MRA tops ultrasound in lower limb bypass follow-up

MR angiography should be employed much earlier in the postoperative follow-up of severely ill patients with complex revascularization of cruropedal circulation, according to a German researcher during a Saturday scientific session at the European Congress of Radiology.

"MRA is superior to duplex ultrasound in cases of threatening bypass failure," said Dr. Oliver A. Meissner, a radiologist at Ludwig-Maximilian University in Munich. "MRA should be included in routine follow-up of patients undergoing cruropedal bypass surgery."

Meissner and colleagues evaluated 24 patients with 26 bypass grafts. MRA studies were obtained at three stations from the aorta to the midfoot. Degree of stenosis was compared with ultrasound and digital subtraction angiography in cases of discrepancy.

For analysis, the researchers divided each affected limb into five vascular segments: inflow arteries, proximal anastomosis, the graft, distal anastomosis, and outflow arteries.

The qualitative criteria were inadequate (image quality not sufficient enough to give a treatment option), intermediate, and excellent (easily possible to give a treatment therapy option).

The stenosis grading scale had four levels:
· less than 50%
· between 51% and 74%
· greater than 75%
· complete occlusion

MRA image quality was rated excellent or intermediate in 119/130 vascular segments (91.5%). The 11 segments graded as inadequate were mainly due to artifacts from bolus timing and patient movement.

Researchers encountered venous overlay in 17/26 lower leg segments. In two of these cases, evaluation of the outflow region was not feasible.

In 94/109 vascular segments (87%), MRA and ultrasound showed concordant findings. In eight discordant cases, ultrasound overlooked three high-grade stenoses, which were correctly identified by MRA and resulted in treatment.

In no case did MRA miss an area of stenosis of sufficient severity to require treatment. Additionally, there was good correlation between the findings of DSA and MRA (n = 8, r = 0.90).

"MRA is equal and in cases of complex revascularization even superior to duplex ultrasound in detecting failed grafts, and in the very small number of patients, we had a high agreement with DSA," Meissner said.

The researchers want to validate these results with more study and evaluate the cost-effectiveness of MRA in this patient population.