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What is Investigation of choice for diagnosis of pulmonary embolism? and explain in detail?
Ans. b (CT Scan Chest). (Ref. Harrison's principles of Medicine, 18th/Ch. 262)PULMONARY EMBOLISM -CXR - SIGNS :'Hampton's hump'A peripheral area of more or less wedge-shaped consolidation may indicate associated infarction.Westermark signRegional oligaema with sharp cut-off of a pulmonary embolism may be seen.Palla's signEnlarged right descending pulmonary artery.CTA:# Computed tomography of the chest with intravenous contrast (CECT) is the principal imaging test for the diagnosis of PE.# Studies have shown that CTPA has a very high sensitivity and specificity with a high negative predictive value for the detection of pulmonary embolism.# Multidetector-row spiral CT acquires all chest images with <1 mm resolution during a short breath hold. This generation of CT scanners can image small peripheral emboli.# Sixth-order branches can be seen with resolution superior to conventional invasive pulmonary angiography.# In patients with PE, RV enlargement on chest CT indicates a fivefold increased likelihood of death within the next 30 days compared with PE patients with normal RV size on chest CT.Radioisotope scan:# Lung scanning is now a second-line diagnostic test for PE and used for who cannot tolerate IV contrast.# Small particulate aggregates of albumin labelled with a gamma-emitting radionuclide are injected intravenously and are trapped in the pulmonary capillary bed.# The perfusion scan defect indicates absent or decreased blood flow, possibly due to PE.# Ventilation scans with radiolabeled gases (xenon or krypton), improve the specificity of the perfusion scan.# A normal perfusion scan virtually excludes PE because a pulmonary embolus presents as V/Q mismatch.Magnetic Resonance (MR) (Contrast-Enhanced):# When ultrasound is equivocal, MR venography is an excellent imaging modality to diagnose DVT.# MR utilizes gadolinium, which, unlike iodinated contrast used in venography or CTA, is not nephrotoxic.# MR should be considered for suspected DVT or PE patients with renal insufficiency or contrast dye allergy.# MRA detects large proximal PE but is not reliable for smaller segmental and subsegmental PE.Pulmonary angiography:# Chest CT with contrast has virtually replaced invasive pulmonary angiography as a diagnostic test. Although pulmonary angiography is supposed to be the definitive and gold standard means of diagnosing PE, there are only few indications for it, which includes:- Embolectomy is the therapeutic option- Specific diagnosis necessary for proper management- Indeterminate V/Q scan with high clinical suspicion & risky anticoagulant therapy.Tests for pulmonary embolismCommentD-dimer assay- Screening test of choiceContrast enhanced spiral (multislice) CT - Investigation of choice/ Best/ Preferred testPulmonary (conventional/catheter) arteriography- Gold standard or definitive test/Test for evaluationVQ scan (ventilation perfusion scan)- Second line investigation2-D ECHO (unreliable test)- McConnell's signX-ray- 'Hampton's hump', Westermark sign, Palla's sign