Ch07: GI Imaging — Barium Studies（消化道造影）

# Ch07: GI Imaging — Barium Studies（消化道造影）

Preparatory Mindset

GI imaging uses plain film, barium studies (barium sulfate), water-soluble contrast, CT, MRI and angiography. The barium study is the classic teaching tool: barium sulfate gives excellent opacification and good mucosal coating and is completely inert — but it solidifies and impacts proximal to a stricture and causes severe inflammatory peritonitis if it leaks. Water-soluble contrast is used when perforation or anastomotic leak is suspected (it does not cause inflammatory peritonitis). The exam focuses on: basic signs of barium study (ulcer vs filling defect) and differentiating benign from malignant ulcer.

Core Concepts

Imaging modalities for GI

• Plain film: free air (upright), gas/fluid levels in dilated loops, calcifications.
• Barium study: single or double contrast; double contrast gives better mucosal visualization (air pushes barium against the mucosa). Views: mucosal relief, single contrast, double contrast.
• CT: shows full width of GI wall and surrounding fat; staging of GI malignancy, intra-abdominal masses; virtual colonoscopy; adequate distention is key.
• MRI: limited by peristalsis artifacts; excellent for rectal carcinoma staging; MR enterography for Crohn.
• Angiography: vascular disease, obscure GI bleeding; therapeutic (chemoembolization, embolization of bleeding vessels, dilation).

Basic descriptive terms (barium study)

• Mucosal pattern: normal smooth/continuous; abnormal = disrupted, thickened, irregular.
• Ulceration: a breach of the mucosal surface → outward projection in profile; rounded barium collection en face.
• Filling defect: any process preventing normal filling of the lumen. Three types: intraluminal (surrounded by barium), intramural (not completely surrounded), extramural (compressing from outside).
• Stricture: tapering ends (benign) vs abrupt ends with overhanging edges/shouldering (malignant).

Esophagus

• Normal: three or four long straight parallel lucent bands (mucosal folds); smooth outline; normal peristalsis; three indentations (aortic arch, left main bronchus, left atrium).
• Tertiary contractions: rippling of the wall, transitory.
• Esophageal carcinoma: three patterns — annular constricting lesion (irregular ulcerated stricture, most common), polypoid (intraluminal filling defect), infiltrative (submucosal, simulates benign stricture). Malignant stricture = abrupt narrowing, irregular mucosa, prominent shoulders.
• Reflux esophagitis/benign stricture: distal esophagus, tapered, smooth, circumferential.
• Achalasia: failure of relaxation at the cardia sphincter; smooth tapered narrowing at the lower end; upstream dilation with food residue; decreased/absent peristalsis.
• Esophageal diverticulum: saccular outpouching with mucosa folds extending into the pouch; Zenker's diverticulum = weakness in the inferior constrictor muscle.
• Esophageal varices: serpiginous filling defects (rosary beads); change with intrathoracic pressure and peristalsis; portal hypertension — most commonly lower third; grades 1–2.

Stomach

• Anatomy: cardia, fundus, body, antrum; gastric rugae; areae gastricae; incisura; duodenal bulb.
• Well-distended stomach wall ≈ 5 mm on CT.
• Peptic ulcer: barium collection within the ulcer crater.
• Benign ulcer signs: projection beyond the lumen of the stomach; ulcer collar (smooth thickened lucent band of edematous wall); Hampton line (thin sharp lucent line traversing the orifice); ulcer mound (smooth sloping edematous tissue); radiating smooth folds extending to the crater edge; incisura defect (spastic indentation on the greater curvature opposite a lesser-curvature crater); site: lesser curvature; peristalsis normal/increased.
• Malignant ulcer: ulcer within a gastric mass (usually carcinoma); intraluminal (does not protrude outside); nodular, rolled, irregular or shouldered edges; mucosal folds obliterate before the crater edge; Carman meniscus sign (semicircular ulcer, inner margin convex toward the lumen, surrounded by radiolucent elevated ridge of neoplastic tissue); site: greater curvature; decreased peristalsis; rigid gastric wall.

Benign vs malignant gastric ulcer (comparison table)

Duodenal ulcer

• >95% in the duodenal bulb; H. pylori in >95%; almost always benign.
• Ulcer crater (barium collection), thickened folds, spasm and deformity of the bulb; chronic ulcer → cloverleaf deformity (symmetric) or pseudodiverticulum (asymmetric).

Gastric carcinoma

• Most common malignancy of the stomach; spread by local extension, distant metastases, drop metastases to ovaries.
• Early gastric cancer (EGC): invades no deeper than the submucosa (T1, any N). Types: I elevated (>5 mm, polypoid), II superficial, III shallow irregular ulcer.
• Advanced patterns: polypoid mass (lobulated filling defect), focal constricting lesion (annular filling defect), linitis plastica (leather-bottle stomach — thickening, rigidity, diffuse irregular narrowing).
• Malignant ulcer of gastric leiomyosarcoma: intramural origin, obtuse angle with normal gastric wall.

Small bowel

• Small bowel follow-through; enteroclysis (nasoduodenal tube past the pylorus); ring/spring mucosal folds; stenosis, polyps, mucosal alterations, terminal ileitis.

Colon

• Length variable; caliber decreases from cecum to sigmoid; haustra throughout.
• Diverticulosis: multiple round/oval outpouchings of barium projecting beyond the lumen (profile) or ring-like lesions (en face); criss-crossing ridges of thickened circular muscle (sawtooth).
• Polyp: focal protruded lesion; sessile plaque, sessile hemisphere, pedunculated sphere.
• Colorectal carcinoma: commonest in rectosigmoid and cecum. Three types: annular carcinoma (irregular stricture, shelf-like margin), polypoid/fungating (irregular filling defect), ulcerating (intraluminal ulcer). CT: bowel wall thickening + irregular lumen narrowing; MRI: high-resolution T2 for rectal staging (mesorectal fat and fascia).

Hiatus hernia and diverticula

• Sliding hiatus hernia (common): GEJ + portion of stomach above the diaphragm; reflux. Rolling (para-esophageal): GEJ below diaphragm, stomach herniates above.
• Duodenal diverticulum: medial border of descending duodenum, periampullary (62% 2nd part); smooth rounded with narrow neck.
• Gastric diverticulum: 75% posterior wall of fundus.

High-Yield Points

• Key Point: Water-soluble contrast for suspected perforation; barium for routine studies (peritonitis risk if it leaks).
• Key Point: Filling defect types: intraluminal (surrounded), intramural (partially), extramural (compressing).
• Key Point: Benign stricture = tapered; malignant = abrupt with shoulders.
• Key Point: Benign ulcer = extraluminal, folds radiate to crater, Hampton line/collar; malignant ulcer = intraluminal, folds obliterate, Carman meniscus.
• Key Point: Achalasia = smooth tapered distal narrowing + upstream dilation; varices = serpiginous filling defects (rosary).
• Key Point: Linitis plastica = leather-bottle stomach (diffuse infiltration).
• Key Point: Colorectal carcinoma commonest in rectosigmoid + cecum; annular = apple-core with shelf.

Topic Summary

GI barium studies test three basic signs: ulceration (outward projection), filling defect (intraluminal/intramural/extramural) and stricture (tapered vs shouldered). The benign vs malignant gastric ulcer differentiation is the single most examinable table. Esophageal disease (carcinoma, achalasia, varices, Zenker's), gastric carcinoma patterns (polypoid, annular, linitis plastica, EGC types), duodenal ulcer deformity, colonic diverticulosis/polyps/carcinoma and hiatus hernia round out the chapter. CT stages malignancy; MRI excels at rectal staging; water-soluble contrast is for perforation.