Popliteal artery aneurysms differ from abdominal aortic aneurysms in cellular topography and inflammatory markers

Objective: Popliteal artery aneurysms (PAAs) and abdominal aortic aneurysms (AAAs) frequently coincide; however, symptoms differ. We systematically assessed aneurysm cellular wall composition and inflammatory markers to compare both anatomic locations. Methods: Aneurysmal walls of 38 PAAs and 198 AAAs were harvested from patients undergoing elective open surgical repair. Elastin, collagen, smooth muscle cells, iron, and inflammatory cells were quantified by immunohistochemistry. In addition, protease and cytokine levels were measured. Results: Aneurysmal degradation resulted in similarly degraded media. The location of inflammation differed: the focus for T and B lymphocytes and plasma cells was the intima in PAAs (all P <.001) and the adventitia for AAAs (all P <.001). Iron was more often observed in PAAs than in AAAs (68% vs 1%; P <.001), indicating more previous intramural hemorrhages. Matrix metalloproteinase 2 activity was higher in PAAs than in AAAs (median [interquartile range], 0.363 [0.174-0.556] vs 0.187 [0.100-0.391]; P =.008), whereas matrix metalloproteinase 9 showed no difference. Walls of AAAs were richer in tested cytokine levels than were walls of PAAs. Conclusions: PAAs showed more signs of previous intramural hemorrhages compared with AAAs. In addition, inflammation in PAAs is mainly located in the intima, whereas its focus in AAAs is the adventitia. These results suggest important differences in the pathophysiologic mechanism of aneurysm formation between these locations and might explain the differences in presentation on diagnosis.