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Difficulty: MediumOrdering Imaging Studies

Evaluate the following clinical scenarios and match each patient presentation with the most appropriate next step in diagnostic imaging.

  • An obstetric patient at 14 weeks gestation presenting with acute right lower quadrant pain, fever, and leukocytosis. An initial graded compression abdominal ultrasound fails to visualize the appendix.Magnetic resonance imaging of the abdomen and pelvis without contrast
  • An unrestrained driver involved in a high-speed vehicle rollover who arrives at the emergency department hypotensive (blood pressure 75/40 mmHg) and tachycardic, with a rigid and distended abdomen.Bedside focused assessment with sonography for trauma (FAST)
  • An older adult with a legacy (non-MRI conditional) dual-chamber pacemaker who develops sudden-onset saddle anesthesia, bilateral lower extremity weakness, and urinary retention.Computed tomography myelography of the lumbar spine
  • A middle-aged adult with persistent postprandial right upper quadrant pain and fever. Initial right upper quadrant ultrasound demonstrates cholelithiasis but shows normal gallbladder wall thickness and no pericholecystic fluid.Hepatobiliary iminodiacetic acid (cholescintigraphy) scan

Answer

The pregnant patient requires MRI without contrast to avoid radiation. The unstable trauma patient requires bedside FAST to prevent delayed stabilization. The patient with a legacy pacemaker requires CT myelography due to MRI contraindications. The patient with an equivocal ultrasound for cholecystitis requires a HIDA scan for definitive functional assessment.
Each correct pairing optimizes diagnostic accuracy while adhering to critical safety constraints: utilizing bedside ultrasound for unstable trauma, selecting radiation-free MRI for pregnant patients, using CT myelography when MRI is contraindicated, and relying on nuclear medicine to functionally confirm cholecystitis when anatomical ultrasound is ambiguous.

Step-by-Step Solution

1
Assess the pregnant patient with suspected appendicitis and a non-diagnostic ultrasound.
Select MRI without contrast.
Computed tomography exposes the fetus to ionizing radiation, whereas MRI is safe and provides excellent soft-tissue resolution for appendicitis in pregnancy.
2
Evaluate the hemodynamically unstable trauma victim with a rigid abdomen.
Select bedside focused assessment with sonography for trauma (FAST).
Transporting an unstable patient to the CT scanner can result in fatal delays. FAST is rapidly performed at the bedside to detect free fluid.
3
Identify the appropriate imaging for suspected cauda equina syndrome in a patient with a non-MRI conditional pacemaker.
Select CT myelography of the lumbar spine.
Standard MRI is strictly contraindicated due to the legacy pacemaker. CT myelography provides the necessary visualization of the spinal canal and nerve roots.
4
Determine the next step for clinically suspected acute cholecystitis with an indeterminate ultrasound.
Select Hepatobiliary iminodiacetic acid (HIDA) scan.
Ultrasound is highly sensitive for gallstones but less specific for acute cholecystitis. A HIDA scan evaluates cystic duct patency and functionally confirms the diagnosis.

Key Concept

Selecting the appropriate imaging modality requires balancing diagnostic yield against patient stability, physiologic state (e.g., pregnancy), and absolute contraindications (e.g., legacy implanted electronic devices).
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Ordering Imaging Studies

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