Comprehensive Notes on Radiology Diagnosis

Chest Radiograph Interpretation Skills

  • Chest radiographs are challenging due to overlapping imaging features and reliance on four densities: air, fat, soft tissue/water, and bone/metal.
  • A systematic approach to interpreting chest radiographs is crucial. A typical search pattern includes scrutinizing the cardiomediastinal silhouette, lung parenchyma, intercostal spaces, bones, and area under the diaphragm.
  • Overlapping imaging features and superimposed shadows can make chest radiographs challenging to interpret. Some overlapping imaging features include atelectasis, pleural effusion, or pulmonary edema.
  • Diagnostic certainties on chest radiograph:
    • Focal airspace opacity with air bronchograms is diagnostic of pneumonia.
    • Meniscus sign indicates a pleural effusion.
    • Plate-like or linear opacities in both lung bases are likely atelectasis.
    • Cardiomegaly, effusion, and Kerley B lines indicate pulmonary edema.
    • Golden S sign indicates right upper lobe collapse.

Differentiating Atelectasis from Effusion

  • Complete opacification of the lung can be due to either atelectasis or effusion.
  • Atelectasis:
    • Loss of volume, leading to collapse.
    • Ipsilateral shift of the trachea (deviation towards the side of the whiteout).
  • Effusion:
    • Complete opacification due to fluid accumulation.
    • Contralateral shift of the trachea (deviation away from the side of the whiteout) due to mass effect.

Pulmonary Metastases

  • Multiple pulmonary nodules and masses should raise suspicion for pulmonary metastases.

CT vs. Chest Radiographs

  • CT has superior contrast discrimination and diagnostic ability compared to chest radiographs.
  • If a clinical difference exists and the patient is symptomatic with high clinical suspicion, a CT scan should be obtained.
  • Tree-in-bud opacities:
    • Irregular or nodular branching patterns representing dilated and impacted centrilobular bronchioles.
    • Suggestive of infection, airway disease, allergic bronchopulmonary aspergillosis, or aspiration.
  • Ground glass opacity:
    • Increased or hazy attenuation of the lung without obscuring underlying vessels.
    • Caused by replacement of alveoli by fluid, cells, or fibrosis.

Importance of Multiple Views

  • One view is no view. Having multiple views improves diagnostic certainty and capability.
  • Spine sign: Increased density down the vertebral bodies due to a focal opacity, indicating a left lower lobe pneumonia.

Tubes and Lines

  • Endotracheal tube: Should terminate in the midline trachea, 4-5 cm above the carina.
  • Enteric tube: Should course along the esophagus, with the side port and tip below the GE junction.
  • EKG leads: External to the patient, not following any anatomical course, attached to EKG lead pads.
  • Concerning finding is a malpositioned feeding tube in the right main stem bronchus, requiring repositioning.
  • Distal positioning of a feeding tube can cause perforation of small bronchioles, leading to tension pneumothorax upon removal; thoracic surgery consultation recommended.
  • Swan-Ganz catheter: If too far peripherally located in the distal right pulmonary artery, it needs repositioning.
  • Extrapleural course of a chest tube can occur. CT scan may be needed to diagnose.
  • Right chest tube can be misplaced through the liver and into the intrahepatic IVC, requiring IR for removal.

Can't Miss Radiology Diagnoses

  • Tension Pneumothorax:
    • Ipsilateral increase in intercostal spaces.
    • Contralateral mediastinal shift due to mass effect.
    • Depression of the diaphragm.
  • Pneumothorax:
    • Visceral pleural line formed by the collapsed lung.
    • Absence of lung markings peripheral to the visceral pleural line.
    • Skin folds can mimic pneumothoraces but will show preserved lung markings peripheral to the line.
  • Free Subdiaphragmatic Air (Pneumoperitoneum):
    • Upright radiographs (chest or abdomen) are helpful in identifying air.
    • CT can show the site of perforation.
    • Common causes include perforated peptic ulcer, diverticulitis, and bowel ischemia.
    • Wriggler sign: Air on both sides of the bowel wall depicted on supine radiographs.

Small Bowel Obstructions (SBO)

  • Dilated loops of small bowel (≥3 cm).
  • Air-fluid levels on upright radiograph.
  • Valvulae conniventes (lines going all the way across the bowel wall) differentiate small from large bowel (haustra).
  • CT is used to look for the underlying etiology.
  • Adhesive SBO pathway involves conservative management with NG tube and oral contrast, monitoring contrast progression to the colon within 24 hours.

Saddle Pulmonary Embolism

  • Filling defects within the pulmonary artery.
  • Assess for right heart strain (right ventricle larger than the left).

Aortic Dissection

  • Type A involves the ascending aorta.
  • Type B involves the descending aorta.
  • Ruptured Abdominal Aortic Aneurysm:
    • Break in the aortic wall.
    • Active extravasation on contrast-enhanced imaging.

Intracranial Hemorrhage

  • Subarachnoid hemorrhage: Blood interdigitating the sulci on non-contrast CT.
  • Subdural hemorrhage: Extra-axial, crescentic hyperdense hemorrhage.
  • Look for mass effect, midline shift, and herniation.
  • Repeat head CT in 4-6 hours to assess for complications or increased bleeding.

Imaging Protocols and Considerations

  • The ACR Appropriateness Criteria assists physicians in making appropriate imaging decisions.
  • Detailed history and clinical question help radiologists protocol CT studies accurately.
  • PE vs. Dissection: Prioritize based on clinical suspicion due to different opacification timing.

Use of Oral and IV Contrast for CT

  • Oral Contrast:
    • May not be necessary for all CT abdomen/pelvis patients, particularly those with BMI > 25.
    • Can obscure mucosal enhancement in ischemic bowel.
    • Consider in post-operative patients within 30 days, penetrating trauma, or surgeon request.
  • IV Contrast:
    • Essential for diagnosing conditions like renal infarcts, abscesses, and pseudoaneurysms.
    • Renal stones can be visualized without contrast, but IV contrast helps evaluate other organs for pain source.
    • Dual-energy CT can differentiate uric acid from calcium-based stones.

Renal Failure and Contrast Allergy Patients

  • Contrast-induced nephropathy is rare; GFR ≥ 30 is generally used as a threshold.
  • Benefits of contrast should outweigh risks; risk factors may warrant renal function assessment.
  • Dialysis patients can receive IV contrast.
  • Allergic Reactions: Premedication with prednisone and Benadryl protocols exist, but these do not prevent all reactions.