Crohn's Disease

Preliminary Diagnosis: Crohn's Disease

I. What imaging technique is first-line for this diagnosis?

• CT of the abdomen and pelvis with IV and oral contrast is indicated in patients with abdominal pain in whom enteritis/colitis is suspected, or to evaluate for complications of known Crohn's disease (e.g., abscess, stricture, obstruction).

• Endoscopy with tissue biopsy is the gold standard for diagnosis of Crohn's disease (CD).

II. Describe the advantages and disadvantages of this technique for diagnosing Crohn's disease.

Advantages

• Can show the features associated with Crohn's disease, such as bowel wall thickening, fatty proliferation, abscesses, strictures/fistulas, small bowel obstruction, perforation, free fluid, mesenteric fat stranding, and lymphadenopathy, which may guide further workup with endoscopy and tissue biopsy.

• Relatively quick imaging procedure.

• Requires minimal patient cooperation and is less susceptible to motion artifact.

• Extraintestinal manifestations, including gallstones, spondyloarthropathies, pancreatitis and renal stones also may be detected.

Disadvantages

• Not diagnostic for Crohn's disease.

• Exposure to ionizing radiation.

• Potential for renal injury from intravenous contrast agents; assessment of renal function is required prior to administration of IV contrast.

III. What are the contraindications for the first-line imaging technique?

• Patients with allergic reactions (e.g. itching, rash) to intravenous contrast and more severe allergic reactions (e.g.angioedema) should be pretreated with steroids and antihistamines for a minimum of 13 hours prior to CT imaging with IV contrast. Anaphylaxis to prior contrast administration is an absolute contraindication to intravenous contrast.

• Relatively contraindicated in pregnant women, especially within the first two trimesters. In certain institutions, informed consent is required prior to imaging pregnant women with CT.

IV. What alternative imaging techniques are available?

• Contrast enhanced magnetic resonance enterography.

• Acute abdominal series x-rays.

• Upper gastrointestinal barium studies with small bowel follow through, as well as barium enemas.

• Ultrasound.

• Dual x-ray absorptiometry (DEXA).

• Magnetic resonance cholangiopancreatography (MRCP).

V. Describe the advantages and disadvantages of the alternative techniques for diagnosing Crohn's disease.

Contrast enhanced magnetic resonance enterography

Advantages

• Has been shown to be an accurate method of monitoring the activity of CD and evaluating therapeutic effectiveness and visualization of fistulas.

• Sensitive in detecting fistulas, sinuses, abscesses and perianal involvement (a difficult location to visualize on CT).

Disadvantages

• Expensive.

• Requires significant patient cooperation to minimize artifact.

• Abundance of bowel gas limits resolution.

Acute abdominal series x-ray

Advantages

• Can provide information quickly regarding bowel dilation, obstruction and possible free air.

• Inexpensive.

Disadvantages

• Not diagnostic for Crohn's disease.

• Often findings are very nonspecific.

Upper gastrointestinal barium studies with small bowel follow through, as well as barium enemas

Advantages

• Can help visualize mucosal irregularities and the extent of stricture, assess for obstruction and aid in the detection of fistulas.

Disadvantages

• Not diagnostic for Crohn's disease.

• Exposure to ionizing radiation.

Magnetic resonance cholangiopancreatography (MRCP)

Advantages

• Can evaluate for strictures/beading of the biliary tree seen in primary sclerosing cholangitis; endoscopic retrograde cholangiopancreatography can then be performed for confirmation of the disease.

Disadvantages

• Expensive.

• Requires significant patient cooperation to minimize artifact motion.

VI. What are the contraindications for the alternative imaging techniques?

Contrast enhanced magnetic resonance enterography and MRCP

• Contraindications include metallic foreign bodies.

• Claustrophobia and pregnancy are relative contraindications.

• Renal failure is an absolute contraindication to gadolinium based contrast if the glomerular filtration rate is less than 30. Contrast is also an absolute contraindication in pregnancy. Pretreatment with steroids and antihistamines is required in patients with history of allergy to gadolinium-based contrast agents.

Acute abdominal series x-ray

No contraindications to plain radiographs exist.

Upper gastrointestinal barium studies with small bowel follow through, as well as barium enemas

Contraindications include patients with high aspiration risk and bowel perforation. Water soluble contrast agents, such as Omnipaque, can be used in these patients with caution. Additional contraindications include patients with peritoneal signs due to high risk of causing a perforation.

Ultrasound

No contraindications to ultrasound exist.

DEXA

No contraindications to DEXA exist.