Fig. 37.1
(a) Angiogram reveals a normal course of the popliteal artery with a normal ankle pulse volume recording (inset) when the foot is in the neutral position. (b) With passive dorsiflexion of the foot, the popliteal artery becomes occluded, and the ankle pulse volume recording becomes flat (inset). (c) Computed tomographic angiography reveals popliteal artery occlusion due to popliteal artery entrapment syndrome. From Rutherford’s Vascular Surgery, 7th Ed., Volume 2, Cronenwett and Johnston (eds.), Saunders Elsevier, 2010:1731-2. Reprinted with permission
A combination of imaging examinations is required for an early and accurate diagnosis [86]. MRI and CT angiography can reveal a segmental stenosis or occlusion of the popliteal artery (Fig. 37.1c), which may lead to embolism of the small crural arteries. MRI imaging may demonstrate abnormal tendinous insertion, which originates from gastrocnemius medial head (Fig. 37.2), confirming the diagnosis of popliteal entrapment syndrome [85].
Fig. 37.2
Magnetic resonance imaging demonstrating abnormal tendinous insertion, which originates from gastrocnemius medial head. From Vascular and Endovascular Surgery: A Comprehensive Review, 8th Ed., W. Moore (ed), Elsevier Saunders, 2013:124. Reprinted with permission
Role of Vascular Lab in Penile Circulation
Impotence can be psychogenic, neuorogenic, hormonal, vascular, or drug related. Diabetes mellitus is often a factor in both neurogenic and vasculogenic impotence. Doppler evaluation in erectile dysfunction has a significant role in determining the cause of erectile dysfunction. The advantages of penile Doppler and pharmacologic duplex ultrasonography include objective, minimally invasive evaluation of penile hemodynamics at a relatively low cost. Various parameters, such as diameter of the cavernosal artery, peak systolic flow velocity, degree of arterial dilatation and acceleration time, have been suggested for the diagnosis of arteriogenic erectile dysfunction, but peak systolic flow velocity is the most accurate indicator of arterial disease [88]. Doppler penile pressure studies are helpful in identifying a possible vascular cause. Similarly, plethysmography has been used effectively to quantitate penile blood flow [89].
Doppler Technique
A pneumatic cuff measurin g 2.5 cm in width (2.5 × 12.5 cm or 2.5 × 9 cm) is applied to the base of the penis. A return of blood flow when the cuff is deflated can be detected by a mercury strain-gauge plethysmograph, a photoplethysmograph applied to the anterolateral aspect of the shaft, or a Doppler flow probe (Fig. 37.3). Although some investigators have positioned the probe over the dorsal penile arteries, others have emphasized the importance of detecting flow in the cavernosal artery. Because the penile blood supply is paired, an obstruction may occasionally be limited to only one side. It has been recommended that the pressures be measured on both sides of the penis [89]. In normal individuals under 40 years of age, the penile-brachial index (penile pressure divided by the brachial systolic pressure) was found to be 0.99 ± 1.15. Patients over the age of 40 years without symptoms of impotence tend to have lower indices. Penile-brachial indices >0.75–0.8 are considered compatible with normal erectile function; an index of <0.60 is diagnostic of vasculogenic impotence [90]. Knowledge of the penile pressure can be used to guide the surgeon in planning the operative approach to aneurysmal or obstructive occlusive disease of the aortoiliac segment. Maintenance of blood flow to the internal iliac artery will preserve potency and restoration of flow to this artery and will often improve penile pressure and erectile function.
Fig. 37.3
Method for measuring the penile Doppler pressures using a Doppler flow probe on the dorsal penile artery
However, Mahe et al. [91] found that a normal penile pressure cannot rule out the presence of lesions on the arteries supplying the hypogastric circulation in patients with arterial claudication. They evaluated the diagnostic accuracy of the penile brachial index (PBI) <0.60 to investigate arteriographic lesions on arteries supplying the hypogastric circulation in 88 male patients referred for Fontaine stage II. A ROC curve was used to define the diagnostic performance of the PBI and search for a specific cutoff point in this population. The accuracy for detecting an arterial stenosis or occlusion on at least one side was 69%). A PBI of ≤0.45 had a sensitivity of 74% and a specificity of 68% in discriminating the 19 patients with bilateral arterial occlusion from the other 66 patients. They concluded that the PBI is relatively insensitive for the detection of proximal abnormal blood flow impairment, except in cases of bilateral occlusion of the arteries supplying the hypogastric circulation in patients with claudication.
Inuzuka et al. [92] conducted a study to assess the pelvic circulation during endovascular abdominal aortic aneurysm repair (EVAR) with a new monitoring system measuring penile and buttock blood flow. They measured the PBI during EVAR by pulse-volume-plethysmography. They also measured bilateral gluteal tissue oxygen metabolism with near-infrared spectroscopy to provide a gluteal tissue oxygenation index. They studied 22 men who underwent aorto-uni-iliac stent graft with crossover bypass for exclusion of abdominal aortic aneurysms. Twelve patients underwent aorto-uni-common iliac artery stent graft and ten underwent aorto-uni-external iliac artery stent graft. They reported an immediate reduction in the PBI during the EVAR procedure in all patients. After revascularization of the ipsilateral limb of the stent graft, the recovery of the PBI was significantly less in the aorto-uni-external iliac artery stent graft group. After completion of the crossover bypass, the PBI returned to baseline values. There was a bilateral reduction in gluteal tissue oxygenation index during malperfusion of the internal iliac artery in both groups. After revascularization of the ipsilateral limb of the stent graft, the ipsilateral tissue oxygenation index returned to the baseline level in the aorto-uni-common iliac artery stent graft patients, but recovery was incomplete in the aorto-uni-external iliac artery stent graft patients. In contrast, the contralateral tissue oxygenation index remained low in both groups after revascularization of the ipsilateral limb of the stent graft. Only after completion of crossover bypass did the contralateral tissue oxygenation index recover to the baseline level in both groups. They concluded that both the tissue oxygenation index at the buttocks and the PBI are a sensitive reflection of pelvic hemodynamics. Penile blood flow and bilateral gluteal blood flow are supplied via different circulations and both should be monitored for full assessment of the pelvic circulation.
Duplex Imaging Techniques for Penile Circulation
Duplex imagings can be used to assess penile circulation as follows: the cavernous arteries are measured bilaterally in an A/P and transverse orientation. Color Doppler imaging is also a sensitive means of detecting cavernous artery blood flow , thus permitting more rapid identification of these vessels [93] (Figs. 37.4 and 37.5). The examiner measures the PSVs in the dorsal and cavernous arteries bilaterally (Figs. 37.6 and 37.7). This is followed by injections of specific medications, e.g., papaverine and/or prostaglandin by the urologist utilizing the lateral aspect of the proximal shaft of the penis (Fig. 37.8). Repeat velocity measurements are obtained post injection. These can be measured at 1 or 2 min after injection; multiple measurements may be obtained at various increments for up to 6 min after the injection. PSV and end-diastolic velocity measurements are obtained from the proximal cavernous arteries before full erection is achieved. This may require taking several measurements to obtain the highest velocity recording. The deep dorsal vein flow velocity is also measured from a dorsal approach, with light probe pressure. The dimensions of the cavernous arteries are also measured in the A/P and transverse views during systole. The examiner should observe the time elapsed since injection and document when velocities are recorded.
Fig. 37.4
Position of the scan head (duplex ultrasound) for examination of the cavernous artery . Notice the scan head is positioned on the ventral aspect of the penis
Fig. 37.5
Position of the scan head to show the dorsal penile artery . Notice the position of the scan head on the dorsal aspect of the penis
Fig. 37.6
A color duplex image of the cavernous artery . Please note the color flow as indicated by the arrow
Fig. 37.7
(a) A color duplex image of the cavernous artery (see arrow). The Doppler flow velocity spectrum with a peak systolic velocity of approximately 40 cm/s is shown at the bottom of the figure. (b) A color duplex image of the cavernous artery (see arrow). The Doppler flow velocity spectrum with a peak systolic velocity of approximately 15 cm/s is shown at the bottom of the figure
Fig. 37.8
An illustration of the structure of the penis with the position of the needle used for injection of vasodilators
It has been noted that PSVs generally increase after injection: a normal velocity is equal to or greater than 30 cm/s, 25–29 cm/s is a marginal value, and <25 cm/s is considered an abnormal velocity. To be noted, since the time when the highest PSV is reached after injection varies among individuals, it is imperative to obtain serial measurements. These velocities may occur 5, 10, 15, or 20 min after injection, with a nearly equal distribution. Post injection, the deep dorsal venous flow velocity should not increase with the following criteria to be followed: normal <3 cm/s, moderate increase 10–20 cm/s, and markedly increased >20 cm/s. It has been suggested that an increase to >4 cm/s may indicate a venous leak, which could contribute to the erectile dysfunction. The diameter of the cavernous arteries normally increases (dilates) after injection.
Measurement of PSVs in the cavernosal arteries after intracavernosal injection currently appears to be the best ultrasound approach for evaluating patients with suspected arteriogenic impotence [93, 94]. Several other studies recently reported on the value of color duplex ultrasonography in the diagnosis of vasculogenic erectile dysfunction [95–98]. Roy et al. [96] conducted a study to evaluate the role of duplex sonography for flaccid penis and the potential role in the evaluation of impotence. Forty-four men underwent duplex Doppler sonography with peak systolic measurements before and after intracavernous injection of prostaglandin E(1). Three different cutoff values for lowest normal PSV before injection—5, 10, and 15 cm/s were tested. Thirteen patients had arteriogenic insufficiency based on post intracavernous injection duplex sonography and clinical response. Results for different cutoff PSV values of 5, 10, and 15 cm/s in diagnosing arteriogenic impotence were sensitivity 29%, 96%, and 100%; specificity 100%, 92%, and 23%; negative predictive value 80%, 92%, and 100%; positive predictive value 100%, 81%, and 41%; and overall accuracy 79%, 93%, and 44%, respectively. In the flaccid state, there was a significant difference in mean PSV between the “normal” group (12.6 ± 0.9 cm/s) and the arteriogenic impotence group (7.7 ± 1.1 cm/s). Twenty-nine patients with a bilateral PSV of 10 cm/s or less before intracavernous injection had a normal clinical response. They concluded that a cutoff PSV value of 10 cm/s in the flaccid state had the best accuracy in predicting arterial insufficiency. Duplex Doppler sonography is proposed as the initial test to evaluate the penile arterial supply and to determine whether patients are good candidates for therapy with intracavernous injection.
Gontero et al. [99] conducted a study regarding the fact that an increased sympathetic tone may cause an equivocal response to a prostaglandin E1(PGE1) penile Doppler ultrasound examination interpreted as a venous leak. They evaluated the ultrasound parameters and erectile response to the addition of phentolamine to a PGE1 penile Doppler ultrasound examination to ascertain whether the addition of phentolamine would abolish a suboptimal response. This study included 32 patients who had either a clinical suspicion of venogenic impotence or a previous Doppler ultrasound pattern of venous leakage. These patients underwent a Doppler ultrasound after a total dose of 20 μg of PGE1. The peak systolic velocity (PSV), end-diastolic velocity (EDV), and grade of erection were documented. If erectile response was suboptimal, regardless of the EDV measurement, 2 mg of intracavernosal phentolamine was administered, and measurements were repeated. Six patients had a normal erectile response, and the remaining 26 received phentolamine. A significant increase in PSV between baseline and 20 μg PGE1 (p < 0.001) was observed in all cases. There was a significant increase in the grade of erection (p = 0.0001) and a significant reduction in the EDV (p = 0.0001) after phentolamine. They observed a reduction in the EDV to below 0.0 cm/s (−1) in 16 patients. Four patients with an EDV <5.0 cm/s (−1) but >0.0 cm/s (−1) had an improved erectile response following phentolamine, while six showed persistent EDV elevation >5 cm/s (−1). No priapism was documented. They felt that it is essential to ensure cavernosal relaxation using phentolamine before a Doppler ultrasound diagnosis of venous leak is made. This two-stage assessment will allow this to be done efficiently and with a low risk of priapism.
Upper Extremity Ischemia and Vasospastic Diseases
Upper extremity ischemia is relatively infrequent and can be caused by atherosclerosis, vasospasm, emboli, and trauma, which might be caused by diagnostic arterial catheterization. The segmental pressures and Doppler flow or PVRs can be measured at the level of the upper arm, forearm, and wrist, as well as in one or more digits to aid in diagnosing and localizing the obstructing lesion. Doppler ultrasound can accurately assess the patency of the palmar arch, which should be considered in all patients suspected of having intrinsic small vessel disease of the hand, or prior to cannulation of either the radial or the ulnar arteries. After catheterization, pressure data can be used to determine whether an accident has occurred. With spasm, the blood pressure drops only moderately and recovers rapidly.
Sumner and Strandness [100] described the characteristic peaked pulse seen in the digit volume pulse contours of patients with cold sensitivity secondary to collagen vascular disease or other forms of intrinsic digital artery disease. This is in contrast to patients with pure vasospasm where the contour is normal in configuration but of decreased amplitude. Figure 37.9 shows three typical digit pulse contours obtained with a mercury-in-Silastic plethysmograph. The normal pulse contour has a sharp systolic upswing that rises rapidly to a peak and then drops off rapidly toward the baseline. The downslope of this curve is bowed toward the baseline and usually contains a prominent dicrotic notch midway between the peak and baseline. In contrast, the pulse found distal to an arterial obstruction is considerably more rounded as seen in the obstructive contour. The upswing is delayed, the downslope is bowed away from the baseline, and there is no dicrotic notch. In several cases of arterial obstruction, no pulse is perceptible. The peaked pulse has a somewhat more delayed upswing than the normal pulse. Near the peak, there is an anacrotic notch. On the downslope, a dicrotic notch is present that is less prominent and located closer to the peak than normally seen.
Fig. 37.9
Digit pulse contours. From left to right: normal contour , obstructive contour, peaked contour
At room temperature, digital perfusion may be normal in persons with early vasospastic disease . To examine these patients, baseline PVRs of all digits are obtained. The hands are then immersed in iced water for 3 min or as long as tolerated. Serial digital PVRs are measured as rewarming occurs. If they fail to return to baseline levels within 5 min, a pathologic degree of vasospasm is likely. Measuring digit or toe pressure might also be helpful in distinguishing between primary vasospastic Raynaud’s disease and obstructive organic disease or Raynaud’s syndrome. In the primary disease, the digital pressure is almost normal, but in the obstructive disease, the digital pressure is markedly decreased. It should be noted that the toe pressure is normally a few millimeters of mercury less than the arm pressure and the finger pressure is a few millimeters higher than the arm pressure in young adults, but almost equal to the arm pressure in old patients. After the hands are immersed in iced water, the digital pressure in a normal individual will drop very slightly, but will return to normal very rapidly. In patients with primary vasospastic disease, the digital pressure will drop more significantly and might take a few minutes or more to come back. The digital pressure in organic obstructive disease will drop very dramatically (from 60 to 0 mmHg) and will take longer to return to normal. Further details of upper extremity vascular evaluation will be described in Chap. 30.
Arteriovenous Malformations
Arteriovenous malformations (AVMs) or fistulas can be congenital or acquired (e.g., traumatic). They consist of an abnormal connection between a high-pressure arterial system and a low-pressure venous system, causing marked hemodynamic and anatomic changes. AVMs may involve proximal and distal arteries and veins as well as collateral arteries and veins. Its diameter and length predict the resistance it offers. If the fistula is proximal in its location (close to the heart), the potential for cardiac complications, primarily cardiac failure, increases. This is in contrast to peripheral fistulas, which are less likely to cause congestive heart failure, but more likely to cause limb ischemia. Generally, flow in the artery proximal to the fistula is greatly increased, especially during diastole, because the fistula markedly reduces resistance, and this is in contrast to what is seen in a normal artery. The proximal venous flow is also increased and becomes more pulsatile in character. The blood pressure distal to the fistula is somewhat reduced. The direction of the blood flow, on the other hand, is normal if the fistula resistance exceeds that of the distal vascular bed. If the fistula is chronic and large, arterial blood flow may be retrograde. A long-standing chronic fistula tends to elevate venous pressure, and blood flow is retrograde in the distal vein, which is associated with an incompetent valve.
Diagnosis of AVM may be evident on physical examination by (1) the presence of a characteristic bruit, (2) the presence of secondary varicosities and cutaneous changes of chronic venous insufficiency, (3) the obliteration of the thrill producing bradycardiac response, or (4) the association of a birthmark and limb overgrowth in patients with congenital AVM. However, such combinations are often lacking. Szilagyi et al. [101] reported in one of the largest series of AVMs that the classic triad of birthmark, varicosities, and limb enlargement was present in only 30% of patients, with various other combinations of signs present in 38% and 32% of those presenting with only a single physical finding. Various noninvasive diagnostic tests have been used for the diagnosis of extremity AV fistula including (1) Doppler segmental limb systolic pressure determination, (2) segmental limb plethysmography or PVRs, and (3) analysis of arterial velocity waveforms.
The reduced peripheral resistance associated with AVM decreases the mean arterial pressure proximally, but increases the pulse pressure [102]. Accordingly, proximal to the malformation, segmental systolic pressures are usually increased compared with the contralateral normal extremity. Beyond the malformation, they are normal, except in the case of stealing from distal arterial flow, when they may be decreased. The decreased peripheral resistance eliminates the reverse flow, which is seen in the normal Doppler analog wave tracing and increases the forward flow, particularly during diastole. Consequently, the end-diastolic velocity waveforms are elevated above the zero baseline in direct proportion to the decrease in peripheral resistance. However, this pattern can be seen in cases of reactive hyperemia, after vasodilator drugs, in warming of the extremity, in inflammation, and after sympathectomy. In the absence of these conditions, it is diagnostic of AVM.
The PVR can also be helpful in the diagnosis of these malformations. The AVM increases the segmental limb volume changes normally produced by pulsatile arterial flow and can be detected with the PVR. The PVRs proximal to the fistula are uniformly increased. The anacrotic slope and peak are sharper with loss of the dicrotic wave. Distal to the fistula, the PVRs are often entirely normal. The same principles can be applied in evaluating patients with angioaccess for kidney failure, premature atypical varicose veins, unequal limb growth, or hemangiomas of the extremity.
Labeled microsphere methods can be used to estimate the AV shunt flow of an extremity. The percentage of total extremity flow that passes through AVMs may be measured by comparing the relative levels of pulmonary radioactivity following an arterial and then a peripheral venous injection of a radionuclide-labeled human albumin microsphere [103]. These methods may be used to confirm or exclude the diagnosis of AVM, particularly if the results of the noninvasive vascular tests are equivocal. They also provide a quantitative estimate of the AV shunt flow, which may be helpful in determining its prognosis and the need for any therapeutic interventions. Patients with congenital AVM may also present primarily as venous pathology, e.g., varicose veins. Some of these may harbor AVM and have secondary venous insufficiency, whereas others may have a venous anomaly, but no AVM (e.g., Klippel-Trenaunay or Parkes Weber syndrome). These can be investigated by various venous noninvasive studies that will be described later. Various venous abnormalities can be detected, including deep venous valvular insufficiency, which can be diagnosed by simple Doppler ultrasound or venous duplex imaging or PPG.
In spite of the role of various noninvasive vascular tests described earlier, other testing may be necessary in many patients with AVM of the extremities to achieve sufficient information on which to base major clinical decisions. Magnetic resonance imaging, which is preferable to contrasted enhanced CT, might be necessary in evaluating congenital vascular malformation [103]. Magnetic resonance imaging gives a better definition of the anatomic extent and the feasibility of surgical resection than CT and allows multiplanar views (Fig. 37.10). This subject is described in more detail in Chap. 34.
Fig. 37.10
Magnetic resonance imaging of the lower extremity showing a vascular mass with high flow changes in the anterior medial compartment of the thigh region (involving the vastus medialis muscle) as noted in the upper portion of this transverse view
Hemodialysis Access Graft Imaging
Duplex scanning of hemodialysis access grafts documents abnormalities and abnormal velocity or volume flow measurements commonly associated with a graft malfunction. Imaging of these grafts is indicated in the following circumstances: elevated venous pressure, difficult needle placement, loss of graft thrill, swelling around the graft site, perigraft mass, recirculation, abnormal laboratory values, and underdeveloped Cimino fistula.
Technique
No specific preparation is required prior to the examination. The patient may sit or lie in the supine position and clothing may need to be removed, depending on the location of the access graft. The extremity is inspected for raised or flattened areas of edema or discoloration of the hand or digits. The presence of a pulse is abnormal and the presence of a palpable thrill is a normal finding. Brachial pressures should be obtained and should be equal bilaterally. A five to ten MHz linear transducer can be used, and the graft should be examined in both transverse and longitudinal scan planes. Both the inflow artery, the entire length of the graft, and the outflow veins should be imaged. Velocities or volume flow measurements must be done at the anastomotic sites, mid graft, puncture sites, and sites of obvious lumen reduction. If color flow imaging is available, observe the image for frequency increases, turbulence, and flow channel changes. The following can be some of the limitations of this technique: excessive swelling, infection, anatomic variations, uncooperative patients, and visualization of the graft less than 48 h after placement. The technician or examiner should be familiar with the type of hemodialysis access graft to facilitate mapping . Figure 37.11 is an example of these grafts.
Fig. 37.11
Illustration showing various AV grafts. As noticed in this figure, these grafts can be autogenous (radial artery to cephalic vein) or synthetic (Gore-Tex graft between the brachial artery and the antecubital vein or between the brachial artery and the distal axillary or proximal brachial veins)
Interpretations
As indicated earlier, the following should be identified and documented as to location, extent, and type, aneurysmal changes (including pseudoaneurysms), puncture sites for hematomas or leaks, thrombus, and perigraft fluid collection.
PSVs vary according to the graft type and normally can be quite elevated. Presently, there are no standardized velocity criteria for hemodialysis access grafts. It is generally recommended to have follow-up studies, which will provide specific comparisons to previous studies. A low PSV obtained throughout the graft could suggest an arterial inflow dysfunction. It is generally believed that the venous anastomosis and outflow veins are the most common sites of stenosis in these grafts, which can be caused by an increased arterial pressure introduced through the vein and/or intima hyperplasia. Occasionally, steal syndrome can be observed whereby the distal arterial blood flow is reversed into the venous circulation of the lower systems. This can be manifested by pain on exertion of the affected extremity as well as pallor and coolness of the skin distal to the shunt.
Table 37.1 summarizes a generally agreed upon interpretation criteria that are adapted from an Advanced Technology Laboratory manual.
Table 37.1
Dialysis access graft imaging: interpretation criteria
Classification | Velocity (cm/s)* | Image characteristics | |
|---|---|---|---|
Normal | Mid graft | Anastomotic sites | No visible narrowing |
>150 cm/s | >300 cm/s | Distended outflow veins | |
Aneurysms, puncture sites, perigraft fluid may be visible | |||
Moderate stenosis | Mid graft | Anastomotic sites | Decrease in lumen diameter |
100–150 cm/s | >300 cm/s at stenosis | Echogenic narrowing | |
Wall abnormalities | |||
Severe stenosis | Mid graft | Intraluminal echogenicity | |
<100 cm/s | <2 mm lumen | ||
>50% diameter reduction | |||
Marked velocity acceleration | |||
Marked reduction in lumen diameter with color Doppler
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