Imaging

Toxic Lung Injury

Preliminary Diagnosis: Toxic lung injury (Silo-Filler's disease)

I. What imaging technique is first-line for this diagnosis

  • Chest radiographs (CXR) with posteroanterior (PA) and lateral projections

II. Describe the advantages and disadvantages of this technique for diagnosis of toxic lung injury (Silo-Filler's disease).

Advantages

  • Diagnostic for the noncardiogenic edema seen with toxic lung injury (TLI)

  • Exposes the patient to less ionizing radiation than computed tomography (CT) of the chest

  • Serial chest radiographs are sufficient to follow the course of TLI

Disadvantages

  • Initial CXR can be negative as the noncardiogenic edema of TLI appears anytime from immediately to 48 hours after injury (usually by 6 hours)

  • Less sensitive for other types of thoracic disease, such as associated trauma

III. What are the contraindications for the first-line imaging technique?

  • CXR has no significant contraindication

IV. What alternative imaging techniques are available?

  • High resolution CT (HRCT) chest without contrast

  • CT chest with intravenous contrast

  • CT chest without contrast

  • Ventilation perfusion (V/Q) scan

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of toxic lung injury (Silo-Filler's disease).

High resolution CT chest without contrast

Advantages

  • Diagnostic of TLI

  • Best alternative study in the scenario of unexplained chronic dyspnea and non-diagnostic chest radiography

  • Most capable study for diagnosis of any diffuse lung disease (i.e., hypersensitivity pneumonitis, interstitial lung disease, etc.)

  • HRCT with inspiratory and expiratory images can document air trapping, sometimes present in TLI

Disadvantages

  • HRCT performed without contrast is non-diagnostic for pulmonary thromboembolism (PTE)

  • More expensive and time-consuming, and exposes the patient to more ionizing radiation than chest radiography

CT chest with intravenous contrast

Advantages

  • Diagnostic of TLI

  • Best alternative study if there is also concern for traumatic thoracic injury

  • Appropriate alternative if infection or malignancy are other diagnostic considerations

Disadvantages

  • The contrast dose administered may have to be reduced or withheld if the patient has decreased renal function

  • Patients with known allergic reaction to iodinated contrast must undergo pre-treatment with steroids and anti-histamines for at least 13 hours prior to contrast dose, or have contrast withheld

  • Exposes the patient to ionizing radiation

CT chest without contrast

Advantages

  • Diagnostic of TLI

  • Can show other thoracic disease processes, including traumatic injury

Disadvantages

  • Exposes the patient to ionizing radiation

Ventilation perfusion (V/Q) scan

Advantages

  • V/Q scan can show air trapping or delayed radiotracer washout typical of TLI, even in the setting of negative CXR

  • V/Q scan can be diagnostic of PTE

Disadvantages

  • Less readily available and more time-consuming than CXR or CT

  • Exposes the patient to ionizing radiation

VI. What are the contraindications for the alternative imaging techniques?

High resolution CT chest without contrast

  • Patients unable to remain motionless and hold their breath for up to 25 seconds during the test will have images degraded by motion artifact

  • Contraindicated in pregnant women, especially in the first and second trimesters

CT chest with intravenous contrast

  • The contrast dose administered may have to be reduced or withheld if the patient has decreased renal function

  • Patients with known allergic reaction to iodinated contrast must undergo pre-treatment with steroids and anti-histamines for at least 13 hours prior to contrast dose, or have contrast withheld

  • Contraindicated in pregnant women, especially in the first and second trimesters

CT chest without contrast

  • Contraindicated in pregnant women, especially in the first and second trimesters

Ventilation perfusion (V/Q) scan

  • V/Q scan has no absolute contraindication

  • V/Q scan is not recommended for patients for whom there is high suspicion of massive PTE

  • Relative contraindications of V/Q scan include severe asthma, COPD, or cystic fibrosis

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