Cross-sectional pattern of collateral vessels in patients with superficial femoral artery occlusion

Collateral artery pathways of the femoral and popliteal artery

BACKGROUND

The role of collateral artery circulation in the lower limb is under debate but clinically relevant, particularly when using covered stents for occlusive disease. Covered stents seem to outperform nitinol stents in extensive disease, but collaterals could be essential in case of acute thrombosis. In the present study, we describe the collateral pathways of the deep and superficial femoral artery (DFA, SFA) and the popliteal artery (PA), observed in human cadavers.

METHODS

Ten fresh frozen cadaver legs were selected. The SFA and DFA were separately cannulated and injected with a different colored latex mixture simultaneously. After curing of the latex, the circulation was dissected thus visualizing the main arteries and their collateral vessels. The process was photographed and recorded, and collateral pathways were analyzed using a standardized vessel segmentation. The upper leg was divided in three regions, that is, the femoral triangle (F), the adductor canal (H), and the popliteal fossa (P) that, in turn, were split in three segments (1, 2, and 3, from proximal to distal).

RESULTS

Overall, 113 collateral vessels were found; 69 originated from the DFA, 34 from the SFA, and 10 from the PA. The majority of collaterals originating from the DFA terminated in the SFA (57%). Fifty-six of 113 collaterals (50%) ended in either the distal adductor channel (H3) or the proximal PA (P1). Another 28 collateral arteries (25%) had their origin in this segment (H3, P1) and mostly connected to the P2 and P3 segments. Forty-three collaterals of the DFA and H3 segment had a direct or indirect connection to below the knee muscles.

CONCLUSIONS

The majority of collaterals originate from the DFA, and the greater part of all collaterals has a connection with the H3-P1 segment. This observation may have clinical implications in the planning of endovascular procedures.

Magnetic resonance imaging in peripheral arterial disease: reproducibility of the assessment of morphological and functional vascular status

OBJECTIVES

The aim of the current study was to test the reproducibility of different quantitative magnetic resonance imaging (MRI) methods to assess the morphologic and functional peripheral vascular status and vascular adaptations over time in patients with peripheral arterial disease (PAD).

MATERIALS AND METHODS

Ten patients with proven PAD (intermittent claudication) and arterial collateral formation within the upper leg and 10 healthy volunteers were included. All subjects underwent 2 identical MR examinations of the lower extremities on a clinical 1.5-T MR system, with a time interval of at least 3 days. The MR protocol consisted of 3D contrast-enhanced MR angiography to quantify the number of arteries and artery diameters of the upper leg, 2D cine MR phase contrast angiography flow measurements in the popliteal artery, dynamic contrast-enhanced (DCE) perfusion imaging to determine the influx constant and area under the curve, and dynamic blood oxygen level-dependent (BOLD) imaging in calf muscle to measure maximal relative T2* changes and time-to-peak. Data were analyzed by 2 independent MRI readers. Interscan and inter-reader reproducibility were determined as outcome measures and expressed as the coefficient of variation (CV).

RESULTS

Quantification of the number of arteries, artery diameter, and blood flow proved highly reproducible in patients (CV = 2.6%, 4.5%, and 15.8% at interscan level and 9.0%, 8.2%, and 7.0% at interreader level, respectively). Reproducibility of DCE and BOLD MRI was poor in patients with a CV up to 50.9%.

CONCLUSIONS

Quantification of the morphologic vascular status by contrast-enhanced MR angiography, as well as phase contrast angiography MRI to assess macrovascular blood flow proved highly reproducible in both PAD patients and healthy volunteers and might therefore be helpful in studying the development of collateral arteries in PAD patients and in unraveling the mechanisms underlying this process. Functional assessment of the microvascular status using DCE and BOLD, MRI did not prove reproducible at 1.5 T and is therefore currently not suitable for (clinical) application in PAD.

MR angiography of collateral arteries in a hind limb ischemia model: comparison between blood pool agent Gadomer and small contrast agent Gd-DTPA

The objective of this study was to compare the blood pool agent Gadomer with a small contrast agent for the visualization of ultra-small, collateral arteries (diameter<1 mm) with high resolution steady-state MR angiography (SS-MRA) in a rabbit hind limb ischemia model. Ten rabbits underwent unilateral femoral artery ligation. On days 14 and 21, high resolution SS-MRA (voxel size 0.49×0.49×0.50 mm³) was performed on a 3 Tesla clinical system after administration of either Gadomer (dose: 0.10 mmol/kg) or a small contrast agent (gadopentetate dimeglumine (Gd-DTPA), dose: 0.20 mmol/kg). All animals received both contrast agents on separate days. Selective intra-arterial x-ray angiograms (XRAs) were obtained in the ligated limb as a reference. The number of collaterals was counted by two independent observers. Image quality was evaluated with the contrast-to-noise ratio (CNR) in the femoral artery and collateral arteries. CNR for Gadomer was higher in both the femoral artery (Gadomer: 73±5 (mean ± SE); Gd-DTPA: 40±3; p<0.01) and collateral arteries (Gadomer: 18±4; Gd-DTPA: 9±1; p = 0.04). Neither day of acquisition nor contrast agent used influenced the number of identified collateral arteries (p = 0.30 and p = 0.14, respectively). An average of 4.5±1.0 (day 14, mean ± SD) and 5.3±1.2 (day 21) collaterals was found, which was comparable to XRA (5.6±1.7, averaged over days 14 and 21; p>0.10). Inter-observer variation was 24% and 18% for Gadomer and Gd-DTPA, respectively. In conclusion, blood pool agent Gadomer improved vessel conspicuity compared to Gd-DTPA. Steady-state MRA can be considered as an excellent non-invasive alternative to intra-arterial XRA for the visualization of ultra-small collateral arteries.

Dynamic contrast-enhanced MRI of muscle perfusion combined with MR angiography of collateral artery growth in a femoral artery ligation model

To assess the use of MRI for evaluating changes in muscle blood flow and number of collateral arteries, serial dynamic contrast-enhanced MRI (DCE-MRI) was combined with high-spatial-resolution contrast-enhanced MR angiography (MRA) in a peripheral ischemia model. The combined MRI (DCE-MRI and MRA) protocol was performed serially in 15 male rabbits at 2 h (day 0(+)), 7 days, and 21 days after femoral artery ligation. In the anterior tibial and soleus muscle, changes in resting muscle blood flow determined as the endothelial transfer coefficient (K(trans)) and arterial inflow delay from DCE-MRI and changes in the number of sub-millimeter sized collateral arteries as scored with MRA were measured. Directly after ligation, K(trans) in the anterior tibial muscle was reduced to 23% of that in the control limb, then recovered to 81% on day 7, and to 85 % on day 21. K(trans) in the soleus muscle recovered from a reduction to 63% on day 0(+), to 85% on day 7, and to 90% on day 21. The number of collaterals around the ligated femoral artery increased from 1.1 on day 0(+) to 4.2 on day 7, and 6.0 on day 21 in the ligated limb only. Combined DCE-MRI and MRA allows non-invasive serial monitoring of changes in muscle blood flow and growth of sub-millimeter sized collateral arteries in a rabbit femoral artery ligation model.

Magnetic resonance angiography reveals therapeutic enlargement of collateral vessels induced by VEGF in a murine model of peripheral arterial disease

PURPOSE

To quantify spontaneous and therapeutic arteriogenesis in vivo in a murine model of peripheral arterial disease using magnetic resonance angiography.

MATERIALS AND METHODS

Male, 8-12-week-old, C57/BL6 mice underwent femoral artery ligation; 21 days later, 2 mg/kg recombinant murine VEGF165, formulated for slow release, was injected into the ipsilateral gastrocnemius. The spontaneous (following ligation) and therapeutic (following vascular endothelial growth factor (VEGF)) formation of collateral vessels was quantified using 3D magnetic resonance angiography on a small-bore 4.7T system. Therapeutically induced angiogenesis and blood flow were quantified using an in situ anti-platelet endothelial cell adhesion molecule (PECAM) 1 radioimmunoassay and radiolabeled microsphere deposition, respectively.

RESULTS

Spontaneous arteriogenesis was visible in all animals five days after ligation. VEGF treatment doubled the arteriogenic response five days after treatment compared to vehicle (cross-sectional area of vessels: 0.96 vs. 0.46 mm2, P<0.01). VEGF also induced angiogenesis (PECAM1 levels 191% of vehicle, P<0.05) and increased blood flow specific to the injection site (57 vs. 7 mL/minute/100 g, P<0.05).

CONCLUSION

The presented methodology allowed in vivo quantification of spontaneous arteriogenesis in a murine model of peripheral arterial disease and demonstrated that therapeutic enlargement of collateral vessels is possible with VEGF.

Risk factors for poor collateral development in claudication

The objective of this retrospective, cross-sectional study was to determine risk factors for poor collateral development in patients with claudication. The authors listed all patients with calf claudication who had undergone angiography in this hospital between 1999 and 2001 and extracted those with superficial femoral artery (SFA) occlusion, a popliteal artery without major lesions, and at least 1 patent calf artery. Forty-five patients met the criteria, and concomitant disease and claudication characteristics, ankle/brachial index (ABI) and number of outflow vessels were recorded. Three blinded observers calculated the number of collaterals on the angiograms, and the collateral count was related to the other factors by use of regression analysis. The mean patient age was 69 years (SD 11), and 62% were women. Their walking distance was 90 m (77) and ABI 0.47 (0.15). Thirty-three percent had diabetes and 50% had duration of symptoms longer than 5 years. The mean number of collaterals bypassing the occlusion was 15.1 (SD 4.8). Univariate regression analysis indicated an association (p <0.08) between few collateral vessels and diabetes, short duration of symptoms, current smoking habits, and old age. In the multivariate analysis only diabetes and short duration of symptoms were related to having few collaterals. In patients with claudication and SFA occlusion, few collaterals from the deep femoral artery appear to be associated with having diabetes and a short duration of symptoms.