CT Enterography
CT enterography (CTE) is a multiphase contrast enhanced CT of the abdomen and pelvis with oral neutral contrast (1.0 to 1.5 litres of 0.1% barium sulphate suspension, water, or a mannitol or polyethylene glycol solution taken over 45 to 60 minutes) to distend the small bowel and intravenous contrast (100 to 120 mL of non-ionic medium at 3 to 4 mL each second) to show mural enhancement.
The enteric phase is acquired at 45 to 55 seconds after injection (the small bowel mucosa enhances maximally), usually followed by a portal venous phase at 70 seconds. Thin slices (0.6 to 1.25 mm) are reconstructed in axial, coronal and sagittal planes with curved planar views.
Anti-peristaltic drugs (hyoscine butylbromide 20 mg or glucagon) improve distension where tolerated. Effective dose is about 8 to 15 mSv. CT enteroclysis (nasojejunal tube infusion of contrast) gives better distension but is less used.
CTE shows the bowel wall and the extramural structures in a single examination, with a sensitivity of 85 to 95% and a specificity of 90 to 95% for active small bowel Crohn disease, and about 85 to 95% sensitivity for small bowel tumours and obscure gastrointestinal bleeding sources.
Crohn disease affects 100 to 300 in 100 000 people in high incidence regions, with the terminal ileum involved in about 50 to 70%. The small bowel represents about 75% of the gut's length but only 2 to 3% of gastrointestinal tumours, which are often diagnosed late.
Indications. Known or suspected Crohn disease: diagnosis, extent, activity, complications (stricture, fistula, abscess), and distinguishing inflammatory from fibrotic strictures. Obscure gastrointestinal bleeding after negative upper endoscopy and colonoscopy. Suspected small bowel tumours (neuroendocrine tumour, adenocarcinoma, lymphoma, gastrointestinal stromal tumour, metastasis).
Small bowel obstruction of uncertain cause, incomplete obstruction, and recurrent subacute obstruction. Malabsorption and coeliac disease complications (lymphoma, ulcerative jejunitis). Polyposis syndromes (Peutz-Jeghers).
Tuberculosis of the intestine, radiation enteritis, and ischaemic strictures. Post-operative assessment of Crohn disease recurrence and anastomosis. Not for acute abdominal pain with suspected perforation or complete obstruction (routine CT is used), and not for a first look at young patients with Crohn disease, where MR enterography and bowel ultrasound avoid radiation.
Contraindications and precautions. Previous severe contrast reaction, renal impairment (estimated glomerular filtration rate under 30 mL each minute: weigh carefully), pregnancy, suspected perforation or high grade obstruction (oral contrast is not given; haemodynamic instability), and aspiration risk. Metformin (follow local advice).
Hyoscine is avoided in glaucoma, prostate enlargement with retention, and tachyarrhythmia; glucagon is avoided in phaeochromocytoma and insulinoma.
Oral contrast may cause diarrhoea (mannitol and polyethylene glycol). Repeated studies in young patients with Crohn disease accumulate a large radiation dose, so MR enterography or ultrasound is preferred for follow up.
Preparation and technique. Fasting for 4 to 6 hours. The patient drinks the neutral oral contrast (900 to 1500 mL) in divided portions over 45 to 60 minutes, finishing about 10 to 15 minutes before the scan. A cannula of 18 to 20 G is placed.
Hyoscine or glucagon is given just before scanning to reduce peristalsis. The patient lies supine with arms raised over the head. Intravenous contrast is injected with a pump, and the enteric phase at 45 to 55 seconds, with a portal phase at 70 seconds in selected cases.
Coronal reformats follow the bowel loops. Dual energy or low dose techniques lower the exposure. The report names the segment involved, the length of disease, the wall thickness, the enhancement pattern and complications.
