Small Bowel Enema

The small bowel enema (enteroclysis) is a fluoroscopic study in which a tube is passed through the nose and stomach into the duodenojejunal flexure under fluoroscopy, and a continuous infusion of barium sulphate followed by methylcellulose (a double contrast technique) or water is delivered at a controlled rate of 80 to 120 mL each minute.

The controlled infusion distends the whole small bowel, overcomes the normal variation of peristalsis, and shows the folds, wall and loops of the jejunum and ileum in far more detail than a follow through. Fluoroscopic spot films and compression films of the pelvic ileum are taken as the contrast advances. The study takes 30 to 60 minutes.

The effective dose is about 6 to 10 mSv, more than most other contrast studies, because of the long fluoroscopy time.

Small bowel disease is often missed because the bowel is long, mobile and out of reach of the endoscope. CT enterography and MR enterography have replaced the enema in most centres, since they show the wall, mesentery, nodes and extramural disease without a tube, and MR gives no ionising radiation.

The enema is still used where cross-sectional enterography is not available, and for selected problems: suspected low grade or intermittent adhesive obstruction, subtle strictures, and suspected small bowel tumour with negative cross-sectional imaging.

Indications. Recurrent or intermittent subacute small bowel obstruction with unclear cause. Suspected adhesions, strictures or internal hernia. Crohn disease when MR or CT enterography is unavailable. Obscure gastrointestinal bleeding or iron deficiency anaemia with negative endoscopy and unavailable enterography.

Suspected small bowel tumour (lymphoma, carcinoid, adenocarcinoma, stromal tumour). Unexplained chronic abdominal pain, weight loss or diarrhoea. Suspected radiation enteritis. Suspected Meckel diverticulum or other diverticula. Not for acute obstruction with pain, vomiting and distension, and not for routine investigation of functional symptoms.

Contraindications and precautions. Suspected perforation or leak (use water soluble contrast, or avoid the study). Complete obstruction where barium may impact. Severe cardiopulmonary disease or poor co-operation (nasal intubation is unpleasant). Pregnancy: avoid.

Smooth muscle relaxants are avoided in glaucoma, prostatic obstruction and tachyarrhythmias (hyoscine butylbromide), and in phaeochromocytoma and insulinoma (glucagon). Recent bowel surgery with a possible anastomotic leak. Allergy to latex or local anaesthetic spray.

Preparation and technique. Fasting for 6 to 8 hours, light diet the day before, and bowel preparation with a mild laxative if required by local practice.

The throat is anaesthetised with spray, the tube is passed under fluoroscopy to the duodenojejunal flexure, and the barium is infused with the patient in the supine position, followed by methylcellulose or water, and spot films every few minutes. Compression of the pelvic loops with a paddle separates overlapping loops. Patients drink fluids afterwards to clear the barium.

Normal appearances. The jejunum has a feathery pattern of thin, regular valvulae conniventes (2 to 3 mm thick, 3 to 4 folds in each 2.5 cm), a diameter up to 3 cm, and a calibre that narrows smoothly towards the ileum. The ileum has fewer, thinner folds, a diameter up to 2.5 cm, and a smooth outline.

The terminal ileum enters the caecum through the ileocaecal valve with a smooth, tapered lumen. Loops are separated by 1 to 2 mm of bowel wall in normal people, and the mucosal outline remains smooth with the contrast. Peristalsis moves the contrast steadily to the caecum within 1 to 2 hours during a controlled infusion.

Interpretation.

• Strictures: a fixed narrowing with dilated bowel proximal to it, a transition point, and a smooth taper (adhesions, post-inflammatory) or a shouldered irregular edge (tumour). Adhesive bands cause angulation and kinking of loops, with fixation of loops that do not move on compression.
• Crohn disease: thickened, nodular folds, cobblestone mucosa, deep longitudinal and transverse ulcers, the "string sign" (a long narrow terminal ileal lumen), skip lesions, sacculations on the antimesenteric border, separation of loops by mesenteric fat and thickening, fistulae (enteroenteric, enterovesical, enterocutaneous) and sinus tracts.
• Tuberculosis: ileocaecal disease with a contracted, conical caecum, a gaping ileocaecal valve and a stenosed terminal ileum, with multiple short strictures.
• Tumours: a polypoid filling defect, an annular "apple core" constriction, or an ulcerated mass (adenocarcinoma, usually in the duodenum or jejunum), lymphoma (bulky wall thickening with aneurysmal dilatation, or multiple nodules), carcinoid (a submucosal mass, fixed kinked loops from a desmoplastic reaction), and stromal tumours (an exophytic mass with ulcer). Intussusception shows a coiled spring pattern with a lead mass.
• Coeliac disease and malabsorption: dilated loops, a loss of the jejunal fold pattern with an ileal fold pattern in the jejunum, "jejunisation of the ileum", flocculation and segmentation of contrast, and transient intussusception; scleroderma shows closely packed, wire spring ("hide bound") folds.
• Radiation enteritis: fixed, thickened, narrowed loops in the pelvis, with straightened folds and adhesions.
• Diverticula: jejunal diverticulosis, with contrast filled outpouchings on the mesenteric border and stasis; Meckel diverticulum, a blind pouch on the antimesenteric side of the ileum.
• Vascular: angiodysplasia is rarely shown; mesenteric ischaemia causes thumbprinting and thickened folds.
• Lymphoid hyperplasia: multiple small 1 to 3 mm nodules, especially in the terminal ileum (normal in children, and in immunoglobulin deficiency).
• Parasites: ascariasis shows a linear filling defect of the worm, which may take up contrast in its gut.
• Post-operative: anastomotic stricture, afferent loop syndrome, and a leak with extraluminal contrast.

Critical values and findings needing immediate action.

• Extravasation of contrast (perforation): stop the study, surgical review, antibiotics and resuscitation.
• High grade or complete obstruction with failure of contrast to progress and pain or vomiting: nasogastric decompression, intravenous fluids and surgical review.
• Closed loop obstruction or ischaemic signs (a persistent fixed loop, severe pain, fever, raised lactate): emergency surgery.
• Mass lesion or a malignant stricture: urgent cross-sectional staging, biopsy and multidisciplinary referral.
• Aspiration of barium during intubation: suction, oxygen, and a chest film.
• Severe Crohn stricture with fistula and sepsis: antibiotics, imaging for abscess and specialist referral.

Limitations and artefacts.

• The study shows only the lumen and mucosal outline, not the bowel wall, mesentery, nodes or extraintestinal disease; CT or MR enterography is needed for these.
• Intubation is uncomfortable and carries a risk of aspiration, perforation (rare, under 1 in 10 000) and vasovagal reactions; it is unsuitable for frail and uncooperative patients.
• Overlapping pelvic loops, rapid transit, poor distension and flocculation of barium mimic disease; pseudo strictures arise from peristalsis, so a narrowing must persist on several films and with compression.
• An underfilled loop or a spastic segment mimics a stricture, and a segment with dilution of barium hides mucosal detail.
• Dose is higher than for other contrast studies, so repeated studies are avoided, and MR or ultrasound is preferred in young patients with inflammatory bowel disease.
• Residual barium obscures later CT and may impact proximal to a stricture.
• Findings are non-specific: biopsy and endoscopic or surgical correlation are needed to name the cause of a stricture or mass.

Special groups.

• Children: avoid; use MR enterography, ultrasound or a follow through.
• Young patients with Crohn disease: MR enterography, small bowel ultrasound and faecal calprotectin avoid cumulative dose.
• Patients with previous abdominal surgery: adhesive obstruction is the commonest indication.
• Immunocompromised patients: lymphoid hyperplasia, infection and lymphoma.
• Pregnancy: avoid.
• Regions: small bowel tuberculosis, typhoid, ascariasis, hookworm, and lymphoma (including immunoproliferative small intestinal disease) are seen in endemic areas, and the enema or follow through may be the only small bowel imaging available.

Follow up tests. MR or CT enterography, capsule endoscopy (after exclusion of stricture, with a patency capsule if needed), balloon assisted enteroscopy with biopsy, colonoscopy with ileoscopy, faecal calprotectin, coeliac serology, tissue transglutaminase antibody, full blood count, iron studies, albumin, C-reactive protein, stool microscopy for parasites, tuberculosis tests, HIV test, and referral to gastroenterology, surgery or oncology.