A 58-year-old man with a remote history of treated syphilis dies of heart failure. Autopsy shows an aneurysm of the ascending aorta with a wrinkled, 'tree-bark' intimal appearance. The abdominal aorta below the renal arteries is entirely normal. Why is the infrarenal segment spared?
- A It has a thicker adventitia
- B Treponema pallidum cannot survive at core body temperature in that region
- C The ascending aorta has abundant vasa vasorum while the infrarenal abdominal aorta has few or none ✓
- D Blood flow velocity is highest in the ascending aorta
Correct answer: C. The ascending aorta has abundant vasa vasorum while the infrarenal abdominal aorta has few or none
Explanation
Syphilitic aortitis involves the ascending aorta because T. pallidum reaches the media through the vasa vasorum, which are numerous there and sparse or absent in the abdominal aorta below the renal arteries. The resulting obliterative endarteritis of vasa vasorum causes medial ischemia, elastic fiber destruction, and scarring that produces the tree-bark intima and aneurysm. This vascular anatomy explains the classic sparing of the infrarenal segment.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.