What are the odds of subaortic stenosis (Subvalvular Aortic Stenosis) and Interrupted Aortic Arch (IAA) being false positives?

False Positive Rates in Subaortic Stenosis and Interrupted Aortic Arch Diagnosis

The false positive rate for subaortic stenosis (SAS) and interrupted aortic arch (IAA) is very low when appropriate imaging modalities are used, with CT angiography and MRI having specificities approaching 95-100%.

Diagnostic Accuracy of Imaging Modalities

Different imaging techniques have varying levels of accuracy for diagnosing aortic abnormalities:

CT Angiography (CTA)

• Specificity: >95% 1
• Gold standard for diagnosing aortic pathologies
• Provides excellent visualization of both the aortic arch and subaortic region
• Can detect associated anomalies that commonly occur with IAA

MRI

• Specificity: approaching 100% 1
• Excellent for detailed anatomical assessment
• Limited by longer acquisition time and reduced availability in emergency settings

Transesophageal Echocardiography (TEE)

• Specificity: 89% 1
• High sensitivity (99%) but more prone to false positives than CT or MRI
• Particularly useful for assessing subaortic stenosis severity

Transthoracic Echocardiography (TTE)

• Specificity: 93-96% for aortic dissection 2
• Lower sensitivity (59-85%) for aortic pathologies
• May miss subtle findings in the aortic arch
• More operator-dependent than CT or MRI

Potential Sources of False Positives

1. Technical limitations:

   • Reverberation artifacts in echocardiography can result in false-positive diagnosis 2
   • Patient positioning during CT can create pseudostenotic appearances

2. Anatomical variations:

   • Normal variants may be misinterpreted as pathological
   • Previous scarring or severe myxomatous changes can be indistinguishable from active pathology 2

3. Imaging quality issues:

   • Poor acoustic windows in echocardiography
   • Motion artifacts in CT or MRI
   • Inadequate contrast timing

Minimizing False Positives

To reduce the risk of false positive diagnoses:

1. Use multiple imaging modalities when diagnosis is uncertain:

   • If initial imaging suggests SAS or IAA but clinical suspicion is low, confirm with a second imaging modality 2
   • CT angiography should include non-contrast images to improve diagnostic accuracy 1

2. Ensure proper technique:

   • For echocardiography: exploit high frame rates to improve temporal resolution 2
   • For CT: extend imaging from thoracic inlet to pelvis for complete assessment 1

3. Experienced interpretation:

   • Images should be reviewed by specialists with expertise in congenital heart disease
   • Correlation with clinical findings is essential

Clinical Context

The clinical significance of false positives in SAS and IAA is substantial:

• IAA is a rare but critical congenital anomaly that typically presents in infancy with cardiac failure or shock 3
• SAS commonly coexists with IAA (13 out of 50 infants in one study) 4
• Misdiagnosis can lead to inappropriate management decisions, including unnecessary surgical intervention
• Conversely, missing these diagnoses can be fatal, particularly in neonates 5

Conclusion

When using appropriate imaging techniques and experienced interpretation, the false positive rate for subaortic stenosis and interrupted aortic arch is very low. CT angiography and MRI provide the highest specificity (>95%), making them the preferred diagnostic modalities when available. For definitive diagnosis, correlation of imaging findings with clinical presentation remains essential.