Makindo Medical Notes

Related Subjects: |Assessing Breathlessness |Pulmonary Embolism |Deep Vein Thrombosis |DVT/PE in pregnancy |CTPA

📖 Introduction

• CT Pulmonary Angiogram (CTPA) is the gold standard test to confirm or exclude pulmonary embolism (PE) in suspected cases (after Wells / Geneva score risk stratification).
• Typical diagnostic pathway: Wells score → D-dimer (if low/intermediate risk) → CTPA (if high risk or D-dimer positive).
• Uses rapid IV iodinated contrast injection → should fully opacify pulmonary arteries.
• PE = filling defect: contrast fails to fill the lumen, seen as a darker intraluminal area ± vessel cut-off.
• CTPA may also reveal alternative diagnoses (pneumonia, malignancy, pleural effusion, pneumothorax, aortic dissection).

🧭 Systematic Approach: How to Read a CTPA

1. ✅ Check contrast timing: are pulmonary arteries bright and well-opacified? If not, artefact or false negatives are likely.
2. ✅ Follow the arteries: start centrally (main → right & left pulmonary arteries → lobar → segmental → subsegmental branches).
3. ✅ Look for filling defects: sharply demarcated darker areas within contrast = thrombus. – Central clot: seen surrounded by contrast (“polo mint sign” on axial, “railway track sign” on sagittal/coronal). – Eccentric wall-adherent clot: partially obstructs lumen.
4. ✅ Check lung parenchyma (lung window): infarcts appear wedge-shaped, pleural-based opacities. Don’t miss pneumonia or masses.
5. ✅ Assess right heart strain: RV/LV ratio >1, septal flattening, reflux of contrast into IVC/hepatic veins → poor prognosis.
6. ✅ Review mediastinum & pleura: aortic dissection, lymphadenopathy, effusions.
7. ✅ Final sweep: scroll from lung apices to bases to avoid missed peripheral clots.

🫁 Pulmonary Artery Anatomy

• Main pulmonary artery bifurcates into: – Right pulmonary artery (RPA): horizontal, to right lung. – Left pulmonary artery (LPA): posterior, to left lung.
• Normal CTPA = uniform contrast filling throughout arterial tree.

⚠️ Contraindications

• 🤰 Pregnancy: radiation + contrast (consider V/Q if CXR normal).
• 💧 Renal impairment: risk of contrast nephropathy → check eGFR.
• ⚠️ Contrast allergy: avoid in severe iodine allergy; options = V/Q scan or MR angiography. Premedicate in mild allergy.

🩻 CTPA Images

📌 Practical Pitfalls

• ⏱️ Poor opacification: wrong contrast bolus timing → non-diagnostic study.
• 💨 Motion artefact: poor breath-holding may mimic PE (“pseudo-defect”).
• 📍 Subsegmental PEs: small, peripheral; clinical significance debated → always correlate with symptoms & discuss with respiratory/radiology team.
• 🧩 Non-thrombotic mimics: tumour emboli, fat emboli, artefacts → need correlation.

💡 Teaching Pearls

1️⃣ Always confirm contrast quality before interpreting.
2️⃣ Central → lobar → segmental → subsegmental search pattern.
3️⃣ Look for RV strain: prognostic marker.
4️⃣ Never forget to review lung windows and mediastinum → pneumonia, cancer, or dissection may explain the presentation.
5️⃣ If CTPA is negative but suspicion remains high → consider repeat CTPA, V/Q, or leg Doppler (for DVT).

🎥 Online Learning

• Part 1: How to Read a CTPA
• Part 2: How to Read a CTPA