Hamdan Medical Journal

REVIEW ARTICLE
Year
: 2019  |  Volume : 12  |  Issue : 2  |  Page : 47--51

Updates on the role of imaging in the assessment of crohn's disease


Mohamed Walaaeldin Elfaal 
 Department of Radiology, Thumbay Clinic, Ajman, United Arab Emirates

Correspondence Address:
Mohamed Walaaeldin Elfaal
Department of Radiology, Thumbay Clinic, Ajman
United Arab Emirates

Abstract

As initial studies reported that magnetic resonance imaging (MRI) was useful for the evaluation of the small intestine, this modality has become increasingly important in the diagnosis, assessment and exclusion of small bowel disease. The use of MRI for the assessment of inflammatory bowel disease is increasing, at the expense of the current primary imaging modality and computed tomography (CT) enterography. MRI has many advantages over CT, including a lack of radiation exposure, lower prevalence of adverse events, availability of dynamic information, higher resolution and better soft-tissue contrast. New MRI techniques, including diffusion-weighted imaging, spectroscopy, motility study, positron-emission tomography-MRI and molecular imaging, are currently under investigation to improve the diagnosis, follow-up and management of the disease.



How to cite this article:
Elfaal MW. Updates on the role of imaging in the assessment of crohn's disease.Hamdan Med J 2019;12:47-51


How to cite this URL:
Elfaal MW. Updates on the role of imaging in the assessment of crohn's disease. Hamdan Med J [serial online] 2019 [cited 2020 Dec 1 ];12:47-51
Available from: http://www.hamdanjournal.org/text.asp?2019/12/2/47/236270


Full Text



 Diagnosis



The diagnosis of Crohn's disease (CD) is a clinical one and can be quite difficult, given that the presenting symptoms can be insidious and non-specific.[1] The diagnosis of CD is made on the basis of symptoms and endoscopic and radiological findings.[2]

 Radiological Techniques



Barium small bowel follow-through studies and enteroclysis

The advantage of a small bowel barium study is that it achieves good mucosal detail, and the distension achieved with enteroclysis is reported to improve visualisation of fistulae, sites of small bowel obstruction and mural or intraluminal filling defects such as small bowel neoplasms.[3] Barium studies have a limited role in the diagnosis of acute small-bowel obstruction or ileus and in the assessment of extraluminal disease, and patients are often referred for additional computed tomography (CT) assessment help characterise small bowel lesions or stage small bowel tumours.[3]

Findings

In CD, findings of barium studies include stenosis of the ileocaecal valve, luminal narrowing and ulceration of the terminal ileum, irregular thickening and distortion of the valvulae conniventes, mesenteric and mural thickening causing bowel loop separation and loop adhesions resulting in mass effect.[4]

Severe CD produces a 'cobblestone' appearance, with deep transverse and longitudinal ulcerations bordered by areas of oedema creating a chequered mucosal relief pattern. Chronic CD leads to circumferential thickening of the bowel wall and can progress to fibrotic strictures, in which irreversible deposition of the extracellular matrix causes impaired peristalsis, fixed luminal narrowing and bowel obstruction [Figure 1].[5]{Figure 1}

Ultrasonography

In patients with inflammatory bowel disease (IBD), ultrasonographic findings are non-specific but can be used to guide further studies and to evaluate the effects of treatment. When peroral techniques are used to distend the bowel, the sensitivity and specificity of ultrasonography in the detection of IBD range from 78% to 90% and from 83% to 95%, respectively.[6]

However, ultrasonography is an operator-dependent technique and its use is limited in patients with a large abdomen [Figure 2].[6]{Figure 2}

Computed tomography

CT has proven to have a very high sensitivity (81%–94%) and specificity (96%) for determining the level and cause of high-grade small-bowel obstruction and is now the investigative method of choice for this indication.[3]

The major drawback of CT is patients' exposure to ionising radiation, which has received much attention in recent years given that the IBD population (CD in particular) is likely to require multiple imaging studies over the course of the disease [Figure 3].[8]{Figure 3}

Positron emission tomography/computed tomography: An emergent role in evaluating patients with inflammatory bowel disease

The use of fluorodeoxyglucose (FDG) in positron-emission tomography (PET)/CT is the only modality available that allows both functional and morphological visualisation of the whole gastrointestinal tract, as well as detection of extraintestinal areas of inflammation.[9]

The advantages of PET/CT with FDG include:

Improved spatial localisation compared to PET with FDG without CTReduced FDG uptake in fibrous strictures (indicating failure of medical therapy), compared to non-fibrous areasImproved performance for detecting colon inflammation compared to CT and magnetic resonance (MR) enterography [Figure 4].[3]{Figure 4}

Magnetic resonance imaging

The excellent soft-tissue contrast, direct multiplanar imaging capabilities, new ultrafast breath-holding pulse sequences, lack of ionizing radiation and availability of a variety of oral contrast agents make magnetic resonance imaging (MRI) well suited to a critical role in the imaging of small bowel disorders.[3],[11],[12]

With the increasing awareness of radiation exposure, there has been an increased global interest in implementing techniques that either reduce or eliminate radiation exposure,[12] particularly for patients with CD, who are likely to require multiple imaging studies over the course of their disease.[13]

Two major techniques are used to achieve bowel distension using MRI as follows:

MR enterography with oral contrast administration has been used as the primary MRI modality in CD, with high sensitivity, specificity and interobserver agreement [14]MR enteroclysis, with an infusion of the contrast through a nasojejunal tube, provides superior small bowel distension. The optimal distension of small bowel loops is crucial to evaluate bowel wall pathologies correctly because collapsed bowel loops can hide lesions or mimic disease by suggesting a pathologically thickened bowel wall in collapsed segments, and the visualisation of small polypoid masses that do not produce obstruction is difficult.[3],[11]

MR enteroclysis delineates superficial changes better than MR enterography,[15] and this aspect has to influence the revealing and localising of the disease in patients with only superficial manifestations.

Magnetic resonance imaging sequences

Several different pulse sequences are available for imaging the small bowel. The main diagnostic sequences can be divided into the T2-weighted sequences that consist of the half-Fourier acquisition single-shot turbo spin-echo imaging (HASTE) techniques (single-shot fast spin echo [SSFSE], HASTE and single-shot turbo spin echo) and the balanced gradient echo (fast imaging employing steady-state acquisition, true fast imaging with steady-state precession, balanced fast field echo and balanced steady-state free precession) sequences.[3]

Contrast-enhanced T1-weighted sequences are obtained using a gradient echo technique with fat saturation. The most commonly used sequence in small bowel imaging is fast low-angle shot using both two-dimensional (2D) and three-dimensional (3D) acquisitions. These are routinely used to identify increased enhancement in an inflamed bowel wall [Figure 5].[16]{Figure 5}

T2-weighted sequences are generated by rapid acquisition and relaxation enhancement with ultrafast acquisition time. They are known as half-acquisition SSFSE or SSFSE sequences, depending on the manufacturer. They are heavily T2-weighted sequences, complementary to gadolinium-enhanced gradient echo sequences, and produce a high contrast between the lumen and the bowel wall. As these sequences are highly resistant to magnetic susceptibility or chemical shift artefacts, the wall thickness may be evaluated accurately. Moreover, the sinus tracts and fistulas are well visualised. These sequences are sensitive to intraluminal motion and there may be intraluminal low-intensity signal artefacts.[16]

Balanced steady-state free precession sequences

Balanced steady-state free precession sequences are characterised by two unique features as follows: (1) a very high signal-to-noise ratio and (2) a T2/T1-weighted image contrast.[17]

The recent development of faster pulse sequences provides an opportunity to create a film of cine images.[18] Cine imaging confers the ability to observe the motion of intestinal segments over a relatively short period and in real time. It provides high temporal, spatial and contrast resolution for monitoring bowel contractions.[20]

T1-weighted sequences

After intravenous administration of gadolinium-containing contrast material (0.1–0.2 mmol/kg), dynamic coronal 3D T1-weighted gradient echo sequences with fat suppression are obtained at time intervals of 45–55, 70 and 180 s.[14] These intervals are institutionally specific. Delayed axial and coronal post-contrast 2D or 3D T1-weighted sequences with fat suppression are acquired following dynamic imaging.[19] Although rapid transit to the right colon is seen in some patients, most patients require a delay of at least 40–60 min from contrast material ingestion to imaging.[19]

Diffusion-weighted imaging

Diffusion-weighted imaging (DWI) has long been used in several parts of the body such as the brain. Although the application of DWI to assess the bowel is a relatively new trend, DWI may yield comparable performances for detecting and assessing ileal inflammation in CD.[21] The high signal intensity in DWI and the restricted diffusion of the bowel wall have also has been linked to the detection of acute inflammation [Figure 6].[17]{Figure 6}

 Conclusion



In recent years, several radiological techniques have been developed for the study of the small bowel. Each technique is characterised by its profile of advantages and disadvantages.[22],[23]

A successful approach for the radiologist depends on the local availability of services and clinical expertise. Consideration should always be given to new investigative methods with the utility benefit of reduced radiation exposure, single-study techniques or those with increased diagnostic sensitivity.[3]

In recent years, MR enterography has become a part of standard diagnostic modality in CD. Novel MRI techniques such as DWI, motility studies, PET-MRI and molecular imaging might further contribute to the diagnosis and management of this chronic inflammatory disease.[14]

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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