The popliteal artery, an unusual muscular artery with wall properties similar to the aorta: implications for susceptibility to aneurysm formation?

Endovascular treatment of popliteal artery aneurysms

Popliteal artery aneurysms are relatively uncommon but potentially limb-threatening lesions that can thrombose or cause distal embolization. Identification of these aneurysms, especially in patients with abdominal aortic aneurysms, is imperative, and prophylactic treatment with either surgical exclusion and bypass or endoluminal stent grafting is critical to prevent these poor outcomes. Endovascular approaches currently using the Viabahn stent graft offer several advantages, including a minimally invasive approach, fewer perioperative complications, and a faster recovery. This must be balanced with a potentially higher failure rate or requirement for reintervention, although contemporary series report comparable short-term outcomes. We present our approach to the evaluation and diagnosis of popliteal aneurysms, the technical aspects of endovascular popliteal aneurysm repair, and a representative case study.

A Contemporary Review of Popliteal Artery Aneurysms

Popliteal artery aneurysms account for 85% of all peripheral aneurysms and are frequently associated with abdominal aortic aneurysms. Up to 75% of all popliteal artery aneurysms are discovered in symptomatic patients who present with arterial insufficiency, leg swelling, or pain. Popliteal artery aneurysms can be diagnosed with duplex ultrasonography. Aneurysm repair should be considered for all symptomatic patients with rest pain or limb-threatening symptoms. Asymptomatic aneurysms larger than 2 cm should also be treated to prevent the development of limb-threatening ischemia and assure better surgical bypass graft patency and longer freedom from amputation. Conventional aneurysm repair consists of either opening the aneurysm sac and interposing a bypass graft or aneurysm ligation combined with bypass grafting. If the aneurysm sac is left intact, side branch perfusion may persist and the aneurysm may continue to enlarge and can rupture. Endovascular popliteal aneurysm repair has not demonstrated clinical equipoise to standard surgery but may be advantageous in select high-risk patients.

Evidence for reduced sympatholysis in leg resistance vasculature of healthy older women

Inhibition of a sympathetic stimulus (i.e., sympatholysis) during forearm exercise is reduced with age in women. This age-related alteration has not been characterized in the lower extremity vasculature of women, and the potential for blunting of the conduit artery dilatory response to a sudden increase in shear stress [flow-mediated dilation (FMD)] has not been examined in older adults of either sex. In the present study, we assessed popliteal artery diameter and velocity (Doppler ultrasound) in 16 young (23 +/- 1 yr) and 14 older (69 +/- 1 yr) women after 5 min of distal calf occlusion (FMD), 3 min of hand immersion in ice water [cold pressor test (CPT)], and 5 min of distal calf occlusion combined with hand immersion in ice water (FMD+CPT). Peak popliteal conductance after 5-min ischemia was not significantly different in young vs. older women. During the combined stimulus (FMD+CPT), the magnitude of vasoconstriction in the calf (reduction in peak popliteal artery conductance) was similar (5-8%), despite reduced resting adrenergic sensitivity to CPT [young (Y): -27.3 +/- 3.8%; older (O): -15.8 +/- 2.2%; P < 0.05] and blunted muscle sympathetic nerve activity responses to CPT (Y: 12.7 +/- 3.6 bursts/min; O: 7.8 +/- 2.5 bursts/min; P < 0.05) in older women. Popliteal FMD, normalized to the shear stimulus, was attenuated by 60-70% in older women. Peak popliteal diameter, measured during the combined stimulus (FMD+CPT), was blunted in young but not in older women (Y FMD: 5.5 +/- 0.1 mm; Y FMD+CPT: 5.4 +/- 0.1 mm; P = 0.03; O FMD: 5.8 +/- 0.2 mm; O FMD+CPT: 5.8 +/- 0.2 mm). These results confirm previous findings of diminished reactivity in the conduit arteries of older humans and provide the first evidence of reduced sympatholysis in the leg resistance vasculature of older women.

Size of normal and aneurysmal popliteal arteries: A duplex ultrasound study

OBJECTIVE

To define diameter at three levels along the popliteal artery and its relation to the inflow arteries in the normal state and in popliteal aneurysms.

METHODS

The external diameter of the arteries was determined by duplex ultrasound scanning at the common femoral (CFA), superficial femoral artery (SFA), proximal popliteal artery (PPOP), mid-popliteal artery (MPOP), and distal popliteal artery (DPOP). Examinations were performed in 104 healthy men and 100 women. In addition, patients were screened for the presence of popliteal aneurysms (diameter >10 mm). Findings in healthy male subjects were compared with those with popliteal aneurysms.

RESULTS

Mean arterial diameters in normal men were larger than in women, but the SFA/CFA ratio was smaller in women (0.74 +/- 0.08 vs 0.78 +/- 0.09; P < .001) and the MPOP/SFA ratio was larger (0.98 +/- 0.11 vs 0.94 +/- 0.12; P = .001). In both genders, normal popliteal artery diameter was not uniform throughout its length, with PPOP and MPOP being nearly identical, and DPOP was smaller. MPOP diameter correlated most closely with SFA diameter (r = 0.51; P < .001) and less with height, weight and body surface area (r = 0.2 to 0.3) and was not associated with age or the presence of hypertension. In 27 men with 45 patent, fusiform popliteal aneurysms (10 to 44 mm) the site of maximal dilatation was in the region of the MPOP in 39 cases and near the PPOP in only 6 cases. The DPOP was never the largest segment and only in one case was it >10 mm. Arterial diameter in aneurysm patients was larger than normal at all levels but was greatest near the MPOP level (15.7 +/- 6.9). Popliteal-to-SFA diameter ratios were increased in the aneurysm group at all three levels but were greatest at the MPOP level (1.85 vs 0.94, P < .001). Comparing 15 popliteal aneurysms >20 mm with smaller ones, distal popliteal artery changed to the least extent but did increase in diameter (6.1 +/- 1.2 vs 7.0 +/- 1.4, P < .04). In larger aneurysms the MPOP/SFA ratio increased from 1.54 to 2.5 (P < .001).

CONCLUSION

The diameter of the normal popliteal artery is not uniform throughout its length. In popliteal aneurysms, the region of the MPOP is most commonly the largest diameter. The MPOP/SFA ratio is greater than normal in popliteal aneurysms and increases in larger aneurysms. DPOP does dilate but to a lesser extent then PPOP and MPOP, making endovascular repair anatomically feasible in most popliteal aneurysms.

Impaired vascular growth in late adolescence after intrauterine growth restriction

BACKGROUND

Abnormal blood flow in a fetus small for gestational age indicates true fetal intrauterine growth restriction (IUGR). We tested the hypothesis that IUGR with abnormal fetal blood flow is associated with long-term abnormal vascular morphology and function in adolescence.

METHODS AND RESULTS

In a prospective study, vascular mechanical properties of the common carotid artery (CCA), abdominal aorta, and popliteal artery (PA) were assessed by echo-tracking sonography in 21 adolescents with IUGR and abnormal fetal aortic blood flow and in 23 adolescents with normal fetal growth and normal fetal aortic blood flow. Endothelium-dependent and -independent vasodilatation of the brachial artery was measured by high-resolution ultrasound. After adjustment for body surface area and sex, the IUGR group had significantly smaller end-diastolic vessel diameters than the referents in the abdominal aorta and PA (mean difference, 1.7 mm [95% CI, 0.62 to 2.74] and 0.6 mm [95% CI, 0.25 to 1.02], respectively) (P=0.003 and P=0.002, respectively), with a similar trend in the CCA (P=0.09). A higher resting heart rate was observed in the IUGR group (P=0.01). No differences were found in stiffness or in endothelium-dependent and -independent vasodilatation between the 2 groups.

CONCLUSIONS

IUGR caused by placental insufficiency appears to be associated with impaired vascular growth persisting into young adulthood in both men and women. The smaller aortic dimensions and the higher resting heart rate seen in adolescents with previous IUGR may be of importance for future cardiovascular health.