Journal for Vascular Ultrasound

To evaluate the role of duplex scanning as an imaging tool in surveillance of the natural history of femoropopliteal arterial segments treated with self-expandable nitinol stents.

From March 1999 to December 2001, 92 limbs in 84 patients were treated with self-expanding stents in the femoropopliteal (FP) segment for the relief of chronic limb ischemia. Follow-up studies included color duplex ultrasonography (CDU) and ankle/brachial indices (ABIs) in 57 limbs. Duplex criteria used to determine the presence of a significant in-stent stenosis was an increase in the peak systolic velocity within the stent of >100% from the proximal segment. The presence of a hemodynamically significant stenosis was then correlated with the concurrent ABI.

Eleven in-stent stenoses were documented in 11 limbs. In those patients, the mean decrease in ABI was 0.29, ranging from 0.13 to 0.50. In 46 patients with a <50% stenosis identified on CDU, the mean change in ABI was by comparison not significant.

From these data, the degree of in-stent stenosis (>50%) by duplex ultrasonographic criteria correlates well with a significant stenosis within a stented segment of the femoropopliteal artery. It seems that CDU is an ideal noninvasive imaging tool to objectively surveillance stent patency.

Color duplex ultrasound (CDU) is routinely used in the evaluation of aortic endografts in many centers. CDU compliments computed tomography (CT) and selective angiography in the identification of persistent endoleaks in these grafts. Because of the complexity of these procedures and the subtle nature of endoleaks, CDU can be time-consuming and challenging. Contrast agents can improve the ease of imaging by rapidly detecting low flow endoleaks. The application of ultrasound contrast agents has been studied in other specialties, such as cardiac echocardiography. This article describes our technique and early experience using contrast-enhanced CDU in aortic endograft assessment.

Nineteen patients being seen for a routine CDU examination after endovascular aortic aneurysm repair were evaluated according to published protocol. An initial CDU examination was completed, thoroughly assessing for the presence of graft patency, limb dysfunction, and endoleak. After patient consent, a focused ultrasound was performed using a Food and Drug Administration–approved contrast agent (Optison). The residual aneurysm sac was closely inspected after a 0.3-ml intravenous injection. A maximum of three injections were given in 10-min intervals, with careful evaluation in transverse and sagittal views of the residual aortic sac. Contrast was used to confirm endoleaks noted on the baseline study and help clarify subtle perigraft flow, especially on suboptimal examinations.

Of the 19 patients given the contrast agent, none had side effects, and all tolerated contrast well. In 9 of 19 examinations, contrast-enhanced CDU confirmed the baseline results positive for perigraft endoleak. Six of nine studies had improved ease of identification of endoleak with contrast. Six of 19 studies were negative for endoleak before and after contrast. Three of 19 studies were indeterminate for endoleak by CDU only secondary to bowel gas and body habitus. The contrast agent was given and was negative for endoleak in these three cases. One study was initially negative for endoleak by CDU, and contrast revealed a small lumber artery leaking into the aneurysm sac. The contrast was easily identified within the endograft and leak sites in all patients.

CDU is a valuable modality in the postoperative evaluation of endovascular aortic aneurysm repairs. These examinations can be challenging and subject to limitations including bowel gas and body habitus, even when performed by experienced technologists. Color artifacts within the residual aneurysm sac can be difficult to differentiate from true endoleak. Contrast-enhanced CDU can improve the technologist's confidence in the detection of endoleaks.

Traditionally, duplex ultrasonography has played a secondary role in the pre-operative assessment of lower extremity arterial bypass graft revision, being used more as a follow-up tool, with more expensive and invasive modalities being used primarily. This case demonstrates the accuracy and reliability of using duplex ultrasonography alone in the management of lower extremity bypass graft revision, as well as postoperative follow-up.

A 76-year-old man was seen in the diagnostic vascular unit for 2-week postoperative assessment after a left common femoral artery (CFA) aneurysm repair. Five months previously he had undergone right lower extremity femoral-to-posteriortibia in situ bypass graft for superficial femoral artery occlusion and a popliteal artery aneurysm. Ankle brachial indices were performed at his 2-week follow-up and showed a significant decrease in the right ankle brachial index (ABI) from 0.79 to 0.41. A right lower extremity duplex ultrasonography was performed and revealed significantly decreased flow velocities within the graft secondary to an arteriovenous fistula (AVF) found at the midthigh. The patient was scheduled for ligation of the AVF to restore adequate flow to the right lower extremity. The right thigh AV fistula was marked with duplex ultrasonography immediately before surgery. An incision was made directly over the marked AVF site, and the vein graft was isolated, revealing a large posterior medial AV fistula. Postoperative ABIs were significantly increased to 0.85 on the right side.

This case demonstrates the usefulness, accuracy, and reliability of duplex ultrasonography in the management of lower extremity arterial bypass grafts. All preoperative decisions were made on the basis of noninvasive vascular laboratory studies.

Circuits containing bypass grafts are made up of four elements: (1) the inflow tract, (2) the graft, (3) the collateral beds, and (4) the outflow tract. The fundamental principles developed by Poiseuille, Ohm, and Bernoulli can facilitate our understanding of the hemodynamics that occur within the arterial circuit containing bypass grafts.

A 59-year-old man was seen at our diagnostic vascular unit with severe claudication. Invasive and noninvasive vascular studies revealed occlusion of his aorta and bilateral common iliac arteries with reconstitution at bilateral groins by way of visceral vessels. Elective aortobifemoral bypass graft surgery was performed.

Postoperatively, duplex ultrasonography (Phillips/ATL 5000, Bothell, WA, 7-MHz linear array transducer) performed on bilateral groins revealed prograde flow distal to the anastomoses and retrograde flow involving the distal external iliac arteries proximal to the anastomoses.

Depending on the outflow resistance, flow might be prograde to the leg or retrograde to the pelvis and/or muscle proximal to the anastomosis or a combination of both as demonstrated in this case study. Such retrograde flow is desirable when one needs to perfuse the pelvis or thigh and not desirable if it steals blood from distal circulation.

The preceding fundamental principles refer to flow and pressure as inseparable manifestations of the total energetics of circulation. These principles are applied to the following case study and demonstrate competitive flow and pressure resistance relationships that exist within the arterial circuit containing a bypass graft.

Since 1991, treatment of cerebral saccular aneurysms with coils by means of an endovascular approach has become increasingly used as an alternative to surgery. After this procedure, thromboembolic complications of stroke and transient ischemic attack, as well as silent embolic events seen on MRI, have been reported. The detection of microemboli (MES) in the cerebral circulation in a variety of conditions has been well established and has been observed in asymptomatic and symptomatic patients. We present a case of a 41-year-old man with subarachnoid hemorrhage (SAH) from a vertebrobasilar junction aneurysm treated with Guglielmi detachable coils. Multiple MES were detected in the basilar artery during serial transcranial Power M-mode Doppler (PMD) studies. A battery of tests was done to establish the source of embolization from the coiled aneurysm.

By use of conventional techniques, diagnostic TCD studies to determine the presence of vasospasm were performed using a Neuroguard Neuroflow (Medasonics, Freemont, CA). PMD, a new technique for the detection of emboli, was then performed using Spencer Technologies TCD100M (Seattle, WA). The TCD100M is a digital Doppler and displays Doppler power as intensity in an M-mode format. PMD signals are further colored red or blue according, to direction. MES are seen as high-power tracks in the PMD image as described by Moehring et al (Ultrasound Med Biol. 2002;28:49–57).

Because of the possibility of multiple sources of embolization, our efforts were aimed at proving that the source of the embolization was the coiled aneurysm. Echocardiography, bubble studies, carotid duplex ultrasonography, and emboli monitoring of both middle cerebral and vertebral arteries did not show any MES. Power M-mode examination pointed to a depth of 85 mm in the basilar artery as the point where embolization began. This battery of tests strongly supports the presumptive origin and source of MES to be the coiled aneurysm of the vertebrobasilar junction.

Our case presentation demonstrates continuous silent microembolization from a previously coiled aneurysm. TCD has an important role in assessing patients with cerebral aneurysms for the detection of MES.