Imaging of Aortic Disease - Dr. Naveed Ahmad, MD

Key Concepts in Imaging of Aortic Disease

Modality of Choice: CT angiography (CTA) is the primary diagnostic test for acute aortic diseases due to 24-hour availability, rapid scanning speed, broad anatomic coverage from thoracic to abdominal aorta, and high spatial/temporal resolution.
ECG-Gating: Essential for evaluating the aortic root and ascending aorta to eliminate cardiac motion artifacts (which can mimic intimal flaps).
Normal Dimensions: Standard thoracic aortic diameters vary by age and sex; for example, the normal ascending aorta diameter is approximately 2.8 cm .
Aortic Dissection: Diagnosed by identifying an intimal flap separating true and false lumens. The false lumen typically arises along the outer curvature, and non-thrombosed false lumens strongly suggest acuity.
Intramural Hematoma (IMH): Accounts for roughly 10% of suspected dissections. Characterized by crescentic high-attenuation wall thickening on non-contrast CT without an identifiable intimal tear.
Penetrating Atherosclerotic Ulcer (PAU): Deep “button-shaped” ulcerations projecting beyond the expected intimal surface into the media, frequently leading to localized hematoma or pseudoaneurysm formation.
Coarctation: Well-visualized via CTA/MRA for anatomic narrowing, collateral vessel networks (e.g., internal mammary and intercostal arteries), and associated bicuspid aortic valves, though physiological gradients require functional testing.
Takayasu Arteritis: Characterized by concentric wall thickening and luminal stenosis. MRI/MRA or delayed contrast phases demonstrate active wall enhancement, and PET-CT highlights increased $18\text{F-FDG}$ metabolic uptake.
Traumatic Aortic Injury (TAI): Most commonly occurs at the aortic isthmus (proximal descending aorta) secondary to high-speed deceleration, presenting as a focal intimal disruption, contour irregularity, or localized pseudoaneurysm with mediastinal hemorrhage.
Post-Intervention Surveillance: Post-TEVAR or surgical repair imaging requires assessing graft integrity, tracking false lumen thrombosis, and actively ruling out perigraft fluid, air foci, or endoleaks.

Radiology Case Scenarios & Multiple-Choice Questions

Category 1: Aortic Dissection & Technical Artifacts

Case 1

A 65-year-old male undergoes a non-ECG-gated chest CT in the emergency department for acute chest pain. The axial images through the ascending aorta reveal a sharp, linear filling defect spanning across the vessel lumen that traverses tissue planes.

Question: What is the most appropriate next step or interpretation for this finding?
- A. Immediate surgical consultation for acute Type A aortic dissection.
- B. Recognize the finding as a streak artifact from high-density contrast in the superior vena cava and evaluate for a true intimal flap.
- C. Administer intravenous beta-blockers for a confirmed intramural hematoma.
- D. Schedule urgent catheter-based digital subtraction angiography.
Answer & Explanation: B. On non-ECG-gated scans, streak artifacts from dense contrast within the superior vena cava or brachiocephalic veins can project across the ascending aorta, mimicking an intimal flap. True intimal flaps are non-linear, follow anatomical contours, and do not cross tissue planes.

Category 2: Intramural Hematoma (IMH)

Case 2

A 58-year-old hypertensive female presents with severe tearing back pain. A non-contrast chest CT reveals a smooth, crescentic high-attenuation wall thickening of the descending thoracic aorta surrounding a displaced intimal calcification plaque. A repeat scan with IV contrast confirms the crescentic thickening without identifying an intimal tear or blood flow within the thickened wall.

Question: Which diagnosis best fits this imaging profile?
- A. Penetrating atherosclerotic ulcer
- B. Acute aortic dissection with a completely thrombosed false lumen
- C. Acute intramural hematoma (IMH)
- D. Mycotic aneurysm
Answer & Explanation: C. IMH is defined by crescentic wall thickening of high attenuation on pre-contrast CT scans without a patent communication or intimal tear between the true and false lumens. It represents hemorrhage into the media, often originating from vasa vasorum rupture.

Category 3: Penetrating Atherosclerotic Ulcer (PAU)

Case 3

A 77-year-old man with a history of severe peripheral vascular disease presents with recurrent embolic strokes. A dedicated chest CTA demonstrates a localized, deep, “button-shaped” outpouching of contrast material protruding through a calcified atherosclerotic plaque into the deep wall of the distal aortic arch, accompanied by overlying thrombus.

Question: What is the specific term for this focal lesion, which carries a risk of progression to rupture or intramural hematoma?
- A. Sinus of Valsalva aneurysm
- B. Penetrating atherosclerotic ulcer (PAU)
- C. Kommerell diverticulum
- D. Complicated type B dissection
Answer & Explanation: B. Penetrating atherosclerotic ulcers (PAUs) occur when an atherosclerotic plaque ulcerates and penetrates deep through the internal elastic lamina into the media, creating a focal crater that can lead to local bleeding, false lumen formation, or rupture.

Category 4: Aortic Aneurysms & Sinus of Valsalva

Case 4

A 40-year-old man presents with sudden-onset chest pain and signs of right heart failure. Cardiac CTA demonstrates a saccular aneurysm arising from the right coronary sinus of Valsalva that protrudes into and communicates directly with the right ventricular outflow tract, creating a left-to-right shunt.

Question: What is the most common embryologic or congenital origin of isolated sinus of Valsalva aneurysms, and which sinus is most frequently involved?
- A. Acquired syphilis; left coronary sinus
- B. Deficiency between the aortic media and annulus fibrosus; right coronary sinus
- C. Marfan syndromic medial necrosis; noncoronary sinus
- D. Bicuspid valve aortopathy; posterior sinus
Answer & Explanation: B. Sinus of Valsalva aneurysms typically stem from a congenital weakness or deficiency between the aortic media and the annulus fibrosus. They most commonly involve the right coronary sinus (followed by noncoronary and left), frequently rupturing into right-sided cardiac chambers.

Category 5: Coarctation of the Aorta

Case 5

A 27-year-old man undergoes a gated chest CTA to evaluate refractory hypertension. Multiplanar reformats demonstrate a discrete, shelf-like narrowing of the proximal descending thoracic aorta just distal to the left subclavian artery. Additionally, the scan shows markedly hypertrophied internal mammary and intercostal arteries serving as collaterals.

Question: On standard chest radiographs, which classic sign is frequently associated with the collateral vessel enlargement seen in this condition?
- A. “Figure-3” sign and rib notching
- B. Water-bottle heart configuration
- C. Fleischner sign
- D. Hampton hump
Answer & Explanation: A. Coarctation of the aorta classically features a “figure-3” sign (or inverse 3 sign on barium esophagograms/CT) on chest radiographs and posteroanterior views, alongside inferior rib notching (typically ribs 3 through 9) caused by dilated, pulsatile intercostal collateral arteries.

Category 6: Traumatic Aortic Injury (TAI)

Case 6

A 22-year-old driver involved in a high-speed motor vehicle collision undergoes emergency trauma CTA. Axial and sagittal “candy-cane” reconstructions of the thorax demonstrate a short, focal contour outpouching and intimal flap at the level of the aortic isthmus, surrounded by localized mediastinal hematoma.

Question: What is the most common anatomical location for acute traumatic aortic disruption secondary to rapid deceleration injuries?
- A. Ascending aorta above the sinotubular junction
- B. Aortic isthmus (proximal descending thoracic aorta)
- C. Mid-abdominal aorta near the renal arteries
- D. Transverse aortic arch between the carotid arteries
Answer & Explanation: B. The aortic isthmus (the junction between the fixed aortic arch and the mobile descending thoracic aorta) is subject to extreme shear forces during rapid deceleration, making it the most frequent site of traumatic aortic injury.

Category 7: Noninfectious Aortitis (Takayasu Arteritis)

Case 7

An 18-year-old female with systemic hypertension and constitutional symptoms undergoes evaluation for Takayasu arteritis. Contrast-enhanced CT angiography demonstrates smooth, circumferential soft tissue thickening of the aortic wall and severe luminal stenosis of the left common carotid and right renal arteries. An ${}^{18}\text{F-FDG}$ PET-CT is performed.

Question: What is the primary diagnostic utility of adding PET-CT or delayed MR imaging in this inflammatory arteriopathy?
- A. To accurately size endovascular stent-graft diameters
- B. To detect active metabolic inflammation and wall edema before irreversible fibrotic luminal narrowing occurs
- C. To definitively rule out bicuspid aortic valve morphology
- D. To measure instantaneous trans-stenotic pressure gradients
Answer & Explanation: B. In Takayasu arteritis, PET-CT and delayed-phase contrast MRI highlight increased metabolic activity and active mural inflammation within the thickened aortic wall, helping differentiate acute inflammatory stages from chronic, end-stage fibrosis.

Category 8: Postoperative Aorta & Complications

Case 8

A 50-year-old male who underwent ascending aortic replacement and TEVAR 3 weeks ago presents with low-grade fevers and abdominal discomfort. Follow-up CTA reveals an increase in low-attenuation fluid collections surrounding the graft, accompanied by newly developed small pockets of gas bubbles within the perigraft soft tissue stranding.

Question: What do the presence of expanding low-attenuation fluid and internal gas bubbles within the perigraft space strongly suggest in the early postoperative period?
- A. Normal expected postoperative inflammatory response resolving over time
- B. Type II endoleak from lumbar artery backflow
- C. An infected perigraft collection (graft infection)
- D. Uncomplicated perigraft seroma formation
Answer & Explanation: C. While mild low-attenuation fluid can represent a normal postsurgical inflammatory change early on, an increasing volume of fluid, worsening fat stranding, and especially the presence of gas bubbles weeks after surgery strongly raise the clinical and radiologic suspicion for an infected perigraft collection.

Category 9: Endovascular Aortic Repair (TEVAR) & Endoleaks

Case 9

A patient undergoes thoracic endovascular aortic repair (TEVAR) for a descending thoracic aortic aneurysm. A delayed-phase CT scan (acquired 90 seconds post-contrast injection) is performed as part of the follow-up protocol.

Question: Why are delayed scan images (1 to 2 minutes post-injection) explicitly required during follow-up CTA protocols after TEVAR?
- A. To measure the exact peak systolic pressure gradient across the stent graft
- B. To properly evaluate the coronary artery ostia without motion artifact
- C. To reliably depict slow venous or sac opacification from endoleaks and evaluate chronic false lumens
- D. To eliminate beam-hardening artifacts originating from the sternal wires
Answer & Explanation: C. Delayed-phase scans (1 to 2 minutes) allow sufficient time for contrast to pool or slowly track into endoleaks or residual patent false lumens, which might be missed on rapid arterial-phase acquisitions optimized solely for lumen opacification.

Category 10: Congenital Aortic Anomalies (Vascular Rings)

Case 10

A 32-year-old male presents with chronic progressive dysphagia (“dysphagia lusoria”). Gated chest CTA demonstrates a right-sided aortic arch with an aberrant left subclavian artery originating from a large posterior vascular pouch.

Question: What is the classic name of the diverticulum-like vascular outpouching from which the aberrant branch vessel typically originates in this anomaly?
- A. Diverticulum of Kommerell
- B. Sinus of Valsalva diverticulum
- C. Ductus bump
- D. Aortic root abscess
Answer & Explanation: A. The diverticulum of Kommerell represents a remnant of the embryonic dorsal aorta, appearing as a focal aneurysmal dilation at the origin of an aberrant subclavian artery (most commonly an aberrant left subclavian arising from a right-sided arch, or an aberrant right subclavian arising from a left-sided arch) that can compress the esophagus and trachea.