Barium Enema

The barium enema is a fluoroscopic examination of the colon and rectum after barium sulphate and air are introduced through a rectal tube, with spot films and overhead films in multiple positions. The double contrast barium enema coats the mucosa with a thin layer of high density barium and distends the colon with air, which shows polyps, small ulcers and mucosal patterns in fine detail.

A single contrast enema (thin barium or water soluble contrast) shows the outline and calibre of the bowel, with less mucosal detail, and is used for sick, frail or obstructed patients, for suspected volvulus or fistula, and for post-operative leaks. Therapeutic enemas (air or contrast enema reduction of intussusception in children) are covered by the same technique.

The effective dose is about 5 to 8 mSv, similar to 2 to 3 years of natural background radiation.

Colonoscopy and CT colonography have replaced the double contrast barium enema for most indications, because they have higher sensitivity for polyps and cancer (colonoscopy 95 to 98% for polyps over 1 cm, and CT colonography 85 to 95%, against 70 to 85% for double contrast barium enema), and they give a tissue diagnosis (colonoscopy) or extracolonic information (CT).

The barium enema is used where these tests are unavailable, when colonoscopy is incomplete or unsafe (strictures, tortuous colon, anticoagulation), and for specific functional and paediatric indications.

Indications. Change in bowel habit, rectal bleeding, anaemia or abdominal pain where colonoscopy or CT colonography is not available, or after an incomplete colonoscopy. Diverticular disease and stricture assessment. Suspected sigmoid or caecal volvulus (water soluble single contrast enema). Suspected large bowel obstruction (water soluble contrast to show the level and cause).

Colonic fistula or sinus tracts and anastomotic leak after surgery (water soluble contrast). Intussusception in children (contrast or air enema for diagnosis and reduction). Hirschsprung disease (to show the transition zone before biopsy) and neonatal low obstruction (meconium ileus, atresia, small left colon). Chronic constipation with suspected megacolon.

Inflammatory bowel disease extent, when other methods are not available. Not for acute severe colitis, or for screening of asymptomatic people.

Contraindications and precautions. Toxic megacolon and acute severe colitis (risk of perforation). Suspected perforation (use water soluble contrast and caution). Recent deep rectal or colonic biopsy or polypectomy (within about 1 week for barium, because of the risk of perforation). Complete obstruction, where barium may impact (water soluble contrast is used).

Smooth muscle relaxant (hyoscine butylbromide or glucagon) is avoided in glaucoma, prostatic obstruction and severe cardiac disease (hyoscine) or phaeochromocytoma and insulinoma (glucagon). Latex allergy: use latex free balloon catheters. Pregnancy: avoid. Frail patients may not tolerate bowel preparation or positioning.

Preparation and technique. The colon must be clean: a low residue diet for 2 to 3 days, plenty of fluids, a stimulant and osmotic laxative the day before (and none in suspected obstruction or severe colitis), and nothing to eat for 4 to 6 hours.

The tube is inserted into the rectum, barium is run in under fluoroscopy to the caecum or the splenic flexure, the barium is drained, air is insufflated, and films are taken with the patient turned and tilted to show every segment. The study takes 20 to 40 minutes, and patients are told to drink fluids and take laxatives afterwards to prevent barium retention.

Normal appearances. A uniform haustral pattern from the caecum to the transverse colon, a smooth and thin contrast line on the mucosa in double contrast films, with fine mucosal areae lines (innominate lines) and no filling defects, a calibre of under 6 cm (caecum under 9 cm), a regular rectum with the valves of Houston, and a smooth sigmoid loop.

The ileocaecal valve is seen as a lip on the medial wall of the caecum and may show reflux into the terminal ileum. The appendix may fill with barium in some people, which is normal.

Interpretation.

• Diverticular disease: multiple small outpouchings, mostly in the sigmoid, with a "saw tooth" outline from muscular thickening of the wall, narrowing and shortening of the segment, and complications (diverticulitis shows spasm and a pericolic collection, and a fistula to the bladder or vagina is possible).
• Colorectal polyps: round or oval filling defects or ring shadows with a stalk or a broad base ("Mexican hat" sign), with sensitivity for polyps over 1 cm of about 70 to 85%. Polyps over 1 cm are removed at colonoscopy.
• Carcinoma: an annular constricting lesion with shouldered edges ("apple core"), a fixed, irregular mass or an ulcerating plaque, with an abrupt transition; any suspected cancer is confirmed by colonoscopy with biopsy and staged by CT.
• Ulcerative colitis: loss of haustral markings, a granular mucosal surface, "collar button" ulcers, a shortened, narrow colon with a "lead pipe" appearance in chronic disease, backwash ileitis, and pseudopolyps; contrast enema is avoided in acute severe disease.
• Crohn colitis: asymmetric disease with skip lesions, aphthous ulcers, linear and "rose thorn" ulcers, cobblestone mucosa, strictures and fistulae, with the rectum often spared.
• Ischaemic colitis: thumbprinting from submucosal oedema and haemorrhage at the splenic flexure and descending colon, with a stricture in the healing phase.
• Infective colitis: tuberculosis (cone shaped, contracted caecum with the ileocaecal valve patulous or gaping), amoebiasis (caecal and rectosigmoid ulceration and an amoeboma, a mass like narrowing), and schistosomiasis (polyposis of the rectum and sigmoid, and mural calcification).
• Volvulus: sigmoid volvulus shows a "bird's beak" tapering at the point of twist on a contrast enema, and caecal volvulus shows a bird's beak at the caecum with a dilated, displaced loop.
• Intussusception: a "coiled spring" or a filling defect with a "claw" sign as contrast outlines the apex of the intussusceptum; the study is followed by reduction by hydrostatic or pneumatic pressure.
• Hirschsprung disease: a narrow aganglionic rectosigmoid segment, a cone shaped transition zone, a dilated proximal colon, an inverted rectosigmoid ratio (rectum narrower than sigmoid), irregular contractions, and delayed barium evacuation at 24 hours.
• Neonatal conditions: microcolon (meconium ileus, ileal atresia, total colonic aganglionosis), small left colon syndrome (maternal diabetes), and meconium plug.
• Megacolon: chronic dilatation with faecal loading, with a normal or dilated rectum (idiopathic or Chagas disease, Hirschsprung disease).
• Fistulae and sinuses: contrast tracking to the bladder, vagina, skin or adjacent bowel in diverticulitis, Crohn disease and malignancy.
• Post-operative: anastomotic stricture or leak (contrast outside the lumen), a stoma study, and rectal stump assessment before reversal.
• Extrinsic compression: smooth indentation by masses, endometriosis, adhesions and enlarged organs.

Critical values and findings needing immediate action.

• Contrast extravasation or perforation (barium in the peritoneum): urgent surgical review, broad spectrum antibiotics, resuscitation and operation or peritoneal lavage, since barium peritonitis has a high mortality.
• Large bowel obstruction with a suspected carcinoma or volvulus: surgical referral, with decompression of sigmoid volvulus by flexible sigmoidoscopy.
• Intussusception: if reduction by enema succeeds, observe the child; if there are signs of peritonitis or perforation, proceed to surgery.
• Toxic megacolon seen on the preliminary film: stop the study, treat the colitis and involve the surgeon.
• Findings of carcinoma: urgent colonoscopy and biopsy, staging CT and multidisciplinary referral.
• Hirschsprung disease with enterocolitis (fever, distension, explosive diarrhoea): resuscitation, rectal washout and surgical review.
• Barium impaction or severe pain after the examination: urgent assessment for perforation or obstruction.

Limitations and artefacts.

• Sensitivity for polyps and early cancer is lower than colonoscopy and CT colonography, especially for polyps under 1 cm, in the sigmoid colon (diverticular disease, overlapping loops), in the rectum and caecum; false negative rates for cancer of 5 to 10% are reported.
• Residual faeces, bubbles, poor coating and spasm mimic or hide polyps, and a filling defect that moves with position is faeces; the colon should be re-examined after cleansing or with colonoscopy when doubt persists.
• The study cannot provide a tissue diagnosis, and any abnormality requires colonoscopy or biopsy.
• Rectal tube and balloon inflation can cause perforation (about 1 in 25 000 for barium enema, with higher rates in patients with colitis and rectal biopsy and when the balloon is inflated in the rectum), vasovagal reactions, and cardiac arrhythmia; the balloon should be avoided in rectal disease and in patients with an anal stricture.
• Barium can be retained and cause constipation, impaction, or appendicitis (if the barium enters the appendix and is retained), and patients must be given laxatives and fluids.
• Hyoscine causes blurred vision and tachycardia, and glucagon causes nausea and hypoglycaemia in fasting patients.
• Dose is higher than most plain radiography and cumulative for patients with inflammatory bowel disease; use MR or ultrasound when possible.
• Extracolonic disease (liver metastases, nodes, pelvic masses) is not shown, and staging needs CT.
• Barium in the colon interferes with subsequent CT and colonoscopy for several days to weeks.

Special groups.

• Children: contrast enema for intussusception (with air or water soluble contrast under controlled pressure), Hirschsprung disease and neonatal obstruction, with a paediatric surgeon available.
• Older and frail adults: single contrast water soluble enema when preparation and positioning are difficult, often for suspected obstruction or volvulus.
• Patients with colitis: avoid the study in acute severe disease and avoid bowel preparation with stimulant laxatives; MR or colonoscopy for assessment of extent and complications.
• Patients with stomas: contrast studies of the efferent and afferent limbs with a Foley catheter.
• Pregnancy: avoid.
• Regions: sigmoid volvulus and intussusception are frequent surgical emergencies in many regions, schistosomal and amoebic colitis, colonic tuberculosis and Chagas megacolon (in Latin America) appear on contrast studies, and a single contrast enema is often the only available colonic imaging.

Follow up tests. Colonoscopy with biopsy and polypectomy, CT colonography, CT abdomen and pelvis for staging and extracolonic disease, flexible sigmoidoscopy for volvulus decompression and distal lesions, anorectal manometry and rectal suction biopsy for Hirschsprung disease, faecal calprotectin, stool microscopy and culture, serology for schistosomiasis and amoebiasis,

carcinoembryonic antigen, full blood count and iron studies, ultrasound for intussusception, and referral to gastroenterology, colorectal surgery or oncology.