Is a CT scan of the chest and aorta medically necessary for a patient with a new dilation of the ascending aorta and abdominal aortic aneurysm (AAA), given their complex medical history including paroxysmal atrial fibrillation, hypertension, obstructive sleep apnea, and chronic obstructive pulmonary disease (COPD)/asthma overlap?

CT Chest and Aorta with Contrast is Medically Necessary and Should Be Approved

For this patient with newly identified ascending aortic dilation on transthoracic echocardiography (TTE) and known abdominal aortic aneurysm (AAA), CT angiography (CTA) of the chest and aorta with intravenous contrast is the appropriate and medically necessary imaging study to confirm measurements, assess the entire aorta, and guide management decisions. 1, 2

Why CTA is the Standard of Care

Limitations of TTE for Ascending Aortic Assessment

• TTE has significant limitations in evaluating the aortic arch and proximal descending aorta, making it inadequate as the sole imaging modality for newly detected ascending aortic dilation 3
• When thoracic aortic dilatation is identified on TTE, the 2024 European Society of Cardiology guidelines explicitly recommend CTA or cardiac MRI to confirm TTE measurements, rule out aortic asymmetry, and determine baseline diameters for follow-up 3
• TTE is specifically not recommended for surveillance of aneurysms in the distal ascending aorta, aortic arch, or descending thoracic aorta 3

CTA as the Reference Standard

• The American College of Radiology designates CTA with intravenous contrast as the preferred imaging modality for thoracic aortic aneurysm, providing near 100% sensitivity and 98% specificity for detecting thoracic aortic pathology 1, 2
• CTA provides critical information about the aortic lumen, wall thickness, and surrounding structures that cannot be obtained from non-contrast studies 3, 2
• The 3D dataset from CTA allows for precise measurements perpendicular to the flow lumen, which is essential for accurate assessment and longitudinal follow-up 3, 1

Comprehensive Aortic Assessment Required

• When an aortic aneurysm is identified at any location (in this case, both ascending aorta and AAA), the 2024 ESC guidelines mandate assessment of the entire aorta at baseline and during follow-up 3
• Up to 27% of patients with AAA also have thoracic aneurysms, making comprehensive imaging essential 4
• This patient requires evaluation from the aortic root through the abdominal aorta to characterize both the ascending aortic dilation and the known AAA 3

Technical Protocol Specifications

Contrast Enhancement is Essential

• Contrast enhancement is mandatory because it allows visualization of the aortic lumen, assessment of wall thickness, detection of intraluminal thrombus, and identification of complications such as dissection or penetrating ulcers 3, 2
• Non-contrast CT significantly underestimates aortic pathology and cannot adequately assess the vessel lumen 3
• CTA was 95% sensitive and 100% specific for diagnosing Takayasu arteritis, demonstrating its superiority for vascular wall assessment 3

ECG-Gating for Ascending Aorta

• ECG-gated CTA is particularly important for the ascending aorta and aortic root to minimize cardiac motion artifacts that can simulate dissection or lead to inaccurate measurements 3, 1, 2
• ECG gating allows accurate orthogonal measurements and can provide information about aortic valve morphology and function 3, 1

Coverage Requirements

• The scan should extend from above the aortic arch through at least the aortoiliac bifurcation to evaluate the entire thoracic and abdominal aorta 3
• This coverage is necessary to assess both the ascending aortic dilation and the AAA in a single examination 3

Clinical Decision-Making Based on CTA Findings

Ascending Aortic Dilation Thresholds

• An ascending aortic diameter ≥40 mm is considered dilated and requires baseline documentation 3, 5
• Aneurysm is defined as approximately 5.0 cm for the ascending aorta (150% of normal) 3
• Surgery is recommended when ascending aortic diameter reaches ≥55 mm in patients with tricuspid aortic valve 3

AAA Management Thresholds

• Elective AAA repair is recommended when diameter reaches ≥55 mm in men or ≥50 mm in women 3, 4
• Surveillance intervals for AAA depend on size: every 6 months for 50-55 mm in men or 45-50 mm in women 3

Cardiovascular Risk Assessment

• Patients with aortic aneurysms have a 10-year risk of death from cardiovascular causes that is up to 15 times higher than the risk of aorta-related death 4
• This patient's comorbidities (atrial fibrillation, hypertension, COPD) place her at elevated cardiovascular risk, making comprehensive aortic assessment even more critical 4

Common Pitfalls to Avoid

Do Not Order Non-Contrast CT

• Non-contrast CT chest is inadequate for suspected aortic root dilation and will require repeat imaging with contrast, exposing the patient to unnecessary radiation 1
• Non-contrast CT cannot assess the aortic lumen or detect intraluminal thrombus, dissection, or penetrating ulcers 3, 2

Ensure Proper Measurement Technique

• Measurements must be made perpendicular to the long axis of the aorta using multiplanar reconstructions to avoid overestimation in tortuous vessels 4, 2
• Outer-to-outer wall measurements should be used for standardized evaluation 2

Alternative for Contrast Contraindications

• If this patient has severe renal insufficiency or contrast allergy, cardiac MRI/MRA is the appropriate alternative with comparable accuracy to CTA 1, 2
• Non-contrast MRA sequences can provide excellent aortic visualization without gadolinium 1

Addressing the Lung Transplant Mention

The authorization request mentions pseudoaneurysm or vascular complications after lung transplant, but the clinical history does not indicate this patient has had a lung transplant. This appears to be a documentation error or template language. Regardless, CTA remains the appropriate study for evaluating any suspected thoracic aortic pathology, including pseudoaneurysm 3, 2.

Coverage Decision Justification

This CTA examination meets medical necessity criteria because:

• TTE has identified new ascending aortic dilation requiring confirmatory cross-sectional imaging per guideline recommendations 3, 1
• The patient has known AAA requiring comprehensive aortic assessment 3, 4
• CTA is the reference standard for aortic aneurysm diagnosis and management planning 1, 2, 6
• The study will establish baseline measurements for future surveillance and determine if intervention thresholds have been reached 3
• Failure to obtain this imaging could result in missed surgical indications or progression to life-threatening complications such as dissection or rupture 3, 7