DustyKat
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The following is an extract from an excellent article that discusses imaging used in Crohn's disease. Aside from the overview below it covers Radiography, Computed Tomography (CT scan), Magnetic Resonance Imaging (MRI), ultrasonography (Ultrasound) and Nuclear Imaging. The full article, with images, can be found here...
http://emedicine.medscape.com/article/367666-overview#a01
Overview
Crohn disease is not a distinct histopathologic entity. Although described and named after its author in 1932, Crohn disease was not clinically, histologically, or radiographically distinguished from ulcerative colitis until 1959.
Currently, the diagnosis of Crohn disease entails an analysis of clinical, radiologic, endoscopic, pathologic, and stool specimen results. Contrast-enhanced radiography is used to localize the extent, severity, and contiguity of disease; CT scanning provides cross-sectional images for assessing mural and extramural involvement; endoscopy enables direct visualization of the mucosa and provides the ability to obtain a biopsy specimen for histopathologic correlation; and ultrasonography and MRI are adjuncts that provide alternative cross-sectional images in populations in whom radiation exposure is a concern.
Preferred Examination
The preferred examinations are plain radiography, double-contrast barium enema examination, single-contrast upper GI series with small-bowel follow-though or enteroclysis with CT, and double-contrast evaluation of the small bowel. Ultrasonography and MRI can be used as adjuncts if radiation exposure is an issue in monitoring disease activity.
In general, the clinician should select CT first in evaluation of Crohn disease. CT has is not as sensitive in delineating fissure or fistula as barium studies, but it is superior to barium studies in showing the extraluminal sequelae of Crohn disease. Residual contrast material from barium studies leads to severe streak artifact on CT scans due to hyperattenuating contrast suspension used in barium studies. On the other hand, CT contrast residue does not preclude a barium study.
Barium contrast studies are limited in the evaluation of transluminal inflammation in Crohn disease; distention of small bowel with contrast material is required for proper evaluation. Slow passage of the contrast agent through the pylorus can result in nonvisualization of small-bowel lesions in small bowel series. Enteroclysis is one way to circumvent the dilemma by passing a catheter to the duodenal jejunal junction.
Abdominal radiographic findings are not specific for Crohn disease. Radiography is useful in evaluation of bowel-loop distention and pneumoperitoneum. Sonographic findings have high variability because of operator dependence in detection of the bowel-wall changes seen in Crohn disease. Transmission of ultrasound waves through fatty tissues is limited, and detection may be severely limited by the patient's body habitus.
Traditionally, MRI was limited to the evaluation of the abdomen because of motion artifact. With stronger gradients, breath-hold imaging is possible, and MRI of the abdomen and pelvis can be readily performed in most patients. In addition, optimal imaging with MRI often requires the use of large volumes of positive or negative contrast agents given either orally or via a nasojejunal or rectal tube. However, acutely ill patients may not be able to tolerate a large oral fluid load. If suboptimal distention occurs, detection of inflamed segments of bowel may be limited. Air in the colon can be a substantial susceptibility artifact with some sequences, especially gradient-echo sequences.
CT-Guided Therapy
CT has become the procedure of choice not only in diagnosing Crohn disease but also in managing abscesses. A growing body of literature shows that CT-guided percutaneous abscess drainage may obviate surgery. In studies, CT percutaneous abscess drainage has shown great success either as a temporizing measure or as definitive therapy with a decreased rate of recurrence, as compared with that of surgery. Because about 70-90% of patients with regional enteritis eventually require surgery, avoiding an operation to treat an abscess is a tangible benefit of CT.
Complications and Contraindications
The oral administration of contrast material is to be avoided when moderate- or high-grade colonic obstruction is present. Double-contrast (air contrast) barium enema examination is contraindicated in patients with severe colitis, because injection of air with contrast agent may precipitate toxic megacolon or colonic perforation. Barium studies are contraindicated when there are signs and symptoms of peritonitis or when there are radiographic signs of gas in the bowel wall or pneumoperitoneum.
The intravenous injection of contrast material for CT studies should be avoided when chronic renal insufficiency is present, when there is continued use of Glucophage, or when there are signs and symptoms of acute renal failure. CT and barium studies use ionizing radiation, which may result in considerable radiation burden. This exposure is a relative contraindication in pregnancy and childhood. Sonography and MRI may prove to be useful alternative imaging modalities.
http://emedicine.medscape.com/article/367666-overview#a01
Overview
Crohn disease is not a distinct histopathologic entity. Although described and named after its author in 1932, Crohn disease was not clinically, histologically, or radiographically distinguished from ulcerative colitis until 1959.
Currently, the diagnosis of Crohn disease entails an analysis of clinical, radiologic, endoscopic, pathologic, and stool specimen results. Contrast-enhanced radiography is used to localize the extent, severity, and contiguity of disease; CT scanning provides cross-sectional images for assessing mural and extramural involvement; endoscopy enables direct visualization of the mucosa and provides the ability to obtain a biopsy specimen for histopathologic correlation; and ultrasonography and MRI are adjuncts that provide alternative cross-sectional images in populations in whom radiation exposure is a concern.
Preferred Examination
The preferred examinations are plain radiography, double-contrast barium enema examination, single-contrast upper GI series with small-bowel follow-though or enteroclysis with CT, and double-contrast evaluation of the small bowel. Ultrasonography and MRI can be used as adjuncts if radiation exposure is an issue in monitoring disease activity.
In general, the clinician should select CT first in evaluation of Crohn disease. CT has is not as sensitive in delineating fissure or fistula as barium studies, but it is superior to barium studies in showing the extraluminal sequelae of Crohn disease. Residual contrast material from barium studies leads to severe streak artifact on CT scans due to hyperattenuating contrast suspension used in barium studies. On the other hand, CT contrast residue does not preclude a barium study.
Barium contrast studies are limited in the evaluation of transluminal inflammation in Crohn disease; distention of small bowel with contrast material is required for proper evaluation. Slow passage of the contrast agent through the pylorus can result in nonvisualization of small-bowel lesions in small bowel series. Enteroclysis is one way to circumvent the dilemma by passing a catheter to the duodenal jejunal junction.
Abdominal radiographic findings are not specific for Crohn disease. Radiography is useful in evaluation of bowel-loop distention and pneumoperitoneum. Sonographic findings have high variability because of operator dependence in detection of the bowel-wall changes seen in Crohn disease. Transmission of ultrasound waves through fatty tissues is limited, and detection may be severely limited by the patient's body habitus.
Traditionally, MRI was limited to the evaluation of the abdomen because of motion artifact. With stronger gradients, breath-hold imaging is possible, and MRI of the abdomen and pelvis can be readily performed in most patients. In addition, optimal imaging with MRI often requires the use of large volumes of positive or negative contrast agents given either orally or via a nasojejunal or rectal tube. However, acutely ill patients may not be able to tolerate a large oral fluid load. If suboptimal distention occurs, detection of inflamed segments of bowel may be limited. Air in the colon can be a substantial susceptibility artifact with some sequences, especially gradient-echo sequences.
CT-Guided Therapy
CT has become the procedure of choice not only in diagnosing Crohn disease but also in managing abscesses. A growing body of literature shows that CT-guided percutaneous abscess drainage may obviate surgery. In studies, CT percutaneous abscess drainage has shown great success either as a temporizing measure or as definitive therapy with a decreased rate of recurrence, as compared with that of surgery. Because about 70-90% of patients with regional enteritis eventually require surgery, avoiding an operation to treat an abscess is a tangible benefit of CT.
Complications and Contraindications
The oral administration of contrast material is to be avoided when moderate- or high-grade colonic obstruction is present. Double-contrast (air contrast) barium enema examination is contraindicated in patients with severe colitis, because injection of air with contrast agent may precipitate toxic megacolon or colonic perforation. Barium studies are contraindicated when there are signs and symptoms of peritonitis or when there are radiographic signs of gas in the bowel wall or pneumoperitoneum.
The intravenous injection of contrast material for CT studies should be avoided when chronic renal insufficiency is present, when there is continued use of Glucophage, or when there are signs and symptoms of acute renal failure. CT and barium studies use ionizing radiation, which may result in considerable radiation burden. This exposure is a relative contraindication in pregnancy and childhood. Sonography and MRI may prove to be useful alternative imaging modalities.
