Chapter 7. Vascular Interventional Radiology^*

Interventional uroradiologic procedures can be divided into two major groups: vascular and percutaneous nonvascular. Percutaneous nonvascular interventional procedures are discussed elsewhere. The intravascular route is used, as the therapy of choice, for the embolization of arteriovenous fistulas (AVFs) or malformations, and for bleeding sites. Transcatheter embolization is used for tumor embolization, for the ablation of renal function, for the treatment of testicular vein and ovarian vein varices, and for the treatment of high-flow priapism (Ginat et al, 2009). Balloon angioplasty and stenting of stenotic renal arteries are frequently performed endovascular techniques for the treatment of ischemic nephropathy and secondary hypertension. Renal artery aneurysms may also be treated using catheter-directed techniques such as stent grafting and selective embolization. Occasionally, fibrinolytic agents are delivered via an endovascular catheter to thrombosed renal arteries. Mechanical devices are also available for endovascular treatment of thrombosed renal vessels. This chapter will review these intravascular interventions.

*The authors wish to thank Dr. Anthony Verstandig, Hadassah University Hospital, Jerusalem, Israel, for providing the clinical information and images of the patient depicted in Figures 7–4A and 7–4B.

Renal AVFs and Malformations

Transcatheter embolization is the treatment of choice for renal AVFs, which may be congenital, spontaneous, or acquired. Iatrogenic AVFs are the type most commonly treated by transcatheter embolization. These occur as a complication of such procedures as percutaneous renal biopsy (Libicher et al, 2006), nephrostomy placement, and pyelolithotomy. Trauma or surgery can also result in AVFs. AVF occurring in the transplant kidney is successfully managed by embolization. The classical angiographic finding of spontaneous or acquired AVF is a feeding artery with an early draining vein. Ancillary findings include pseudoaneurysm and extravasation of contrast material. Congenital AVMs (AV malformations) consist of a group of multiple coiled communicating vessels that may be associated with enlarged feeding arteries and draining veins.

The modes of clinical presentation include hematuria; retroperitoneal or intraperitoneal hemorrhage; and congestive heart failure, cardiomegaly, or both. Hypertension can occur as a consequence of ischemia secondary to venous shunting of blood away from the affected area. A bruit may be heard on physical examination. Duplex Doppler ultrasound is the most useful diagnostic study, performed before angiographic intervention.

Successful intervention requires the angiographic identification, selective catheterization, and embolization of the feeding artery (Figures 7–1A, B). Using a transfemoral approach, an abdominal aortogram is performed to identify the arterial supply to the bleeding kidney. In the case of a renal transplant, an initial pelvic angiogram is performed in a steep oblique projection. The artery supplying the bleeding site is selectively catheterized. A 3 French (3F) coaxial microcatheter is then used for subselective catheterization and embolization of the feeding artery. The use of a microcatheter allows accurate placement of the embolic material. Microcoils are used for the occlusion of iatrogenic AVFs because they can be deployed very precisely, thereby minimizing the loss of renal parenchyma due to resultant ischemia (Figures 7–2A through C). The procedure is usually performed without significant complications. Very rarely, inadvertent nontarget embolization or thrombosis of the renal artery can occur.

Bleeding Sites

Transcatheter embolization plays a key role in the management of hemorrhage in the urinary tract originating in the kidney, ureter, bladder, and pelvis (Ginat et al, 2009). Acute life-threatening hemorrhage can occur as a consequence of trauma, instrumentation, and tumors. Chronic intractable hemorrhage is associated with radiation cystitis, tumors, prostatectomy, and infiltrative disorders. Hemodynamically stable patients undergo a noninvasive diagnostic study such as contrast-enhanced computed tomography (CT), before embolization.

Pelvic fractures resulting in life-threatening hemorrhage require embolization for control if resuscitation and external pelvic fixation have been ineffective. Embolization has been shown to be very effective at arresting hemorrhage. Using a transfemoral approach, the practitioner performs a nonselective pelvic arteriogram before selective catheterization and embolization of the hypogastric arteries. Because of contralateral crossover blood supply, pelvic lesions are treated by bilateral embolization. Gelfoam pledgets are frequently used. They can be deployed rapidly, are immediately effective if the patient has a normal coagulation profile, and produce temporary vascular occlusion. Gelfoam sponge is easily cut into pieces appropriate to the caliber of the vessel to be embolized. Coils may be used with, or instead of, Gelfoam. However, if used, they may hamper future access to the hypogastric artery in the event of rebleeding. Small embolic materials such as Gelfoam powder or Ivalon particles are not used to treat hemorrhage from pelvic trauma. They produce very peripheral occlusion of small vessels, thereby risking ischemia of nontarget organs. Complications specific to pelvic embolization are extremely uncommon. Nontarget embolization is rare.

Tumors

Renal Cell Carcinoma

Primary renal cell carcinoma (RCC) is treated by surgical excision. In some cases, preoperative occlusive embolization of the renal artery is used as an adjunct to surgery. Embolization reduces intraoperative hemorrhage and allows immediate ligation of the renal vein. It is used in patients with very large tumors and also in tumors supplied by many parasitized vessels. Embolization accentuates cleavage planes and therefore facilitates nephrectomy. The optimal time delay between embolization and surgery is probably 1 day. Embolization may also favorably impact patient survival (Zielinski et al, 2000). A new application is to use selective embolization of a renal tumor as an adjunctive measure prior to radiofrequency or cryoablation of the tumor (Yamakado et al, 2006).

Palliation of nonresectable disease that causes pain and hematuria can be achieved by transcatheter embolization (Munro et al, 2003). Patients with bilateral RCC, and those with RCC in a single kidney, can undergo subselective embolization as an alternative to surgery, thereby sparing normal parenchyma. Embolization of RCC metastases to bone is performed before surgical resection to decrease intraoperative blood loss (Chatziioannou et al, 2000). CT or magnetic resonance imaging (MRI) may be used for tumor evaluation before and after intervention.

A transfemoral aortogram and selective arteriogram are performed to determine the blood supply to the kidney and tumor. An occlusive balloon catheter may be placed within the vessel and inflated before embolization to prevent reflux of embolic material and inadvertent nontarget embolization. However, many physicians use a simple selective catheter. Gelfoam pledgets are used for preoperative embolization (Figures 7–3A, B). Coils are not used because they can be dislodged during surgery when the kidney is manipulated. Absolute ethanol is the preferred embolic material for ablative palliative embolization of nonresectable tumor. Bone metastases are embolized by positioning a microcatheter in the vessel(s) supplying the tumor and injecting particles of polyvinyl alcohol (PVA) or other embolic agents such as embospheres until maximal obliteration of the angiographic tumor stain is achieved.

Tumor embolization is a safe procedure. Complications such as puncture-site hematoma and inadvertent nontarget embolization occur in <2% of patients. Almost all patients, however, experience postembolization syndrome (PES). PES consists of severe pain, nausea and vomiting, fever, and leukocytosis. It is probably caused by tissue necrosis that results from successful embolization. Transient ileus, transient hypertension, sepsis, and reversible renal failure have also been described. PES occurs within a few hours of the procedure and may last for several days. Its occurrence should not delay surgical intervention. Tissue swelling and tissue gas formation are seen on imaging studies. The severity of PES is related to the quantity of infarcted tissue. Analgesics and antibiotics are used for treatment. Administration of steroids and antibiotics before embolization may reduce the severity of PES.

Angiomyolipoma

Selective embolization has proved to be an effective method of controlling hemorrhage from benign renal lesions while preserving normal parenchyma (Kothary et al, 2005). This technique has been used in the treatment of active bleeding from angiomyolipoma and for the elective prevention of hemorrhage, especially if the tumors are multiple or bilateral, as in patients with tuberous sclerosis. Current guidelines suggest electively embolizing any tumors that are larger than 4 cm in diameter. The procedure is effective in decreasing tumor size and in preventing or treating hemorrhage in 85–90% of patients. CT can clearly identify the fat component of the tumor and is therefore used for diagnosis before intervention and for follow-up (Halpenny et al, 2009).

The technique for embolization is similar to that described for RCC. Through a transfemoral approach, angiography is used to define the arterial supply to the kidney and tumor. The feeding vessels are then selectively catheterized using a coaxial microcatheter. The tumor volume is estimated, and an equal amount of absolute ethanol admixed with iodized oil is carefully injected until the flow ceases. Ethanol is easy to handle, is inexpensive, and produces permanent occlusion of the vascular bed. Iodized oil is radiopaque and therefore is useful for visualizing the flow of the embolic material during the embolization. It remains within the tumor, thereby allowing measurement of tumor response on follow-up CT. An occlusion balloon is reserved for more proximal embolization in a main renal artery when the risk of nontarget embolization is greatest.

The reported complications are similar to those seen after RCC embolization. Recurrence of tumor hemorrhage occurs in approximately 10–15% of patients and is treated by repeat embolization. A short-term tapered dose of prednisone may reduce PES after the procedure (Bissler et al, 2002).

Ablation of Renal Function

Total renal infarction using transcatheter embolization may be indicated in certain circumstances: namely, abolition of urine production to assist in healing or palliation of terminal patients with urinary fistulas; prevention of excessive proteinuria; management of uncontrollable hypertension; rarely for benign obstructive uropathy in patients who are poor surgical candidates (De Baere et al, 2000; Toussi et al, 2001); and for ablation of failed renal allografts causing the graft intolerance syndrome (Delgado et al, 2005). For patients with end-stage renal disease and intractable hypertension or nephrotic syndrome, the advantages of ablation must be weighed against the loss of production of vitamin D3 and erythropoietic factors and, occasionally, the loss of the ability to eliminate some water. Total renal ablation must be achieved so that perfusion of surviving parenchyma via pericapsular branches cannot occur. The embolic agent must perfuse the entire renal substance but be safe if it passes through the kidney into the venous circulation. The technique is applicable in adults and children and in both native and allograft kidneys. Renal ablation appears to be a safe procedure, which is successful in most patients (De Baere et al, 2000).

Initially, a midstream aortogram is performed to identify the arterial supply to the kidneys. This is followed by renal artery catheterization and selective arteriography. An occlusion balloon catheter is placed in the vessel and contrast medium is injected to measure the volume of embolic agent needed to fill the vascular tree of the kidney. Absolute ethanol is the embolic agent of choice for the reasons mentioned above. An equal volume is carefully injected with the balloon inflated to prevent reflux to nontarget regions. The contents are then aspirated and an angiogram is performed to assess flow. The procedure is repeated as many times as necessary until complete cessation of blood flow is achieved.

PES of several days' duration occurs in all patients and is managed with antibiotics and analgesics. Inadvertent embolization of the adrenal artery and other visceral vessels is a rare but serious complication that can be avoided by using the occlusion balloon technique. Systemic toxicity from ethanol injection is not a clinical problem. Morbidity and mortality from the procedure is less than that from surgical nephrectomy.

Embolization of Primary Varicocele

The subject of varicocele and male infertility is discussed in another chapter. A recent Cochrane analysis concludes that: “There is no evidence that treatment of varicoceles in men from couples with otherwise unexplained subfertility improves the couple's chance of conception” (Evers et al, 2009). The basis for intervention is the presence of a varicocele on physical examination; most varicoceles are left sided. Color Doppler sonography is usually performed routinely before intervention. Several reports have suggested a positive association between improvement of seminal parameters and pregnancy. Surgery and percutaneous transvenous embolization appear to be equally effective (Bechara et al, 2009). However, advantages of the percutaneous route include greater patient comfort, ease of bilateral treatment, and reduced recovery time.

The procedure is performed with conscious intravenous sedation and local anesthesia. The transjugular venous approach is preferred by many physicians, although the procedure can be performed transfemorally. Direct ultrasound guidance is used to access the jugular vein; a catheter is then guided fluoroscopically into the left gonadal vein. The left gonadal vein usually drains into the left renal vein, whereas the right gonadal vein usually drains directly into the inferior vena cava. The patient is placed in reverse Trendelenburg position and left gonadal venography is performed. A positive venogram result demonstrates incompetence with filling of collateral vessels. Embolization is achieved by placing coils within the gonadal vein, commencing at the region of the inguinal ligament, and continuing cranially toward the renal vein, until the gonadal vein and collateral vessels have been occluded. If a right-sided varicocele is also present, the right gonadal vein is then interrogated and embolized.

The recurrence rate of varicocele after embolization is approximately 4%. Minor complications include contrast extravasation from perforation of the vein, nontarget embolization, venospasm, and hematoma. Rarely, cardiac arrhythmia and contrast allergy can occur.

Embolization of Ovarian Vein Varices (Pelvic Congestion Syndrome)

Pelvic congestion syndrome is a recognized cause of chronic pelvic pain in women that has been associated with lumbo-ovarian vein varices. Dyspareunia, when present, may be a poor prognostic indicator. Symptoms are often worse with fatigue, before menstruation, and in the upright position. Occasionally, vulval and thigh varicosities are present on examination. The cause is probably multifactorial. The diagnosis of varicosed pelvic veins is confirmed by duplex Doppler ultrasound that is also used for postintervention follow-up. CT venography or magnetic resonance venography are alternative noninvasive diagnostic tests.

Transvenous embolization has produced durable relief of symptoms in most patients (>70%). Most responses occur within 2 weeks of treatment; however, continued improvement has been reported up to 12 months after the procedure (Kim et al, 2006). Using either a transfemoral or a transjugular approach, the ovarian veins are individually catheterized, and embolic agents such as coils or synthetic glue are deployed in the vessel at the level of the pelvic inlet (Figures 7–4A, B). Occasionally, embolization of internal iliac vein tributaries may be necessary. Reported complications are similar to those for varicocele embolization. The procedure does not appear to have a deleterious effect on fertility or the menstrual cycle.

Treatment of High-Flow Priapism

High-flow priapism is a fairly rare condition resulting from increased arterial flow into the lacunar spaces of the cavernous tissue. The “arteriocavernous fistula” most often results from penile or perineal trauma. In some cases, the cause is unknown. Color Doppler sonography demonstrates the abnormality.

Transcatheter embolization is a minimally invasive, successful treatment for this condition (Kojima et al, 2009). A nonselective transfemoral pelvic angiogram is performed to demonstrate the fistula that originates from the pudendal artery. This procedure is followed by superselective catheterization of the injured artery using a microcatheter. The fistula is then closed by accurately deploying microcoils (Figures 7–5A, B). This technique preserves blood flow to the penis, thereby allowing normal erectile function in most cases. The use of microcoils prevents possible ischemic injury to the perineum. In the event of recurrence after embolization, repeat embolization is successful in nearly all patients. Surgery should be reserved for patients in whom embolization fails.

Ischemic nephropathy due to atherosclerotic vascular disease and renal artery stenosis is a leading cause of progressive renal failure. Renal artery stenosis is the most common cause of secondary hypertension. Surgical revascularization is an established method of treatment, with reported success rates of >70%. In recent years, percutaneous transluminal angioplasty (PTA) and stent placement have become an established alternative to surgery. These endovascular techniques are now the most common means of revascularization. However, there is great controversy over the relative benefits of revascularization compared to best medical treatment (Uder and Humke, 2005; White, 2006). In 2009, a randomized unblinded trial of treatment of over 800 patients with atherosclerotic renovascular disease by revascularization and medical therapy was compared with medical treatment alone. The conclusion of this “ASTRAL” trial was: “We found substantial risks but no evidence of a worthwhile clinical benefit from revascularization in patients with atherosclerotic renovascular disease” (ASTRAL investigators 2009). The trial has been heavily criticized for its inclusion bias and selection of end points and it is likely that properly selected patients do benefit from revascularization (White, 2010).

Streichen et al (2010) reviewed the literature on primary stenting for atherosclerotic renal artery stenosis (ARAS). They concluded, “Recent evidence shows that impaired renal function associated with ARAS is more stable over time than previously observed. Optimal medical treatment should be the preferred option for most patients with ARAS. Only low-level evidence supports compelling indications for revascularization in ARAS, including rapidly progressive hypertension or renal failure and flash pulmonary edema.”

However, other authors continue to emphasize the value of stenting: “ARAS may result in progressive renal impairment, renovascular hypertension, and/or cardiac disturbance syndromes. Because medical therapy does not affect the progressive nature of this disease process, more aggressive treatments are needed to definitively treat ARAS. When performed correctly, renal artery stenting has been shown to stabilize or improve renal function and/or renovascular hypertension in 65–70% of carefully selected patients with ARAS. Therefore, percutaneous renal artery stenting should be considered the primary treatment for patients with symptomatic ARAS (Carr et al, 2010).

PTA is the treatment of choice in the management of fibromuscular dysplasia occurring in a subset of hypertensive patients. The technique involves the use of an inflatable balloon catheter that is positioned endoluminally across the stenosis and then inflated (angioplasty).

Several diagnostic imaging modalities are used for patient selection and for postprocedure follow-up, including captopril radioisotope assay, duplex Doppler ultrasound, CT angiography, magnetic resonance angiography, and arteriography. The advantages and disadvantages of these techniques are beyond the scope of this chapter, but noncatheter angiography by CT or MR is replacing catheter angiography for diagnostic purposes.

Renal artery stenosis is described as ostial, nonostial, or branch vessel stenosis. An ostial lesion is located within 3 mm of the aortic lumen and is typical of atherosclerotic vascular disease. In fibromuscular dysplasia, nonostial and branch vessel lesions are more typically seen. The initial technical success rate of PTA varies. It may be as low as 35% for some atherosclerotic vascular disease ostial lesions, but in most series the overall rate approximates 95–100%. PTA results in stabilization or improvement of renal function in most patients with ischemic nephropathy and also leads to durable improvement or cure in most of those with hypertension. The best results after PTA have been achieved in hypertensive patients with fibromuscular dysplasia, in whom improvement or cure is achieved in approximately 90%.

Stent placement is usually the method of choice for endoluminal recanalization. Previously, stenting had been reserved for immediate failure or complication of PTA, such as elastic recoil or flow limiting intimal dissection, for residual stenoses of >30%, for a >20 mm Hg peak systolic pressure gradient after PTA, for early restenosis, and for ostial lesions that are difficult to treat by PTA alone. Renal artery stenting results in stabilization (38% of patients) or improvement (30% of patients) of renal function and in durable improvement (49%) or cure (20%) of hypertension (Leertouwer et al, 2000). PTA and stenting have also been used successfully to treat renal allograft artery stenosis. Primary patency rates vary after stenting. The average restenosis rate is approximately 17% after 6–12 months' follow-up. However, the rate increased to 20–30% with longer follow-up. Secondary patency may be achieved in >90% of patients.

Usually, the transfemoral approach is used, although a transaxillary approach may be required. Initially, a midstream aortogram is performed to identify the renal arteries, followed by a selective injection to evaluate the morphology and location of the stenosis, the diameter of the vessel, and the percentage of stenosis. In the presence of altered renal function with elevated creatinine levels, alternatives to iodinated contrast agents include gadolinium and carbon dioxide gas. Indicators of a significant stenosis include a reduction of cross-sectional diameter of at least 50%, poststenotic dilatation, collateral vessels to the affected kidney, and a transstenotic systolic pressure gradient of >20 mm Hg across the lesion. Before intervention, an oral antiplatelet agent such as clopidogrel is administered. The patient is heparinized and a vasodilating agent (eg, nitroglycerine) is given via the arterial catheter. Initially, the lesion is crossed with a guidewire. If a high-grade stenosis is present, predilatation with a small balloon may be necessary before definitive angioplasty or stent placement. An outer guiding catheter or sheath is used to facilitate contrast injection during the procedure and to improve catheter stability. Continuous fluoroscopic guidance and “vascular road-mapping” are also used to ensure precision. Frequently, a small tear in the vessel intima is seen after PTA. We prefer to use a balloon expandable stent because it can be very accurately deployed. The minimal recommended vessel diameter for stenting is 5 mm. A 10- to 20-mm-long stent is used, and approximately 1–2 mm should protrude into the aortic lumen when ostial lesions are treated (Figures 7–6A, B).

Success of the procedure is defined by <30% residual stenosis and by the resolution of a significant transstenotic pressure gradient. We frequently use a percutaneous closure device to achieve hemostasis. Antiplatelet medication is continued for 6 weeks after the procedure, and the patient is carefully followed up by clinical evaluation and repeat imaging.

The reported complication rate after PTA and stenting varies considerably but ranges from 3% to 10% in experienced operators. Complications include puncture-site hematoma; femoral artery pseudoaneurysm; contrast nephropathy; cholesterol embolization; stent malpositioning; and injury to the renal artery such as dissection, thrombosis, and rupture. Rarely, procedure-related deaths have occurred. The use of endovascular distal protection devices when stenting the carotid arteries may provide benefits for renal artery stenting. These devices are usually small filters that trap micro emboli that may be dislodged during stent placement. They limit end-organ embolization (Dubel and Murphy, 2008).

Catheter-Based Renal Sympathetic Denervation for Treatment of Resistant Hypertension

A recently developed catheter can be used by a standard transarterial endovascular route to deliver radiofrequency energy in the lumen of the renal artery. This causes selective renal denervation and reduction of sympathetic activity, resulting in a sustained reduction in hypertension. Patients with normal renal arteries and essential hypertension resistant to antihypertensive drug therapy have been successfully treated using this new technique with excellent results and minimal complications. There are very encouraging initial reports of a randomized prospective trial covering a 6-month period and a more recent publication with good results at 2 years follow-up (Esler et al, 2010; Sapoval et al, 2012; Symplicity HTN-1 Investigators, 2011).

Renal Artery Aneurysms

Renal artery aneurysms are rare and are usually not symptomatic. They carry the risk of rupture, with associated life-threatening hemorrhage. Occasionally, they are associated with renovascular hypertension. Distal embolization may occur, leading to parenchymal infarction. The indications for treatment of renal artery aneurysms include diameter >2.5 cm, interval enlargement, renovascular hypertension, pain, hematuria, intrarenal thromboemboli, and lesions in women of childbearing age. The diagnosis is made by color Doppler sonography, CT, or MRI.

In the high-risk surgical patient, endovascular techniques may be well suited to aneurysm repair, by excluding the aneurysm while preserving flow to the kidney. Depending on the location of the aneurysm, its relationship to branch vessels, and the presence or absence of a “neck,” either a stent graft or transcatheter embolization are possible treatment options (Horowitz et al, 2005; Eskandari and Resnick, 2005; Saltzberg et al, 2005). A stent graft is a metallic stent that is covered by surgical graft material. Its deployment across the aneurysm results in internal reconstruction of the vessel, with exclusion of blood flow to the aneurysm due to the impervious graft material. The cavity of the aneurysm may then thrombose.

Selective embolization of an aneurysm that is supplied by a branch vessel is performed by occluding blood flow proximally using coils. This approach results in distal parenchymal infarction and therefore can only be safely performed if there is sufficient renal functional reserve. If there is an identifiable neck separating the aneurysm from the native vessel, coils may be used to pack the aneurysm cavity, thereby resulting in thrombosis of the aneurysm while at the same time preserving distal flow. The risks of the procedure are similar to those reported above. Long-term results of endovascular repair are not yet available.

This procedure has been used extensively in the peripheral vasculature but only with limited success in the management of native renal artery or aortorenal bypass graft thrombosis. Small series or individual case reports have suggested a possible role in the treatment of recent renal artery occlusion before PTA and for the treatment of acute renal artery thromboembolic disease (Nakayama et al, 2006).

There is a variety of mechanical devices to remove clot in addition to or as an alternative to pharmacologic thrombolysis (Siablis et al, 2005). The diagnosis is made by noninvasive imaging such as duplex Doppler ultrasound, MRI, or CT angiography and is then confirmed by angiography, at which time fibrinolytic therapy is begun. A diagnostic arteriogram is performed from a transfemoral approach, after which an infusion catheter or wire is embedded within the thrombosed segment. Tissue plasminogen activator (t-PA) is currently the most frequently used fibrinolytic agent in the United States. Several infusion protocols exist. Our preferred technique is continuous infusion of 1–2 mg t-PA/hour. Prophylactic antibiotics are administered. The patient is monitored for puncture site and systemic bleeding in the intensive care or step-down unit throughout the infusion therapy. A repeat arteriogram is performed 12–24 hours after the initiation of therapy. When recanalization has been achieved, an underlying stenotic lesion is usually identified, at which time PTA or stenting is performed.

Complications include puncture site and systemic hemorrhage and infection. Bleeding may be severe enough to require transfusion or to discontinue the infusion. The incidence of complications is related to the duration of therapy and the dose administered.