Radiographic Anatomy

Radiographic Anatomy - X-Ray Vision Quest

• X-rays: electromagnetic radiation. Images from differential tissue absorption; denser tissues absorb more.

• Key Terminology:

  • Radiolucent: Darker (black/grey); X-rays pass easily (e.g., air in lungs).
  • Radiopaque: Brighter (white); X-rays absorbed/attenuated (e.g., bone, metal).

• Five Basic Radiodensities (Order: Least to Most Dense): 📌 Mnemonic: "All Fat Women Buy Metal"

  Substance	Appearance on X-ray	Example
  Air	Black	Lungs, bowel gas
  Fat	Dark Grey	Subcutaneous fat
  Water/Soft Tissue	Grey	Muscle, organs
  Bone (Calcium)	Light Grey/White	Skeleton
  Metal	Bright White	Implants, contrast

⭐ Chest X-ray (CXR): Posteroanterior (PA) view is preferred over Anteroposterior (AP) to reduce cardiac magnification and improve lung clarity.

Radiographic Anatomy - Chest Case Clues

Systematic CXR Interpretation (📌 ABCDE):

• Airway: Trachea (midline), carina, main bronchi.
• Breathing (Lungs & Pleura):
  • Lungs: Symmetry; opacities (consolidation), lucencies (pneumothorax); vascular markings.
  • Pleura: Effusion (blunted costophrenic angles), pneumothorax.
• Circulation (Heart & Mediastinum):
  • Heart: Size (Cardiothoracic Ratio $CTR < \textbf{0.5}$), shape, borders.
  • Mediastinum: Width, contours (aortic knob), hila.
• Diaphragm: Position (R higher), shape, free air? Costophrenic angles (sharp).
• Everything Else: Bones (ribs, clavicles: fractures, lesions), soft tissues, lines/tubes.

⭐ Silhouette Sign: Loss of a normal border between structures (e.g., heart/diaphragm and lung) indicates the pathology is adjacent and in the same plane.

Radiographic Anatomy - Belly Map Mysteries

Systematic Abdominal X-Ray (AXR) Review:

• Bones: Check for fractures, lytic/sclerotic lesions.
• Stones: Identify radio-opaque renal, gallstones, appendicoliths.
• Gas: Evaluate bowel gas pattern, look for free air.
  • 📌 3-6-9 Rule: Small bowel < 3 cm, Large bowel < 6 cm, Cecum < 9 cm.
• Mass: Note organomegaly (liver, spleen, kidneys), soft tissue masses.
• Organs: Assess liver, spleen, kidneys, psoas shadows.

Common Gas Patterns & Significance:

Radiographic Anatomy - Bone Zone Views

Standard: 2 views (AP & Lateral, 90° to each other). Include joint above & below. Consider comparison views for peds/subtle cases. Describing a fracture:

• Location: Bone; Epiphysis, Metaphysis, Diaphysis. Intra-articular?
• Type: e.g., Transverse, Oblique, Spiral, Comminuted, Greenstick, Avulsion.
• Displacement: Distal fragment shift (direction, amount e.g., 50% posterior).
• Angulation: Distal fragment tilt (degree, apex direction e.g., 20° apex volar).
• Rotation: Axial twist (clinical assessment often key). 📌 SALTR-Harris (physeal injuries):
  • I: Slipped (physis)
  • II: Above (physis + metaphysis)
  • III: Lower (physis + epiphysis)
  • IV: Through (all three: physis, metaphysis, epiphysis)
  • V: Rammed (crush of physis)

⭐ A visible posterior fat pad or displaced anterior fat pad ("sail sign") in an adult elbow X-ray often indicates an occult intra-articular fracture (e.g., radial head).

High‑Yield Points - ⚡ Biggest Takeaways

• Chest X-ray interpretation (PA view preferred) requires a systematic approach (ABCDEs).
• CT is superior for bone detail, acute hemorrhage, and complex fractures; uses ionizing radiation.
• MRI excels in soft tissue contrast (brain, spine, joints) and uses no ionizing radiation.
• Barium studies visualize the GI tract; iodinated contrast is used for vessels (angiography) and urinary tract (IVU).
• Ultrasound is often first-line for gallbladder, pelvic organs, pregnancy, and guiding interventions; it's non-ionizing.
• Key signs: Kerley B lines (pulmonary edema), air-fluid levels (bowel obstruction), free subdiaphragmatic air (perforation).