Diagnostic Radiology Across Organ Systems
Core concepts
Integrate modality choice with disease pattern. In chest imaging, know the lobar anatomy, silhouette sign, air bronchograms, and the difference between interstitial and alveolar patterns. In abdominal imaging, know the acute abdomen pathways (ultrasound first for biliary and pelvic pain, CT for suspected obstruction or perforation), the CT signs of bowel ischemia, and the appearance of common tumors. In neuroradiology, know stroke windows, hemorrhage vs infarct on CT, and the role of MRI diffusion. In musculoskeletal imaging, know fracture descriptions, the Salter-Harris classification, and the appearance of arthritis patterns. Pediatric and obstetric considerations require lower-dose strategies.
Traps
Questions often test the first-line study rather than the most sensitive study. For suspected acute cholecystitis, ultrasound is first-line; for suspected appendicitis in adults, CT is often preferred, while ultrasound or MRI may be preferred in children and pregnancy. Do not confuse the silhouette sign (loss of border with adjacent opacity) with air bronchograms (air-filled bronchi outlined by consolidation). In stroke, noncontrast CT excludes hemorrhage before thrombolysis; diffusion MRI detects early infarct. In bone, a lytic lesion in an adult suggests metastasis or myeloma, while in a child consider Langerhans cell histiocytosis or infection.
Worked example
A patient with right upper quadrant pain, fever, and a positive Murphy sign: the best initial study is right upper quadrant ultrasound, which may show wall thickening, pericholecystic fluid, and stones. CT is reserved for complications or equivocal cases. Choosing CT first because it is "more sensitive" is a classic distractor.