Increased wall stress of saccular versus fusiform aneurysms of the descending thoracic aorta.
BACKGROUND
Repair of fusiform descending thoracic aortic aneurysms (DTAs) is indicated when aneurysmal diameter exceeds a certain threshold; however, diameter-related indications for repair of saccular DTA are less well established.


METHODS
Human subjects with fusiform (n = 17) and saccular (n = 17) DTAs who underwent computed tomographic angiography were identified. Patients with aneurysms related to connective tissue disease were excluded. The thoracic aorta was segmented, reconstructed, and triangulated to create a mesh. Finite element analysis was performed using a pressure load of 120 mm Hg and a uniform aortic wall thickness of 3.2 mm to compare the pressure-induced wall stress of fusiform and saccular DTAs.


RESULTS
The mean maximum diameter of the fusiform DTAs (6.0 ± 1.5 cm) was significantly greater (p = 0.006) than that of the saccular DTAs (4.4 ± 1.8 cm). However, mean peak wall stress of the fusiform DTAs (0.33 ± 0.15 MPa) was equivalent to that of the saccular DTAs (0.30 ± 0.14 MPa), as found by using an equivalence threshold of 0.15 MPa. The mean normalized wall stress (peak wall stress divided by maximum aneurysm radius) of the saccular DTAs was greater than that of the fusiform DTAs (0.16 ± 0.09 MPa/cm vs. 0.11 ± 0.03 MPa/cm, p = 0.035).


CONCLUSIONS
The normalized wall stress for saccular DTA is greater than that for fusiform DTA, indicating that geometric factors such as aneurysm shape influence wall stress. These results suggest that saccular aneurysms may be more prone to rupture than fusiform aneurysms of similar diameter, provide a theoretical rationale for the repair of saccular DTAs at a smaller diameter, and suggest investigation of the role of biomechanical modeling in surgical decision making is warranted.
Department of General Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA 19104, USA.
Derek P
DP
Nathan
Chun
C
Xu
Alison M
AM
Pouch
Krishnan B
KB
Chandran
Benoit
B
Desjardins
Joseph H
JH
Gorman
Ron M
RM
Fairman
Robert C
RC
Gorman
Benjamin M
BM
Jackson
D000368:Aged; D000369:Aged, 80 and over; D001013:Aorta, Thoracic / Q000000981:diagnostic imaging / Q000503:physiopathology*; D017545:Aortic Aneurysm, Thoracic / Q000000981:diagnostic imaging / Q000503:physiopathology*; D001027:Aortography / Q000379:methods; D001696:Biomechanical Phenomena; D001794:Blood Pressure; D016009:Chi-Square Distribution; D003198:Computer Simulation; D005260:Female; D020342:Finite Element Analysis; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D015143:Philadelphia; D011379:Prognosis; D012189:Retrospective Studies; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed