A 19-year-old woman with 22 hours of right iliac fossa pain, fever (38.1°C), and positive Rovsing's sign undergoes graded-compression ultrasonography of the right iliac fossa. The structure marked **A** in the ultrasound image is non-compressible and measures greater than 6 mm in outer diameter. Which of the following best describes why this finding is the single most important diagnostic criterion for acute appendicitis on ultrasound?

Question

Accepted Answer

A. The non-compressible blind-ending tubular structure with outer diameter >6 mm is pathognomonic for acute appendicitis, as the normal appendix is compressible and measures <6 mm. ## Why option 1 is correct The non-compressible blind-ending tubular structure with outer diameter >6 mm is the single most important ultrasound criterion for diagnosing acute appendicitis. According to Sabiston Textbook of Surgery, the normal appendix is compressible and measures <6 mm in outer diameter. When the appendix becomes inflamed (acute appendicitis), it loses compressibility due to wall edema and rigidity, and the outer diameter increases to >6 mm. This combination—non-compressibility AND diameter >6 mm—is the primary diagnostic criterion that distinguishes acute appendicitis from a normal appendix on graded-compression ultrasonography. The patient's clinical presentation (Rovsing's sign positive, fever, elevated WCC and CRP) combined with this ultrasound finding established the diagnosis with sufficient confidence to proceed directly to surgery. ## Why each distractor is wrong - **Option 2**: While the target appearance (concentric echogenic and hypoechoic rings) on transverse view is a supportive finding indicating wall thickening and inflammation, it is NOT the single most important criterion. The target sign is seen in other inflammatory bowel conditions and is less specific than the combination of non-compressibility and diameter >6 mm. - **Option 3**: The hyperechoic inflamed periappendiceal fat (structure C) is a supportive finding but is neither the most important nor the most sensitive criterion. It reflects secondary inflammation and is less specific than the primary appendiceal diameter and compressibility findings. - **Option 4**: The absence of free fluid collection (structure D) is important for determining whether perforation has occurred, but it does NOT establish the diagnosis of acute appendicitis itself—it merely excludes complicated (perforated) appendicitis. A non-perforated appendix can still be acutely inflamed without free fluid. **High-Yield:** On graded-compression ultrasound, acute appendicitis is diagnosed when the appendix is non-compressible AND measures >6 mm in outer diameter; the normal appendix is compressible and <6 mm. [cite: Sabiston Textbook of Surgery, 21st Edition, Chapter on Acute Appendicitis]

Answer

B. The target appearance on transverse view with concentric wall layers indicates transmural inflammation and is diagnostic of appendicitis

Answer

C. The surrounding hyperechoic inflamed periappendiceal fat is the most sensitive finding for distinguishing acute appendicitis from other causes of right iliac fossa pain

Answer

D. The absence of free fluid collection excludes perforation and confirms the diagnosis of non-perforated appendicitis

Explanation

Why option 1 is correct

Why each distractor is wrong

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