What does a mild basal anterolateral defect on a Positron Emission Tomography (PET) scan indicate?

Interpretation of Mild Basal Anterolateral Defect on PET Scan

A mild basal anterolateral defect on a PET scan most likely represents a perfusion abnormality that could indicate early coronary artery disease affecting the left circumflex artery territory, which requires further clinical correlation and potential follow-up testing.

Understanding Myocardial Perfusion Defects on PET Imaging

Types of Defects and Their Significance

• PET myocardial perfusion imaging can detect both fixed and reversible perfusion defects, with fixed defects typically representing infarction and reversible defects indicating ischemia 1
• Even mild perfusion defects in the inferolateral wall (similar anatomical region to basal anterolateral) should be carefully managed, especially in high-risk patients, as they may indicate significant coronary artery disease 2
• Mild defects may represent early disease that has not yet progressed to cause visible perfusion defects on conventional imaging 3

Clinical Implications of Basal Anterolateral Defects

• The basal anterolateral region is typically supplied by the left circumflex artery (LCX), and defects in this area may indicate stenosis in this vessel 2
• Studies have shown that approximately 52.7% of patients with mild inferolateral wall ischemia on myocardial perfusion imaging had stenosis in the LCX territory when evaluated with coronary angiography 2
• Reduced myocardial blood flow reserve (MBFR) in specific territories suggests potential disease in the coronary arteries that may not be visible on conventional angiography 3

Diagnostic Considerations

Potential Causes of Defects

• True coronary artery disease affecting the left circumflex artery territory 2
• Microvascular dysfunction, especially common in women 3
• Attenuation artifacts due to misregistration between attenuation and emission images (a common cause of false-positive defects in PET imaging) 4
• Non-coronary causes such as cardiac fibromas or other intramural masses (uncommon but possible) 5

Avoiding Misinterpretation

• Misregistration between attenuation and emission images occurs in approximately 21.4% of PET perfusion studies and can cause artifactual defects 4
• Risk factors for misregistration artifacts include higher body mass index, larger heart size, and diaphragmatic displacement 4
• Careful quality control and potentially manual realignment of attenuation and emission images may be necessary to avoid false-positive interpretations 4

Management Approach

Initial Assessment

• Correlate the PET finding with clinical symptoms (presence/absence of angina) and cardiac risk factors 3
• Review the quantitative myocardial blood flow reserve (MBFR) values if available, as normal MBFR is generally considered to be ≥2.0, while values <2.0 suggest impaired coronary flow reserve 3

Further Evaluation Options

• If the patient has significant symptoms or high-risk features, consider invasive coronary angiography to evaluate for obstructive coronary artery disease 3
• For intermediate lesions identified on angiography, fractional flow reserve (FFR) assessment may provide additional functional information 3
• In patients with suspected obstructive CAD, a sequential approach using coronary CT angiography followed by selective functional perfusion imaging has shown good prognostic value 6

Treatment Considerations

• Optimize guideline-directed medical therapy for patients with mild reductions in myocardial blood flow reserve 3
• For patients with confirmed significant stenosis, revascularization may be considered 2
• Studies have shown that approximately 21.9% of patients with mild perfusion defects underwent revascularization during one-year follow-up 2

Special Considerations

Hybrid Imaging Advantages

• Combined PET-CT imaging provides both anatomical evaluation of coronary arteries and corresponding functional status, offering complementary information in a single scanning session 7
• This approach may help guide clinical management in patients with suspected coronary artery disease 7

Risk Stratification

• Patients with normal perfusion on PET have excellent outcomes comparable to those without obstructive CAD on coronary CTA 6
• Patients with abnormal perfusion have significantly higher rates of adverse events (approximately 5 times higher) compared to those with normal perfusion 6

Remember that even mild perfusion defects should not be dismissed, particularly in patients with risk factors for coronary artery disease, as they may represent early disease requiring preventive interventions or further evaluation 2.