Diagnostic Radiology
Core Concepts
Diagnostic radiology questions test your ability to recognize patterns, understand modality strengths and limitations, and apply systematic search patterns. You must know the classic radiographic signs (e.g., air bronchogram, silhouette sign, Kerley B lines), the difference between sensitivity and specificity of modalities (e.g., CT for renal stones, MRI for soft tissue), and the ACR Appropriateness Criteria for common scenarios.
Common Traps
Questions often present a finding that is pathognomonic but ask for the next step or the underlying cause. For example, a “double bubble” sign in a neonate suggests duodenal atresia, but the question may ask which associated anomaly to look for (e.g., Down syndrome, VACTERL). Another trap is confusing the modality of choice: ultrasound is preferred for gallstones and pediatric pyloric stenosis, while CT is preferred for diverticulitis and renal colic. Also, beware of “always” or “never” answer choices-radiologic findings are rarely absolute.
Worked Example
A 45-year-old woman presents with right upper quadrant pain and fever. Ultrasound shows gallbladder wall thickening and pericholecystic fluid. The most likely diagnosis is acute cholecystitis. The sonographic Murphy sign is highly specific. If the question asks for the best initial imaging test for suspected acute cholecystitis, the answer is ultrasound, not CT. Rule of thumb: for right upper quadrant pain, start with ultrasound; for left lower quadrant pain, start with CT.
Key Points
- Know the classic signs and their associated diseases.
- Understand modality strengths: US for gallbladder, CT for acute abdomen, MRI for brain and spine.
- Apply systematic search patterns (e.g., ABCDE for chest X-ray).
- Avoid absolute statements; consider clinical context.