greater than the degree of wall thickening.
(1) Asymmetric focal thickening of the bowel wall
In this setting the attenuation pattern of the bowel wall after intravenous contrast administration and the perienteric abnormalities may be helpful in establishing the diagnosis. Contrast enhancement of malignant bowel tumours is frequently heterogeneous with areas of low attenuation due to ischaemia and necrosis [4, 10, 11]. This is particularly common on large and high-grade poorly differentiated tumours such as adenocarcinoma and stromal cell tumours . In addition, regional adenopathy and distant metastases, when present, support the diagnosis .
Although asymmetric and heterogeneous focal thickening of the bowel wall usually indicates a malignancy, benign inflammatory conditions such as intestinal tuberculosis and Crohn’s disease may present with similar imaging features, sometimes mimicking neoplasms [3, 14, 15].
In addition, thoracic features of tuberculosis and other abdominal signs of involvement such as findings of peritonitis and hepatosplenic dissemination support the diagnosis.
(2) Symmetric focal thickening of the bowel wall
(3) Perienteric abnormalities (fat stranding) disproportionately greater than the degree of bowel wall thickening
Inflammatory or infectious diseases of the bowel are usually centred in the bowel wall and can cause segmental or diffuse wall thickening . However, in a few inflammatory enteric or perienteric conditions, the inflammatory changes are more prominent in the mesentery adjacent to the bowel rather than in the bowel wall itself. In these conditions, the bowel involvement is usually focal and mild, and the fat stranding is disproportionately greater than the degree of wall thickening. This is a helpful clue in narrowing the differential diagnosis to mainly four conditions: diverticulitis, epiploic appendagitis, omental infarction and appendicitis .
Diverticulae are sacculations of the mucosa and submucosa through the muscularis of the bowel wall, which are more common in the descending and the sigmoid colon. Diverticulitis occurs when the neck of a diverticulum becomes occluded, resulting in microperforation and pericolonic inflammation.
Carcinoma of the colon is the most important differential diagnosis of diverticulitis when the wall thickening is more pronounced. The inflamed diverticula, homogeneous bowel wall enhancement, mesenteric signs of inflammation and lack of lymph nodes in light of the acute clinical presentation—localised pain and fever—support the diagnosis [18, 19].
Epiploic appendages are pedunculated adipose structures protruding from the serosa surface of the colon into the peritoneal cavity. Acute epiploic appendagitis results from the torsion or venous occlusion of the epiploic appendage and is more frequent in the sigmoid colon .
Segmental or diffuse bowel wall thickening
In the setting of segmental or diffuse bowel wall thickening, one of three attenuation patterns after intravenous contrast administration may occur: a stratified attenuation pattern, white attenuation pattern or grey attenuation pattern [4, 6, 21].
Stratified pattern of attenuation
In this pattern, two (double halo sign) or three (the target sign) concentric and symmetric layers of alternating densities are recognised on the thickened bowel wall after intravenous contrast administration.
This pattern indicates inflammation or ischaemia of the bowel where the inner and outer high-density layers correspond to the hyperemic mucosa and serosa, respectively, while the low-density layer presumably represents the oedematous submucosa [2, 3, 4, 6, 7, 11, 21].
Although generally indicative of benign conditions, these signs are not specific and may be present in several acute conditions. Clinical presentation and adjacent findings such as perienteric findings help in narrowing the differential diagnosis:
Thickening of the bowel wall is the most common but least specific CT sign of bowel ischaemia [5, 22]. The extent of involvement, degree of thickness and pattern of attenuation of the ischaemic bowel vary according to three main factors: (1) pathogenesis of the ischaemia (arterial-occlusive, veno-occlusive or hypoperfusion); (2) severity of the ischaemia (transient ischaemia of the mucosa and/or submucosa versus transmural bowel wall necrosis); (3) superimposed haemorrhage or infection .
Although bowel wall thickening is a common finding in cases of bowel ischaemia, the ischaemic bowel wall may also appear paper thin, particularly in cases of acute arterial occlusion .
Idiopathic inflammatory bowel disease
By contrast, UC is typically left sided, involves the rectum in 95 % of cases, and shows contiguous, circumferential and proximal extension through the colon . The inflammatory process in UC is superficial, predominantly affecting the mucosa . Thus, wall thickening and pericolonic involvement are not as extensive in ulcerative colitis as they are in Crohn’s disease .
Infectious enteritis or colitis and pseudomembranous colitis
In most cases of infectious enteritis the small bowel wall appears normal or mildly thickened . By contrast, infectious colitis typically manifests with significant wall thickening, which may demonstrate either homogeneous enhancement or a striated pattern due to intramural oedema. Stranding of the pericolic fat and ascites are also commonly seen [7, 28, 29]. Although the affected portion of the colon may suggest a specific organism, there is a considerable overlap of the appearances. Thus, laboratory studies are needed to achieve a definitive diagnosis .
Specific clinical entities
Other causes of stratified appearance
Stratification of the bowel wall may also be caused by infiltration of the submucosa by tumour or fat. The rare infiltrating scirrhous carcinomas (linitis plastica) of the stomach or rectosigmoid may present with symmetric wall thickening, regular contours and stratification of the bowel wall [4, 11]. Narrowing of the intestinal lumen, regional adenopathy and distant metastasis point to the correct diagnosis .
White pattern of attenuation
The white pattern is caused by intense enhancement of the bowel wall when its density is equal to or greater than that of venous vessels in the same scan . Visual assessment is usually sufficient to detect hyperenhancement of the wall when the bowel lumen is well distended . This pattern can be seen mainly in two clinical entities: ischaemia and inflammatory bowel disease.
Hyperenhancement of the ischaemic bowel may occur because of the hyperaemia (i.e. mesenteric venous occlusion with outflow obstruction) or hyperperfusion (i.e. reperfusion after occlusive or nonocclusive ischaemia) of the bowel wall and is a good prognostic factor, indicating viability of the bowel wall [5, 22, 25]. As referred to above, associated imaging findings of bowel ischamia include occlusion of the mesenteric vessels, bowel dilatation, mesenteric oedema and ascites [3, 11, 22, 23, 26].
Grey pattern of attenuation
The grey pattern of attenuation indicates mild to diminished enhancement of the bowel wall and is considered when the attenuation of the bowel wall is similar to that of the muscle on contrast-enhanced scans . In general this pattern corresponds to the least specific of the attenuation categories and so other imaging findings and clinical presentation are essential in establishing the correct diagnosis .
In patients with chronic Crohn’s disease or chronic radiation enteritis, involved bowel loops may show diminished enhancement due to the development of transmural fibrosis [3, 4, 6]. Once transmural fibrosis has developed in Crohn’s disease, mural stratification is no longer seen. In this context, homogeneous low attenuation of the bowel indicates quiescence of the disease.
Chronic radiation enteritis or colitis may develop 6-24 months after completion of radiation therapy. Distribution is related to treatment fields and most frequently involves the rectum and sigmoid because of radiation for pelvic disease (most commonly prostatic or cervical cancer) . CT findings of chronic radiation enteritis include hypoenhancing wall thickening, increased pelvic fat and thickening of the perienteric fibrous tissue . Strictures and fistulas may also occur .
Bowel wall thickening may be focal and segmental or diffuse. In cases of focal thickening, the degree and symmetry of thickening and perienteric abnormalities help narrow the differential diagnosis: while heterogeneous and asymmetric focal thickening is usually associated with malignancies, symmetric regular and homogeneous thickening may be caused by benign conditions but also well-differentiated tumours. Disproportionate fat stranding compared to the degree of wall thickening suggests inflammatory conditions. Segmental or diffuse bowel thickenings are usually caused by benign conditions, with the exception of lymphoma. Common causes include ischaemia, inflammatory and infectious conditions. The pattern of attenuation helps narrow the differential diagnosis of segmental or diffuse wall thickening but still there is a significant overlap on CT imaging findings of different non-neoplastic bowel conditions.
- 1.Fernandes TC, Castro R, Pinto D, Oliveira MI, Carneiro A, Cunha R (2011) Bowel wall thickening – a complex subject made simple. Electronic Poster presented at 2011 ESGAR meeting doi: 10.5444/esgar2011/EE-063#_blank
- 15.Balthazar EJ, Gordon R, Hulnick D (1990) Ileocecal tuberculosis: CT and radiologic evaluation AJR. Am J Roentgenol 154:449–503Google Scholar
- 33.Bodily KD, Fletcher JG, Solem CA, Johnson CD, Fidler JL, Barlow JM, Bruesewitz MR, McCollough CH, Sandborn WJ, Loftus EV Jr, Harmsen WS, Crownhart BS (2006) Crohn disease: mural attenuation and thickness at contrast-enhanced CT Enterography-correlation with endoscopic and histologic findings of inflammation. Radiology 238(2):505–516PubMedCrossRefGoogle Scholar
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