A 52-year-old obese woman presents with severe right upper-quadrant pain, fever, and positive Murphy's sign. Transabdominal ultrasound is performed. The structure marked **B** in the diagram shows an echogenic stone with posterior acoustic shadowing impacted at the neck of the gallbladder. Which of the following best explains why this finding is the pathophysiological basis for acute calculous cholecystitis in this patient?
A. Posterior acoustic shadowing is pathognomonic for infected bile and indicates the presence of gas-forming organisms within the gallbladder lumen
B. Impaction of the stone at the gallbladder neck causes mechanical obstruction of the cystic duct, leading to bile stasis, increased intraluminal pressure, and secondary bacterial infection
C. The echogenic appearance of the stone indicates cholesterol composition, which triggers an inflammatory cascade independent of ductal obstruction
D. The stone's location at the neck prevents normal gallbladder contractility, but inflammation occurs only if the stone migrates into the common bile duct
Explanation
Why option 1 is correct
The echogenic stone with posterior acoustic shadowing impacted at the gallbladder neck (structure B) causes mechanical obstruction of the cystic duct. This obstruction leads to bile stasis, increased intraluminal pressure, mucosal ischemia, and bacterial translocation—the classic pathophysiological sequence of acute calculous cholecystitis as described in Sabiston. The clinical presentation (fever, elevated WBC, CRP, positive Murphy's sign) and the positive sonographic Murphy's sign directly correlate with this obstruction-induced inflammation. The stone's position at the neck is the critical anatomical factor that distinguishes acute cholecystitis from asymptomatic cholelithiasis (which this patient had for 8 months prior).
Why each distractor is wrong
Option 2: While the stone may be cholesterol-based, the echogenic appearance and acoustic shadowing are ultrasound properties that do not themselves trigger inflammation. Inflammation is secondary to obstruction, not to stone composition alone. Asymptomatic stones with identical composition do not cause cholecystitis.
Option 3: Posterior acoustic shadowing is a normal ultrasound artifact caused by sound wave attenuation through the calcified stone—it does not indicate gas-forming organisms or infected bile. Pneumocholecystitis would show gas within the gallbladder wall or lumen on imaging, which is not described here.
Option 4: Although the stone's location does impair contractility, acute cholecystitis does NOT require migration into the common bile duct. Obstruction at the cystic duct (neck position) is sufficient to cause acute cholecystitis. Migration into the CBD would cause obstructive jaundice and choledocholithiasis, a different entity. This patient's bilirubin is only mildly elevated (1.6 mg/dL), consistent with cystic duct obstruction, not CBD obstruction.
High-YieldNEET PG
Acute calculous cholecystitis = cystic duct obstruction by stone (usually at the neck or Hartmann's pouch) → bile stasis → increased pressure → ischemia → inflammation ± secondary infection. The stone does NOT need to be in the CBD.
Sabiston Textbook of Surgery, 21st Edition, Chapter on Biliary System
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