barium enema

**Procedure:** Barium sulfate suspension is introduced through a rectal tube, often with air insufflation (double-contrast/air-contrast) to coat the mucosa and distend the lumen. Fluoroscopic spot films are then taken. Bowel prep is generally required. It has largely been replaced by colonoscopy and CT colonography for screening and diagnosis, but it is still used for specific indications in pediatrics and for functional or anatomic questions.

**High-yield findings:** - **Colorectal carcinoma:** "Apple core" lesion, a circumferential annular constricting mass with shouldered margins, most often in the left colon. - **Ulcerative colitis (chronic):** "Lead pipe" colon, from loss of haustra and a shortened, rigid, tubular colon. Also "collar-button" ulcers and pseudopolyps. Disease is continuous, starts in the rectum, and is limited to the mucosa and submucosa. - **Crohn disease:** "String sign" (terminal ileum stricture), skip lesions, cobblestoning, and fistulae. This is usually seen on small-bowel follow-through, but it can be seen on enema when the terminal ileum is refluxed. - **Sigmoid volvulus:** "Bird's beak" at the twisted point, with a "coffee bean" sign on plain film. Barium enema can sometimes reduce it, but endoscopic decompression is preferred. - **Intussusception (pediatric):** "Coiled spring" appearance, and the enema can be therapeutic. Air or contrast enema reduction is used in stable children. It is contraindicated with peritonitis or perforation. - **Hirschsprung disease:** A narrow, aganglionic distal segment with a transition zone and a dilated proximal colon. Definitive diagnosis requires a rectal suction biopsy showing absent ganglion cells and hypertrophied nerve trunks with ↑ acetylcholinesterase staining. - **Diverticulosis:** Outpouchings, with a "saw-tooth" appearance in the sigmoid colon from muscular hypertrophy. - **Malrotation and Ladd bands:** The cecum is abnormally positioned. Midgut volvulus is better evaluated with an upper GI series ("corkscrew" duodenum). - **Colonic polyps:** Filling defects, "Mexican hat" sign for pedunculated or sessile polyps seen en face.

**Contraindications:** - Suspected perforation, toxic megacolon, or fulminant colitis. Barium leaking into the peritoneum causes severe peritonitis and adhesions, so use water-soluble contrast if perforation is a concern. - Recent deep rectal biopsy or polypectomy, because of perforation risk. - Peritoneal signs.

**Complications:** Perforation (rare), barium impaction or constipation, barium peritonitis, vasovagal reactions, and aspiration (rare). Barium retained in the colon can also obscure later studies, so barium studies should be done after CT or endoscopy when both are planned.

**Test-taking pearls:** - Barium swallow is used for esophageal pathology (e.g., achalasia "bird's beak," esophageal webs, Zenker diverticulum). Barium enema is for the colon. - Gastrografin (water-soluble) is preferred if perforation or leak is suspected, but it is hyperosmolar and risky if aspirated, because it can cause pulmonary edema. - Colonoscopy is the preferred test when biopsy or therapeutic intervention is needed.