A Systematic Histopathologic Evaluation of Type-A Aortic Dissections Implies a Uniform Multiple-Hit Causation.

Area of Science:

• Cardiovascular Pathology
• Aortic Diseases
• Histopathology

Background:

• The underlying pathophysiology of acute type A aortic dissection (TAAD) remains poorly understood.
• Investigating vessel wall defects is crucial for understanding TAAD.
• Systematic study of aortic specimens from TAAD patients was conducted.

Purpose of the Study:

• To systematically evaluate vessel wall defects in acute type A aortic dissection (TAAD).
• To identify histopathological differences between TAAD specimens and control tissues.
• To elucidate the pathophysiologic basis of TAAD.

Main Methods:

• Histopathological analysis of ascending aortic wall specimens from 58 TAAD patients.
• Comparison with 17 autopsy-obtained control aortic specimens.
• Systematic evaluation of medial and intimal layers.

Main Results:

• TAAD specimens exhibited significant elastic fiber fragmentation, thinning, degeneration, and medial degeneration.
• Mucoid extracellular matrix accumulation and smooth muscle cell nuclei loss were prevalent in TAAD.
• The dissection plane correlated with the vasa vasorum network, and the intimal layer was significantly thinner in TAAD patients.

Conclusions:

• TAAD is associated with diffuse, pre-existing medial defects in the ascending aorta.
• A hypothesis of a developmental defect underlying TAAD is proposed.
• TAAD progression is attributed to a triple-hit mechanism involving intimal tear, diseased media, and vasa vasorum propagation.