A 48-year-old woman presents to the emergency department with severe, constant right upper… — USMLE Step 3

A 48-year-old woman presents to the emergency department with severe, constant right upper quadrant abdominal pain that radiates to her right scapula, accompanied by fever and nausea. The pain began $12\text{ hours}$ ago after she consumed a high-fat meal. Her temperature is $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ ), blood pressure is $135/85\text{ mmHg}$ , and heart rate is $105\text{/min}$ . Physical examination reveals marked tenderness with inspiratory arrest upon deep palpation of the right upper quadrant.

Arrange the following diagnostic imaging modalities in the appropriate step-wise sequence for evaluating and managing this patient's presentation, from the initial diagnostic test to the evaluation of potential late complications.

1Right upper quadrant transabdominal ultrasonography
2Hepatobiliary iminodiacetic acid (HIDA) cholescintigraphy scan
3Contrast-enhanced computed tomography (CT) of the abdomen

Answer

The correct sequence for evaluating suspected acute cholecystitis is right upper quadrant transabdominal ultrasonography first, followed by a HIDA scan if the ultrasound is indeterminate, and finally a CT scan of the abdomen to evaluate for complications if clinical deterioration occurs.

The standard diagnostic algorithm for acute cholecystitis begins with right upper quadrant transabdominal ultrasonography. Ultrasound is rapid, lacks ionizing radiation, and is highly sensitive for detecting gallstones, which are the primary etiology. If the ultrasound findings are equivocal (e.g., gallstones are present but wall thickening or sonographic Murphy sign is absent), a hepatobiliary iminodiacetic acid (HIDA) scan is ordered next. The HIDA scan assesses cystic duct patency, and failure of the gallbladder to visualize confirms the diagnosis of acute cholecystitis. Finally, if a patient with acute cholecystitis subsequently exhibits clinical deterioration, severe sepsis, or generalized peritonitis, a contrast-enhanced CT of the abdomen is then indicated to evaluate for complications such as gallbladder perforation, gangrenous cholecystitis, or pericholecystic abscess formation.

Step-by-Step Solution

Analyze the clinical presentation

The patient's postprandial right upper quadrant pain, fever, and positive Murphy sign strongly suggest acute cholecystitis.

Identifying the suspected primary diagnosis dictates the initiation of a specific imaging algorithm.

Determine the optimal first-line imaging test

Right upper quadrant transabdominal ultrasonography is placed first in the sequence.

Ultrasound is the most sensitive initial test for gallstones and local gallbladder inflammation, making it the universal first step.

Identify the appropriate confirmatory test for an equivocal initial result

A HIDA (cholescintigraphy) scan is placed second.

If the ultrasound cannot definitively confirm or rule out acute cholecystitis, a HIDA scan is utilized to demonstrate cystic duct obstruction (non-visualization of the gallbladder).

Select the imaging modality for suspected downstream complications

Contrast-enhanced CT of the abdomen is placed third.

CT is not utilized for initial diagnosis but is highly effective for identifying severe downstream complications like perforation or abscess if the patient clinically deteriorates.

Key Concept

Step-wise diagnostic imaging algorithm for acute cholecystitis

Alternative Method

Point-of-care ultrasonography (POCUS) performed immediately by the attending physician can rapidly identify gallstones and a sonographic Murphy sign at the bedside, accelerating the decision to consult general surgery before a formal, comprehensive radiology-performed ultrasound is completed.

Estimated Time:1m 0s

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