What are the correct matches for the radiological signs with their associated intestinal pathologies: string of pearls sign, comb sign, accordion sign, and Rigler's sign, with small bowel obstruction, Crohn's disease, pseudomembranous colitis, and pneumoperitoneum?

Radiological Signs and Their Associated Intestinal Pathologies

The correct answer is D) 1-d, 2-b, 3-a, 4-c, matching string of pearls sign with small bowel obstruction, comb sign with Crohn's disease, accordion sign with pseudomembranous colitis, and Rigler's sign with pneumoperitoneum.

Detailed Explanation of Each Sign

1. String of Pearls Sign → Small Bowel Obstruction (d)

• The string of pearls sign appears on upright abdominal radiographs as small gas bubbles trapped between valvulae conniventes in fluid-filled dilated small bowel loops, creating a characteristic appearance resembling a string of pearls 1
• This sign is highly specific for small bowel obstruction when air-fluid levels of differential height are present in the same bowel loop 1
• CT demonstrates this as small pockets of gas within fluid-distended small bowel at the transition point of obstruction 2

2. Comb Sign → Crohn's Disease (b)

• The comb sign represents prominent vasa recta (mesenteric vessels) that appear as parallel lines extending perpendicular to inflamed bowel loops, resembling the teeth of a comb 3
• This finding reflects increased vascularity and hyperemia in the mesentery adjacent to actively inflamed bowel segments in Crohn's disease 3
• The comb sign is associated with perienteric edema/inflammation and increased attenuation in mesenteric fat on CT 3
• This sign is particularly prominent along the mesenteric border where Crohn's disease inflammation is typically more severe 3

3. Accordion Sign → Pseudomembranous Colitis (a)

• The accordion sign appears on CT as marked thickening of haustral folds with contrast material trapped between them, creating an appearance similar to an accordion's bellows
• This sign is characteristic of pseudomembranous colitis caused by Clostridium difficile infection
• The alternating pattern of thickened edematous mucosa and contrast-filled haustra creates the distinctive accordion appearance

4. Rigler's Sign → Pneumoperitoneum (c)

• Rigler's sign (also called the double wall sign) occurs when free intraperitoneal air outlines both sides of the bowel wall, making it visible as a distinct line on plain radiographs
• This sign indicates pneumoperitoneum from bowel perforation
• Both the luminal and serosal surfaces of the bowel wall become visible when surrounded by gas on both sides

Clinical Implications

For Small Bowel Obstruction Recognition

• When evaluating suspected obstruction, look for the string of pearls sign on upright films combined with air-fluid levels of differential height (≥25 mm width) to distinguish high-grade from low-grade obstruction 1
• CT is superior to plain films for determining the level and cause of obstruction, with 93% sensitivity and 100% specificity 2

For Crohn's Disease Assessment

• The comb sign indicates active inflammation and should prompt careful evaluation for other signs of severe disease including wall thickening, ulcerations, and penetrating complications 3
• MR enterography or CT enterography should assess for asymmetric mesenteric border inflammation, which is highly specific for Crohn's disease 3
• Additional findings to report include fibrofatty proliferation ("creeping fat"), strictures, and fistulas 3, 4

Common Pitfalls to Avoid

• Do not confuse mesenteric fat stranding (acute inflammation) with fibrofatty proliferation (chronic "creeping fat") - the former appears as hazy increased density while the latter displaces bowel loops 4
• In Crohn's disease with obstruction, differentiate CD-related strictures from adhesive obstruction by identifying the comb sign and other inflammatory findings at the transition zone 5
• The string of pearls sign requires upright positioning to visualize properly; supine films alone may miss this finding 1