Practical CT Techniques

It is important to first distinguish abnormal from normal segments. As discussed below, differential contrast enhancement is a cardinal sign of many small bowel pathologies. Indeed, an abnormal segment will often be initially perceived owing to the presence of a hyperenhancing mass or focus of wall thickening. However, it is important to be aware that during the enteric phase of enhancement the jejunum enhances more than the ileum Figure 1 [ 2 , 18 ].

This should not be mistaken for pathology. Furthermore, collapsed bowel loops appear to enhance more than the distended loops in the same segment Figure 2 [ 2 , 18 , 19 ]. In the non-distended loops, other signs of disease must be used to diagnose pathological processes, including associated changes in the adjacent small bowel mesentery such as hypervascularity, fat stranding or lymphadenopathy.

Coronal CT enterography image showing normal jejunal short arrows and ileal long arrrows loops. Note the prominent mucosal pattern in the proximal jejunal loops. Axial CT enterography image showing a collapsed small bowel mimicking pathology long arrow compared with a normal fluid-filled loop short arrow. Note the absence of any associated changes.

Focal small bowel spasm is frequently encountered, despite the use of Buscopan, and can mimic short strictures. Identification of similar areas of spasm, lack of mucosal hyperenhancement and absence of mesenteric abnormality helps to distinguish spasm from true pathology Figure 3.

Repeat scanning through the section of interest is often useful to distinguish stricture from a collapsed loop, but clearly the dose of ionising radiation imparted by CT makes this less applicable than during MRI enterography. As noted above, multiplanar reformatting when reporting CT enterography has been shown to increase diagnostic confidence and sensitivity.

Axial CT enterography image showing two areas of focal small bowel spasm mimicking pathology arrows. The stomach and colon are frequently well distended and merit careful evaluation for associated pathology. However, it is important to recognise the limitations of colonic review in the absence of formal laxative preparation and dual patient positioning. Key tips and pitfalls are summarised in Table 2. The differential diagnosis for abnormal small bowel is wide. A more detailed description of the commoner small bowel diseases is provided below.

However, when interpreting CT enterography, it is important to be aware of the more general diagnostic principles, which govern the correct interpretation of small bowel abnormalities. Target appearance with stratification of the layers of the small bowel wall mural stratification is generally found with benign conditions—for example, vasculitis, Crohn's disease, venous thrombosis with associated bowel oedema or ischaemia and intramural haemorrhage. If wall enhancement is homogeneous and mild i.

Homogeneous hyperenhancement is commonly seen with active Crohn's disease, and is frequently associated with increased density in the surrounding mesenteric fat.

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Indeed, it has been proposed by Bodily et al [ 22 ] that a cut off of HU can be used with reasonable accuracy to diagnose activity in Crohn's-afflicted small bowels. Heterogeneous enhancement is seen in small bowel neoplasms, including gastrointestinal stromal tumours, adenocarcinomas, metastases and peritoneal deposits. Decreased enhancement is typical of bowel ischaemia [ 16 , 23 - 25 ], and usually precedes the development of intramural gas and subsequent perforation.

For the purpose of differential diagnosis, the length of small bowel involvement can be divided into three: Focal small bowel wall thickening is generally found with neoplasms, endometriosis, small bowel diverticulitis, foreign body perforations, small bowel ulcers secondary to non-steroidal anti-inflammatory drugs and occasionally granulomatous processes like tuberculosis and Crohn's disease [ 16 , 26 - 30 ].

Segmental involvement is found with intramural haemorrhage, Crohn's disease, lymphoma, infectious enteritis and ischaemia, particularly due to superior mesenteric artery SMA embolus or superior mesenteric vein SMV thrombosis [ 16 , 22 , 31 - 34 ]. In a patient with previous malignancy and segmental involvement, previous radiotherapy should be considered [ 16 , 35 ]. Diffuse involvement of the small bowel is commonly a result of hypoalbuminaemia, low-flow intestinal ischaemia, vasculitis, graft vs host disease and infectious enteritis [ 16 , 22 , 30 , 36 - 38 ].

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The site, degree and symmetry of mural thickening can also help in the characterisation of small bowel pathology. Tables 3 — 5 summarise mural thickening [ 16 , 22 , 30 , 31 , 39 - 41 ], symmetry of small bowel thickening [ 16 , 31 , 42 ] and sites of abnormality in the small bowel [ 16 , 41 ], respectively. Identification of the layer of the small bowel wall that is predominantly affected also helps in reaching a diagnosis Table 6.

The mucosa is seen to be predominantly affected in inflammatory conditions like Crohn's disease, tuberculosis and neoplasms such as adenocarcinoma. Although mucosa is affected predominantly in infectious conditions and vasculitides, mucosal disruption is not evident on MDCT in these conditions [ 16 ]. The predominant abnormality is seen in the submucosa in conditions like intramural haemorrhage, vasculitis, ischaemia, hypoalbuminaemia and angio-oedema. In conditions where there is thickening of the submucosa, the equivalent barium follow-through appearance is classically described as stacked coin- or picket fence-like.

The serosa is predominantly involved in metastases, endometriosis, carcinoid and other inflammatory conditions in the peritoneum. One of the major advantages of CT and other cross-sectional techniques is their ability to visualise the extraluminal soft tissues. It is therefore important to carefully evaluate the structures beyond the bowel wall. Patency or otherwise of mesenteric blood vessels should be assessed to exclude a vascular pathology such as arterial embolus or venous thrombosis. Lymphadenopathy in the mesentery can give an important clue to the presence of underlying disease, both benign and malignant.

In intestinal tuberculosis, for example, the lymph nodes have a central low attenuation, while in lymphoma and Crohn's disease the nodes are usually of soft tissue density. Presence of other extraluminal findings such as mesenteric oedema, fluid, fibro-fatty proliferation, abscess and fistula should also be carefully assessed. A list of common indications for CT enterography is given in Table 7. CT enterography provides a highly accurate method for diagnosis and assessment of Crohn's disease in adults.

Initial diagnosis in combination with endoscopic biopsy where possible or exclusion of all but subtle or early disease can often be made with high reader confidence. In addition, a single examination can assess severity, extent and location of disease, coupled with extraluminal manifestations and complications. The radiation exposure associated with CT is discussed in greater detail below. However, with increasingly robust MR enterography and ultrasound techniques available, it is the responsibility of radiologists and clinicians alike to ensure that cumulative radiation dose is strongly considered when selecting the optimal imaging modality for assessment of Crohn's disease.

Consideration must be made as to the age of the patient, their past diagnostic history, previous imaging and endoscopic examinations and general well-being, as well as the specific clinical question and availability of imaging platforms and interpretative radiological expertise. A recent survey of use of small bowel imaging of Crohn's disease within National Health Service radiological practice showed that although CT is relatively infrequently used as a first-line test in younger patients without a prior diagnosis, it is commonly performed in those with suspected extraintestinal complications [ 43 ].

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Radiological findings of Crohn's disease at CT enterography include mucosal hyperenhancement, mural thickening and stratification, transmural ulceration, mesenteric inflammation, engorgement of vasa recta and strictures associated with upstream dilatation Figure 4. Spectrum of findings in active Crohn's disease. Coronal CT enterography image showing mural thickening and mucosal hyperenhancement long arrows.

Compare the normal enhancement of the unaffected small bowel short arrow. Note the presence of enlarged mesenteric lymph nodes. Mucosal hyperenhancement refers to the increase in attenuation of mucosa relative to adjacent normal loops, and correlates well with the activity of Crohn's disease [ 2 , 19 ]. Mural stratification describes the visible layers of the inflamed small bowel wall demonstrated following administration of intravenous contrast in the enteric phase.

The mucosa and serosa enhance avidly, but the intervening bowel wall enhances to a varying degree, either due to intramural oedema isodense with water , indicating active disease [ 2 ], or intramural fat, indicating chronic inflammation. Intramural soft tissue attenuation may also indicate an inflammatory infiltrate Figure 5.

Such ulcers may penetrate through the wall, forming a small periluminal abscess indicating localised perforation. Different types of mural stratification. Crohn's disease predominantly involves the mesenteric border of the small bowel, frequently leading to asymmetric inflammation and fibrosis, with pseudosacculation of the antimesenteric border.

Pre-stenotic dilatation helps define, locate and assess the functional significance of a stricture. The usefulness of this sign in day-to-day clinical practice is debatable, however. Fibro-fatty proliferation of mesentery adjacent to diseased segments occurs, and usually persists into clinically inactive phases of the disease [ 2 , 44 ]. This mesenteric fat change, which manifests as abnormal loop separation on contrast examination, is easily appreciated at CT enterography Figure 4c.

Complications of Crohn's disease may be due to transmural ulceration as noted above , resulting in abscesses, or formation of fistulae between bowel segments and other organs commonly the anterior abdominal wall, vagina or renal tract; Figure 6. Metabolic changes are associated with the formation of gallstones and renal calculi, and less commonly CT enterography may reveal complicating tumours lymphoma, adenocarcinoma , sacroilitis or sequelae of sclerosing cholangitis. Complications of Crohn's disease: Axial CT enterographic image demonstrating the presence of a retroperitoneal abscess long arrow and a sinus tract short arrow connecting the abscess and the inflamed distal ileum.

The high spatial resolution of CT enterography, together with its relative insensitivity to motion and breathing artefacts, arguably make it more suitable for the detection of small bowel tumours than MR enterography. Pilleul et al [ 45 ], for example, reported a sensitivity of Table 8 lists the commoner small bowel tumours, and provides information on incidence and imaging characteristics. In the authors' experience, small bowel tumours are most commonly detected in patients with:.

Coronal CT enterography image demonstrates an exoenteric gastrointestinal stromal tumour of the jejunum arrow. Again, the usual high image quality of CT enterography makes it superior to MRI enterography for the investigation of chronic blood loss. Importantly, there are data suggesting that CT may be complimentary to capsule endoscopy. Eight of these patients were confirmed to have positive findings on capsule endoscopy or subsequent clinical diagnosis, and CT enterography identified three lesions, which were undetected on capsule endoscopy [ 47 ]. As noted above, multiphase CT scanning may increase the diagnostic yield in those with occult gastrointestinal bleeding, but consideration must be given to the increased radiation dose, particularly in the non-acute setting.

Practical CT Techniques - Wladyslaw Gedroyc, Sheila Rankin - Google Книги

In older patients, the risk-to-benefit ratio is decreased significantly and therefore multiphase CT enterography may be appropriate in the non-emergency situation where active bleeding is suspected. Finally, CT enterography has a definite role in the localisation of symptomatic bleeding —for example, in Meckel's diverticulum Figure 8 , which tends to present in younger patients.

However, when symptomatic, it is more often in male patients. Clinical symptoms arise from complications of Meckel's diverticulum, such as peptic ulceration with haemorrhage, diverticulitis, intestinal obstruction from diverticular inversion, volvulus, intussusception, inclusion of diverticulum in a hernia, formation of enteroliths and development of neoplasia within the diverticulum.

Meckel's diverticulum with ectopic gastric mucosa in a year-old male with gastrointestinal bleeding. Coronal CT enterography image showing a blind-ending gas-filled tubular structure with thickened, hyperenhancing mucosa in the left lateral margin arrows, with nodule identified by shorter arrow. CT enterography has several advantages over small bowel follow-through and conventional enteroclysis [ 1 , 15 ].

It can demonstrate extraluminal pathology in addition to luminal disease; the entire small bowel can be inspected, unhindered by overlapping loops; and use of multiplanar reconstructions are routine, increasing diagnostic accuracy and confidence [ 2 ]. As a result, a single CT enterography may eliminate the need for multiple radiological tests, thus improving diagnostic and cost efficiency, improving patient compliance and ultimately reducing radiation dose [ 1 ].

Fluoroscopic small bowel studies still hold advantages over cross-sectional techniques when assessing small bowel motility and patency of sinus or fistula tracts. There are limited published data comparing CT enteroclysis and CT enterography, but quality of luminal distension and patient experience are major considerations. However, a smaller study performed by Wold et al [ 8 ] showed no significant difference in distension between CT enteroclysis and enterography.

Intuitively, it would seem the quality of distension is linked to diagnostic accuracy, although there is no good evidence for this. CT enterography is more efficient, and probably preferred by patients owing to the absence of a nasoduodenal tube and shorter examination times , but further studies will help compare differences in examination quality, patient experience and diagnostic impact. Compared with MRI enterography, the authors of this article have found that CT enterography images frequently provide greater diagnostic confidence for exclusion of both small bowel and extraluminal pathology.

CT has superior spatial and temporal resolution, and fast single breath-hold examinations facilitate luminal navigation. CT is also cheaper and more available than MRI enterography, and patients benefit from shorter examination times and avoid MRI-associated claustrophobia. Gadolinium-based intravenous contrast used for MR examination may also be safer in adults than the iodinated contrast used for CT.

Nevertheless, a meta-analysis by Horsthuis et al [ 52 ] and a study by Siddiki et al [ 53 ] showed that small bowel CT and MRI had similar diagnostic performance. In addition, capsule endoscopy may be superior to radiological tests for diagnosis of early Crohn's disease and small bowel neoplasms.

Indeed, in circumstances where there is a high suspicion of underlying small bowel mucosal disease, capsule endoscopy provides an excellent complementary role [ 55 ]. However, capsule endoscopy is unable to assess the extramucosal manifestations or complications of disorders affecting the small bowel; for example, small bowel Crohn's disease is well recognised as a disease of both mucosa and mesentery, with variable involvement of both components. In addition, mucosal visualisation is frequently incomplete at capsule endoscopy and potentially adverse complications of capsule retention or, rarely, capsule endoscope aspiration can occur [ 55 ].

Radiological investigations are therefore preferred in patients with suspected small bowel stricture or established Crohn's disease. Unlike MR enterography or capsule endoscopy, CT enterography utilises ionising radiation. Brenner and Hall [ 55 ] predicted that 1.

Recently published data on the risk of carcinogenesis in adult patients due to CT quote significantly lower-risk percentages of 0. The effective dose will be higher in paediatric patients [ 58 ] and, because younger patients are more likely to require more scans during their lifetime, serious consideration should be given to the use of small bowel MRI in younger patients over CT. The authors believe that CT enterography is an appropriate technique when used judiciously in the right patient groups. Recent development of innovative techniques such as the adaptive statistical iterative reconstruction algorithm are promising and will probably provide diagnostic-quality CT images at significantly reduced radiation doses in the near future [ 58 ].

Wide availability of multidetector row CT platforms and examination efficiency with good patient tolerance will ensure a significant role for CT enterography, but this must be tempered with careful monitoring of the cumulative radiation dose. National Center for Biotechnology Information , U. Journal List Br J Radiol v. Author information Article notes Copyright and License information Disclaimer.

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This article has been cited by other articles in PMC. Abstract CT enterography is a new non-invasive imaging technique that offers superior small bowel visualisation compared with standard abdomino-pelvic CT, and provides complementary diagnostic information to capsule endoscopy and MRI enterography. Technique The technique of CT enterography combines small bowel distension with a neutral or low-density oral contrast mixture and abdomino-pelvic CT examination during the enteric phase following administration of intravenous contrast. Recommended protocol Table 1 provides a summary of the technique used in our institution, which has evolved over 4 years and CT enterography examinations.

Table 1 Summary of technique. Avoid solid foods clear liquids only for 4 h 20 ml 5 mg 5 ml —1 of oral metoclopromide is given at the start of the oral contrast agent Rosemont Pharmaceuticals Ltd, Leeds, UK — ml of neutral contrast see main text orally over 45 min 20 mg Buscopan administered intravenously immediately prior to scanning 20 mg ml —1 of hyoscine butylbromide; Boehringer Ingelheim Ltd, Bracknell, UK ml of Iohexol Omnipaque ; Amersham Health, Amersham, UK administered intravenously at 4 ml s —1 via an guage cannula.

Supine single phase images acquired at 50 s post-intravenous contrast administration slice CT scanner Brilliance CT; Philips Medical Systems, Best, the Netherlands Slice thickness of 2 mm with reconstruction interval of 0. Open in a separate window. Variations to the basic protocol-multiphase scan In patients where active gastrointestinal bleeding is suspected and endoscopic work-up is negative a multiphase scan protocol can be used to identify sites of occult gastrointestinal bleeding.

Table 2 Key tips. Improve bowel distension by active supervision and encouragement of oral contrast intake Carefully navigate the lumen Use a multiplanar review Differential contrast enhancement of the bowel is a cardinal sign The jejunum enhances more than the ileum Collapsed bowel loops and focal small bowel spasm can mimic pathology the; look for associated changes. Characterisation of small bowel pathology General principles The differential diagnosis for abnormal small bowel is wide.

Length of small bowel involvement For the purpose of differential diagnosis, the length of small bowel involvement can be divided into three: Mural thickening and symmetry The site, degree and symmetry of mural thickening can also help in the characterisation of small bowel pathology. Table 3 Characterisation of mural thickening. Table 5 Site of abnormality in the small bowel. Proximal Distal Adenocarcinoma and coeliac disease Lymphoma and carcinoid tumours, Crohn's disease most commonly affects the terminal ileum with skip lesions elsewhere.

Table 6 Affected layer of the small bowel. Mucosa Submucosa Serosa Crohn's disease, tuberculosis and neoplasms i. Table 4 Symmetry of small bowel thickening. Symmetrical Asymmetrical Benign conditions and some cases of lymphoma Crohn's disease, tuberculosis, adenocarcinomas and gastrointestinal stromal tumours. Extraluminal findings One of the major advantages of CT and other cross-sectional techniques is their ability to visualise the extraluminal soft tissues.

Table 7 Specific indications for CT enterography. The commoner small bowel diseases Crohn's disease CT enterography provides a highly accurate method for diagnosis and assessment of Crohn's disease in adults. Table 8 Primary malignant small bowel tumours. Gastrointestinal bleeding Again, the usual high image quality of CT enterography makes it superior to MRI enterography for the investigation of chronic blood loss.

Comparing CT enterography with other modalities CT enterography has several advantages over small bowel follow-through and conventional enteroclysis [ 1 , 15 ]. Radiation exposure Unlike MR enterography or capsule endoscopy, CT enterography utilises ionising radiation. Multiplanar helical CT enterography in patients with Crohn's disease.

CT enterography as a diagnostic tool in evaluating small bowel disorders: Imaging of small bowel disease: Evaluation of bowel distention and bowel wall appearance by using neutral oral contrast agent for multi-detector row CT. Human Anatomy and Physiology Practice Questions: Self-assessment in Limb X-ray Interpretation. Volume 2 of 2: Now You Don't Have Too! Ultrasound Guidance in Regional Anaesthesia. The Handbook of Ophthalmic Emergencies. Health History and Physical Assessment Vol.

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CT enterography: review of technique and practical tips

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