The Common Vein

• • • Etymology
      Derived from the Greek word “embolus,” meaning a plug or stopper, and “pulmonis,” referring to the lungs.
    • AKA
      PE, lung embolism
    • What is it?
      Pulmonary embolism (PE) is the obstruction of one or more pulmonary arteries, most commonly caused by a thrombus originating in the deep veins of the lower extremities. It can also result from non-thrombotic emboli, such as fat, air, amniotic fluid, tumor fragments, septic emboli, or paradoxical emboli.
    • Caused by
      • Most common cause
        • Deep vein thrombosis (DVT)
      • Other causes include
        • Thrombotic causes
          • Deep vein thrombosis
          • Upper extremity thrombi or central line-associated clots
        • Non-thrombotic causes
          • Fat embolism (e.g., long bone fractures)
          • Air embolism (e.g., trauma, surgical procedures)
          • Amniotic fluid embolism (e.g., labor and delivery)
          • Tumor embolism (e.g., malignancy-related)
          • Septic emboli (e.g., endocarditis, infected thrombophlebitis)
          • Foreign bodies (e.g., catheter fragments, embolized devices)
        • Paradoxical embolus
          • May occur secondary to a PE, where elevated right-sided pressures create a right-to-left shunt through a patent foramen ovale (PFO) or atrial septal defect (ASD).
    • Resulting in
      • Vascular obstruction and impaired gas exchange
      • Increased right ventricular afterload and potential strain or failure
      • Hypoxemia due to ventilation-perfusion mismatch
    • Structural changes
      • Obstruction of pulmonary arteries with potential ischemia in downstream lung parenchyma
      • Infarction occurs only if collateral circulation is inadequate
    • Pathophysiology
      • Emboli obstruct pulmonary blood flow, increasing pulmonary vascular resistance and right ventricular afterload.
      • Ventilation-perfusion mismatch leads to hypoxemia.
      • Infarction is rare due to dual blood supply (pulmonary and bronchial arteries) unless collateral circulation is compromised.
    • Pathology
      • Acute emboli: Central or peripheral thrombi causing vascular occlusion, vessel dilation, and ischemia.
      • Chronic emboli: Fibrotic, calcified clots or web-like structures causing vascular remodeling and pulmonary hypertension.
    • Diagnosis
      • Clinical
        • Symptoms: Acute onset of dyspnea, pleuritic chest pain, hemoptysis, or syncope.
        • Signs: Tachypnea, tachycardia, hypoxemia, and, in severe cases, hypotension or shock.
      • Radiology
        • Imaging plays a key role in confirming the diagnosis.
      • Labs
        • Elevated D-dimer levels (sensitive but non-specific).
        • Arterial blood gases may show hypoxemia and respiratory alkalosis.
    • Management
      • Acute phase
        • Anticoagulation (e.g., heparin, direct oral anticoagulants)
        • Thrombolysis for massive PE with hemodynamic instability
        • Catheter-directed therapies or surgical embolectomy in select cases
      • Chronic phase
        • Long-term anticoagulation to prevent recurrence
        • Inferior vena cava (IVC) filters for anticoagulation contraindications
    • Radiology Detail
      • CXR
        • Findings
          • Normal in most cases
          • Subtle signs: Westermark sign (vascular cut-off), Hampton hump (wedge-shaped opacity), pleural effusion
        • Associated Findings
          • Enlarged pulmonary artery or right heart silhouette
      • CT Pulmonary Angiography (CTPA)
        • Parts
          • Main pulmonary arteries, segmental and subsegmental branches
        • Size
          • Emboli range from small subsegmental clots to large central occlusions
        • Shape
          • Central or eccentric filling defects
        • Position
          • Central (main or lobar arteries) or peripheral (segmental or subsegmental branches)
        • Character
          • Acute vs. Chronic Emboli
            • Acute: Central filling defects with vessel enlargement and sharply defined edges
            • Chronic: Eccentric filling defects with wall thickening, calcifications, or web-like structures
          • Occlusive vs. Non-occlusive
            • Occlusive: Complete vessel obstruction, leading to severe perfusion defects
            • Non-occlusive: Partial obstruction with milder perfusion defects
          • Septic Emboli
            • May cavitate, often presenting with peripheral nodules or wedge-shaped opacities, sometimes associated with abscess formation
          • Fat and Amniotic Fluid Emboli
            • Typically do not appear as filling defects due to involvement of small pulmonary vessels
            • Fat emboli: Diffuse ground-glass opacities with interlobular septal thickening
            • Amniotic fluid emboli: Bilateral ground-glass opacities and consolidations, mimicking ARDS
          • Dual-Energy CT and Iodine Maps
            • Identifies perfusion defects in affected lung regions
            • Useful in assessing regional perfusion and in equivocal cases
          • Right Heart Strain
            • Septal findings: Straightening or bowing of the interventricular septum toward the left ventricle
            • Preexisting conditions: LVH (reduces LV cavity size) and chronic pulmonary hypertension (enlarges RV) can affect RV/LV ratios
            • Reflux of contrast: Normal into IVC but abnormal into hepatic veins
            • Azygos vein enlargement: Reflects elevated RV pressure and systemic venous congestion
          • Feeding Vessel
            • A prominent vessel leading to a lesion suggests an embolus or vascular abnormality
        • V/Q Scan
          • Matched vs. Mismatched Defects
            • Matched defects: Ventilation and perfusion are both reduced, typically seen in parenchymal diseases.
            • Mismatched defects: Normal ventilation with perfusion defects, highly suggestive of PE.
          • Indications
            • Preferred in patients with contraindications to CTPA (e.g., contrast allergy, renal insufficiency, pregnancy).
            • Often used as a secondary test when CTPA is equivocal.
          • Radiation Dose
            • CTPA: 2?4 mSv (higher maternal chest dose).
            • V/Q Scan: 0.5?1.0 mSv (lower maternal chest dose but slightly higher fetal dose).
        • Time
          • Acute: Features of right heart strain and high clot burden
          • Chronic: Organized thrombi and signs of pulmonary hypertension
        • Associated Findings
          • Pulmonary infarction, pleural effusions, or wedge-shaped opacities
    • Recommendations
      • Perform CTPA for suspected PE when no contraindications exist.
      • Use Doppler ultrasound of lower extremities if CTPA is contraindicated.
        • If DVT is detected, initiate anticoagulation therapy and consider follow-up with V/Q scan.
      • V/Q scan is preferred in pregnant patients, particularly with normal chest X-ray findings.
    • Key Points and Pearls
      • PE requires rapid diagnosis and treatment to prevent mortality.
      • CTPA is the gold standard for detecting PE but is contraindicated in some patients.
      • V/Q scan is safer for pregnant patients due to lower maternal radiation exposure.
      • Septic, tumor, and paradoxical emboli should be considered in atypical cases.
      • Infarction is rare due to dual blood supply but occurs if collateral circulation is inadequate.

Radiation Dose and Preference in Pregnancy: CTPA vs. V/Q Scan

Radiation Dose Comparison

• CT Pulmonary Angiography (CTPA)
  • Delivers a higher radiation dose to the maternal chest (breast and lungs).
  • Approximate effective dose: 2?4 mSv, depending on technique and patient size.
  • Breast tissue in young women and pregnant patients is especially sensitive to radiation, making this a consideration.
• V/Q Scan
  • Delivers a lower radiation dose to the maternal chest but a slightly higher dose to the fetus compared to CTPA.
  • Approximate effective dose: 0.5?1.0 mSv to the maternal chest.
  • Fetal radiation dose: 0.1?0.3 mSv.

Why V/Q Scan is Preferred in Pregnancy

1. Lower Maternal Chest Dose
   • V/Q scan avoids significant breast radiation, making it safer for young women and pregnant patients concerned about radiation to breast tissue.
2. Clinical Context
   • In pregnant patients with normal chest X-ray findings, V/Q scans are more likely to yield interpretable results without unnecessary additional imaging.
3. Fetal Dose Consideration
   • While the fetal dose is slightly higher in V/Q scans compared to CTPA, the total dose remains within acceptable safety limits.
4. Avoiding Contrast Use
   • CTPA requires iodinated contrast, which may pose theoretical risks to the developing fetus, particularly to the thyroid.

This distinction highlights why the choice between CTPA and V/Q scan in pregnancy depends on individual risk factors, clinical presentation, and imaging availability. Would you like this integrated into the definition?

• • Acute PE Pulmonary Infarction