Renal Arteriovenous Malformation

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Background

Renal arteriovenous malformations (AVMs) are abnormal communications between the intrarenal arterial and venous systems. These malformations are either congenital or acquired (often by iatrogenic means). Renal arteriovenous malformations (AVMs) are usually identified during the evaluation of gross hematuria. Treatment can be tailored to the individual patient. Options for therapy range from observation to embolization to nephrectomy.

Renal arteriovenous malformation (AVM) usually refers to the congenital type of malformation. Two types of congenital renal arteriovenous malformations (AVMs) are described. The cirsoid arteriovenous malformation (AVM) is the most common type, and the cavernous congenital arteriovenous malformation (AVM) is less common. On the other hand, acquired renal arteriovenous anomalies are often termed renal arteriovenous fistulas. Idiopathic renal arteriovenous fistulas have the radiographic characteristics of acquired fistulas, but no cause can be identified. They may be associated with intrarenal artery aneurysms that erode into a vein.


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Arteriogram demonstrating large right renal arteriovenous malformation with early filling of the vena cava.

History of the Procedure

Renal arteriovenous malformations (AVMs) were described first in 1928 by Varela. Angiographic embolization is the preferred treatment for symptomatic arteriovenous malformations (AVMs) and has been used since the mid 1970s. Nephrectomy and partial nephrectomy are more invasive treatment options. The first planned nephrectomy was accomplished in 1869 by Simon for the treatment of ureterovaginal fistula. The first partial nephrectomy was performed for a nonmalignant renal mass by Wells in 1884.

Problem

Renal arteriovenous malformations (AVMs) and fistulas include various abnormal connections between the intrarenal arterial and venous systems. They cause hematuria and are associated with hypertension.

Epidemiology

Frequency

Renal arteriovenous malformations (AVMs) are uncommon. The estimated rate in large autopsy series is less than 1 case per 30,000 patients. In clinical studies, which usually include patients undergoing evaluation with urologic or vascular imaging techniques, the incidence ranges from 1 case per 1000-2500 patients. They account for less than 1% of all types of arteriovenous malformations among the general population.

Congenital arteriovenous malformations (AVMs) account for less than one third of renal arteriovenous malformations (AVMs). Most of these are the classic cirsoid type. Congenital cirsoid arteriovenous malformations (AVMs) have a dilated, corkscrew appearance, much like a varicose vein. Cavernous arteriovenous malformations (AVMs), with single dilated vessels, account for the remainder of congenital malformations.

Acquired arteriovenous fistulas are the most common and represent as many as 75-80% of renal arteriovenous malformations (AVMs).

Idiopathic renal arteriovenous fistula represents less than 3% of renal arteriovenous malformations (AVMs).

The international incidence of renal arteriovenous malformations (AVMs) is influenced by the prevalence of percutaneous renal surgery and biopsies because these interventions cause most of the acquired renal fistulas.

Etiology

The etiology of congenital arteriovenous malformations (AVMs) is unknown. Conversely, the cause of acquired arteriovenous malformations (AVMs) is usually known.

Percutaneous renal biopsy is the most common known cause of acquired renal arteriovenous fistula. An estimated 15-50% of biopsies result in some degree of fistula formation. In one study in which arteriograms were performed after every renal biopsy, radiographic evidence of fistula was identified in 15% of patients.

Trauma is another important, although uncommon, cause of acquired renal fistulas. In patients with hypertension following renal trauma, renal arteriovenous malformations (AVMs) may occur in one third of patients. In patients with penetrating trauma, arteriovenous fistulas may affect as many as 80% of patients with posttraumatic hypertension. Trauma during ureteroscopy, percutaneous nephrostolithotomy, or after partial nephrectomy has recently been described as a cause of intrarenal arteriovenous fistula.[1]

Idiopathic arteriovenous fistulas are thought to arise from the spontaneous erosion or rupture of a renal artery into a nearby renal vein.

Arteriovenous malformations (AVMs) may also occur in the setting of malignancy. Renal cell carcinoma has a vascular predilection, with renal vein extension and parasitic tumor vessels both being relatively common. Angiogenic tumor factors have been implicated and may explain the development of arteriovenous malformations (AVMs) within renal tumors.

Pathophysiology

In the cirsoid congenital arteriovenous malformation (AVM), multiple communications exist between the arteries and veins. These communications develop multiple coiled channels, forming a mass within the renal parenchyma. The communicating vessels are tortuous, dilated, and located beneath the lamina propria of the renal urothelium. This cluster of vascular channels forms a mass, with the arterial supply arising from one or more segmental or interlobar renal arteries. Microscopic features of these arteries and veins involved are identical to their normal soft tissue counterparts. Occasionally, there may be some associated thromboses. Their nearness to the collecting system may explain the high prevalence of hematuria.

The less common cavernous congenital arteriovenous malformation (AVM) is characterized by a single artery that feeds into a single cystic chamber, with a single draining vein.

Acquired arteriovenous malformations (AVMs) result from traumatic disruption of renal vessels. A fistulous connection between the arterial and venous systems occurs as a result of the trauma.

Any renal arteriovenous malformation (AVM) may result in renin-mediated hypertension.

Presentation

Gross hematuria is the initial sign or symptom in most (as many as 75%) patients with a renal arteriovenous malformation (AVM).

Renal colic may result from obstructing blood clots, which may be voided as vermiform (wormlike) masses.

Rarely, during the evaluation of asymptomatic microscopic hematuria, an arteriovenous malformation (AVM) is found and presumed to be the cause of hematuria.

A significant percentage of patients with renal arteriovenous malformations (AVMs) are hypertensive. Half the patients with acquired arteriovenous malformations (AVMs) and a quarter of the patients with congenital renal arteriovenous malformations (AVMs) have high blood pressure. Pre-existing hypertension is thought to be a risk factor for developing a fistula following a renal biopsy. Conversely, hypertension that develops following a biopsy can be due to increased renin secretion that is caused by relative hypoperfusion distal to the arteriovenous malformation (AVM).

Cardiomegaly, congestive heart failure (CHF), or both also may be present among patients evaluated for renal arteriovenous malformations (AVMs).

Rarely, a patient may present with hypotension from hemorrhage caused by an arteriovenous malformation (AVM). This has been described in numerous settings, including during pregnancy.

Occasionally, renal AVMs may mimic renal cell carcinoma and only be identified on surgical pathology.

AVMs have also been found to worsen kidney function in patients with chronic kidney disease.[2]

A history of a previous renal biopsy or percutaneous renal surgery is an important risk factor for the development of an acquired arteriovenous fistula. A history of renal trauma, especially a penetrating injury, is also an important risk factor for developing a renal fistula.

A physical evaluation may demonstrate findings of a flank bruit. A palpable mass is usually present in those patients with renal tumors as the cause of the fistula.

Indications

Gross hematuria is the primary reason for evaluation of patients with renal arteriovenous malformations (AVMs). The diagnostic evaluation of patients with microscopic hematuria also may lead to the discovery of an arteriovenous malformation (AVM). Flank pain may lead to the diagnosis of arteriovenous malformation (AVM), although this is unusual without the presence of hematuria. Several case reports describe the incidental discovery of arteriovenous malformations (AVMs) on images from studies performed for other indications.

The initial means of treating renal malformation is usually arteriographically guided embolization. One indication for the treatment of renal arteriovenous malformations (AVMs) is pain. The pain from renal arteriovenous malformations (AVMs) results from either obstruction of the collecting system by clots or from the expansion of the renal capsule due to intrarenal hemorrhage. Persistent gross hematuria, especially in patients with anemia, may prompt treatment.

Hypertension is an important indication for treatment. Attempts have been made to preoperatively determine whether the malformation is responsible for the hypertension. However, selective renal vein renin levels have not been successful in helping discriminate which patients' hypertension will respond to either embolization or nephrectomy. Congestive hear failure (CHF) is an unusual yet compelling indication for treatment. Several case reports have described patients in severe heart failure whose cardiac health improved to normal limits after nephrectomy or embolization of the AVM.[3]

Indications for surgical therapy have become more restricted as the ability to treat renal arteriovenous malformations (AVMs) with angiographic embolization has improved. Arteriovenous malformations (AVMs) due to malignancy usually require surgical extirpation. Significant metastatic disease and poor performance status may limit the use of nephrectomy, in which embolization may be palliative. Symptomatic hematuria refractory to embolization is definitively treated by nephrectomy. In most cases, hypertension is cured by nephrectomy. Finally, pain refractory to less-invasive attempts may respond to nephrectomy.

Relevant Anatomy

Knowledge of renal vascular anatomy is important in understanding diagnostic studies and planning therapy.

The renal artery is an end-organ branch from the aorta. Supernumerary renal arteries are common (at least 25% of patients). The renal artery branches into 4 or 5 segmental renal arteries. The first branch is the posterior branch, which supplies the posterior segment of the kidney. The main artery then enters the renal hilum before dividing into the other segmental branches.

These branches of the renal artery supply minimal collateral circulation among the renal segments. The lobar renal arteries are located within the renal sinus and are branches of the segmental arteries.

The lobar arteries divide into the interlobar arteries, which are within the renal parenchyma. The interlobar arteries are in close proximity to the collecting system. The interlobar arteries divide into the arcuate arteries, which lead to the interlobular arteries.

The interlobular arteries lead to the afferent arterioles, which feed each glomerulus. Blood flows from the glomerulus to the efferent arteries, which lead to the vas recta, which, in turn, provides the network for venous drainage of the kidney.

The venous drainage follows the same pattern of branching as the arteries. However, unlike the arterial system, significant connections exist between the renal segments within the venous system.

Cirsoid AVMs are usually larger than 1 cm in diameter and are located adjacent to the collecting system. Cavernosal AVMs are less than 1 cm in diameter and are usually located near the periphery. Aneurysmal AVMs are larger than 1 cm in diameter and are located near the renal hilum.[4]

Contraindications

In general, no contraindications exist for evaluating arteriovenous malformations (AVMs).

In a patient with allergy to contrast agents, the diagnostic evaluation may need to be altered. If iodinated contrast is used for diagnostic studies in patients with previous reactions, then medical preparation may decrease the risk of severe allergic reactions.

Severe protocols have been advocated; one regimen includes (1) administering 20-50 mg of prednisone orally 13 hours, 7 hours, and 1 hour prior to the procedure and (2) administering 50 mg of diphenhydramine orally 1 hour prior to the procedure. Additionally, histamine2-receptor antagonists are used in some centers to further decrease the risk of an allergic reaction. Also, the use of nonionic contrast is associated with a lower incidence of allergic reactions.

Alternatively, diagnostic methods that do not use iodinated contrast may be used to avoid the risk of a reaction occurring. Specifically, magnetic resonance angiography (MRA) with gadolinium and carbon dioxide angiography can provide excellent images of the renal arteries and, potentially, renal arteriovenous malformations (AVMs).

Impaired renal function increases the risk of using iodinated contrast in diagnostic studies, which may alter the evaluation. Diabetes, preexisting renal insufficiency, and dehydration are risk factors for contrast-induced nephropathy. The degree of renal insufficiency that precludes the use of contrast is controversial. An absolute cut-off should be avoided. The risk of nephropathy increases if the serum creatinine level is greater than 1.5 mg/dL. In some cases, the use of contrast can be justified even in patients with moderate-to-severe renal dysfunction. Nonetheless, a serum creatinine level greater than 1.5-2 mg/dL should prompt consideration of alternative diagnostic measures (eg, digital subtraction angiography, MRA, carbon dioxide angiography).

Further, hydration with intravenous isotonic sodium chloride solution, diuresis (eg, via administration of furosemide), and the administration of free-radical scavengers may decrease the frequency, duration, and severity of contrast-induced renal dysfunction. Specific free-radical scavengers include mannitol (which also facilitates diuresis) and acetylcysteine (Mucomyst). Lower doses of contrast and nonionic media are also used to diminish the risk of contrast. In most patients, renal function recovers and dialysis is rarely needed.

Gadolinium-based contrast agents (Magnevist, MultiHance, Omniscan, OptiMARK, ProHance) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the Medscape Reference topic Nephrogenic Systemic Fibrosis. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA.

NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Often considered of historic interest, carbon dioxide contrast angiography has been increasingly used as an alternative to iodinated and gadolinium-based contrast imaging. This use in diagnosing renal arteriovenous fistula after renal biopsy was described in a recent case report by Cheng.[5] A single report in the literature suggests that owing to the buoyancy and low viscosity of carbon dioxide, in high-flow AVMs it provides more detailed information of the arteriovenous connections than iodine-based contrast. This is necessary to plan embolization. It also detects residual postembolization communications that other contrast agents do not.[6]

Few contraindications exist to treating renal arteriovenous malformations (AVMs). Contrast allergy may necessitate premedication with antihistamines and steroids. Otherwise, embolization of renal arteriovenous malformations (AVMs) is well tolerated, even among patients not able to tolerate operative intervention. However, in those patients with poor general health, especially with regard to cardiopulmonary status, surgical intervention may be contraindicated.

Additionally, renal function must be carefully assessed before nephrectomy is performed in select patients. The importance of nephron-sparing surgery is magnified in patients with underlying renal impairment. Approximately 20-25% of a single renal unit should be salvaged if possible. This provides an estimated glomerular filtration rate of 10-15%, which may keep many patients from needing dialysis for end-stage renal disease. However, ultrafiltration injury may occur when less than 25% of the total renal mass is spared.

Thus, in patients with solitary kidneys, bilateral arteriovenous malformations (AVMs), or renal insufficiency, detailed planning is necessary. The increased risk of partial nephrectomy is easily justified for these patients. Additionally, strong arguments can be made for the routine use of nephron-sparing approaches, especially for benign diseases such as renal arteriovenous malformations (AVMs), in all patients when technically feasible. This serves to protect patients from the small risk of developing renal insufficiency in the future.

Laboratory Studies

Imaging Studies

Other Tests

Diagnostic Procedures

Histologic Findings

A recent study found that the microscopic features of AVMs were histologically identical to their soft tissue counterparts. The study found AVMs to be abnormally arranged, thick- and thin-walled vessels resembling malformed veins, venules, arteries, and arterioles, occasionally with associated thromboses.[4]

Medical Therapy

In some cases, conservative therapy can be used safely. If ablation was not performed at the time of arteriography, observation is indicated in some patients. If symptoms and hemodynamic complications do not develop, noninvasive therapy is worth a trial in those patients with small arteriovenous malformations (AVMs). Hematuria often improves with bedrest. Analgesics may be necessary.

Little is known about the natural history of untreated arteriovenous malformations (AVMs). Acquired arteriovenous fistulas tend to resolve spontaneously. A recent report describes spontaneous resolution of an arteriovenous malformation (AVM). Angiography findings helped confirm the radiographic disappearance of the malformation without specific intervention. Nonetheless, theoretical concerns are that expectant therapy risks delayed hemorrhage from an enlarging arteriovenous malformation (AVM) or the development of irreversible hypertension. Because patients with arteriovenous malformations (AVMs) usually present with symptoms, most patients receive an attempt at definitive therapy rather than mere observation.

Medical management is essential to optimizing outcome. In addition to relieving pain, hypertension should be treated. Heart failure must be controlled before surgical intervention is instituted. Blood transfusions may be needed for the rare patient with hemorrhage from an arteriovenous malformation (AVM). Finally, renal failure can occur as a complication of the contrast agents used during radiographic evaluation.

The initial therapy for treatment of arteriovenous malformations (AVMs) is usually angiographically guided embolization of the malformation. Numerous substances have been injected in an effort to ablate the arteriovenous malformation (AVM). Initial attempts at embolization were complicated by recurrence of the arteriovenous malformation (AVM). This was thought to be due to the type of material used for embolization. Materials that have been used for embolization include steel coils, autologous blood clots, gelatin sponges and foams, and synthetic polymers.

The most effective material for embolization appears to be absolute alcohol, which is relatively inexpensive. Injection through the catheter lumen is also easier than with many of the synthetic materials. Balloon catheters are used to occlude the feeding artery to prevent retrograde migration of the alcohol. The alcohol denatures the proteins within the wall of the arteriovenous malformation (AVM), thereby inducing thrombosis and occlusion of the malformations. Additionally, using absolute alcohol for embolization has an antihypertensive effect because it destroys the juxtaglomerular apparatus, eliminating the excessive renin production causing increased blood pressure.[8] Superselective embolization with coils and microspheres has also been described. Care must be taken with coils to avoid migration beyond the AVM leading to the potential for pulmonary embolism. Superselective embolization has not been shown to cause any adverse effect on renal function.

Repeat treatments may be needed to completely ablate the arteriovenous malformation (AVM). Alcohol or other material can be used for the subsequent treatments. Epinephrine injection before embolization may make the procedure more effective by inducing vasospasm, thereby concentrating the injected material within the arteriovenous malformation (AVM).

Postembolization syndrome (PES), a combination of fever, leukocytosis, abdominal pain, nausea, and vomiting, is commonly described and may last 1-3 days. It should be treated with analgesia, rest, and potentially intravenous antibiotics. One study that evaluated 15 patients who underwent embolization for a renal AVM or renal artery aneurysm noted PES in 10 of 15 patients.[9]

Surgical Therapy

The treatment most likely to cure an arteriovenous malformation (AVM) is total nephrectomy. Total nephrectomy is indicated for large cirsoid arteriovenous malformations (AVMs). In most cases, nephrectomy is reserved for patients in whom more conservative therapy has failed. If the fistula is due to malignancy, then radical nephrectomy is usually indicated.

The primary criticism of nephrectomy for renal arteriovenous malformations (AVMs) is that significant amounts of normal renal tissue are removed. Thus, reconstructive approaches have been advocated in selected circumstances. Partial nephrectomy has been accepted as a safe treatment for small, polar lesions. With increasing experience with partial nephrectomy for malignancy, partial nephrectomy will likely be attempted with greater confidence, even for large and centrally located arteriovenous malformations (AVMs). Additionally, to decrease the morbidity from the incisions needed for renal surgery, laparoscopic partial and total nephrectomy have been used with increasing frequency to treat selected renal arteriovenous malformations (AVMs).

In addition to partial nephrectomy, other techniques have been used to treat arteriovenous malformations (AVMs). Small malformations located in the peripheral aspect of the kidney may be treated by ligation of feeding vessels. The dissection of the feeding vessels may be technically difficult. Bench surgery with autotransplantation may facilitate the successful treatment of large and/or centrally located malformations. This degree of renal reconstruction is rarely necessary but may preserve enough functional renal tissue to avoid dialysis in select cases.

Despite being the most successful treatment for renal arteriovenous malformations (AVMs), surgical intervention is usually reserved for those cases refractory to embolization or those associated with malignancy.

Preoperative Details

The successful treatment of renal arteriovenous malformations (AVMs) relies on definitive localization of the lesion. Meticulous radiographic evaluation is needed because some lesions are subtle.

Medical conditions, especially congestive heart failure (CHF) and hypertension, should be stabilized. Assessment of anesthetic risk is needed before open surgical intervention is pursued. Coagulopathies must be corrected before intervention. Transfusion may be needed to correct anemia.

Special attention to renal function is needed when planning operative intervention. Several circumstances exist that may impair renal function. Chronic hypertension may result in nephrosclerosis and chronic renal insufficiency. Heart failure may cause both acute and chronic renal dysfunction due to inadequate perfusion. Pharmacological therapy for either hypertension or heart failure can induce renal insufficiency. Contrast used for arteriography may cause acute renal failure, which may necessitate a delay in intervention.

Preexisting congenital anomalies, acquired abnormalities, or previous surgery may impair the function of the contralateral kidney. In these cases, global renal function should be assessed by deliberate means. The presence of hematuria can complicate 24-hour urine collection for the assessment for creatinine and urea clearance, but it can provide an accurate assessment of renal function. Nuclear scans can help assess estimated glomerular filtration rates and split renal function. These objective data can help accurately guide the need for nephron-sparing surgery, such as partial nephrectomy.

Intraoperative Details

Total or simple nephrectomy to treat renal arteriovenous malformations (AVMs) is a routine procedure in most cases. The choice of incision and surgical approach is determined by surgeon preference, as well as by patient body habitus, arteriovenous malformation (AVM) size, and previous incisions.

The flank extraperitoneal approach serves well for most cases, although a transabdominal approach offers early control of the main renal vessels, which may prove beneficial in some cases. The posterior approach may have less patient morbidity but is not a routine approach. Laparoscopic nephrectomy offers the patient less discomfort and an earlier return to normal activity.

The Gerota fascia may be entered or perinephric fat can be excised, usually depending on which approach is easiest at the time of surgery. Perinephric fibrosis due to subcapsular bleeding may make simple nephrectomy more difficult than excision of the perinephric fat with the kidney. The adrenal gland should be spared.

When partial nephrectomy or extracorporeal reconstruction is indicated, the kidney should usually be cooled with ice slush or limit ischemic time to less than 30 minutes. Mannitol may be useful to facilitate diuresis and as a free-radical scavenger. Intraoperative ultrasound provides the means to localize small lesions.

Postoperative Details

Routine postoperative care is indicated following nephrectomy, as is careful hydration and close hemodynamic monitoring. Aggressive pulmonary toilet is essential. Early ambulation is important, and activity restrictions following partial nephrectomy are becoming less stringent. Resumption of diet is influenced mostly by surgeon bias, although caution is warranted following transabdominal approaches. The influence of CHF can complicate the response to nephrectomy. In patients with arteriovenous malformation (AVM)–induced heart failure, intensive monitoring, including pulmonary artery catheterization, may be needed.

Follow-up

Individualized follow-up care is necessary following intervention. Unless total nephrectomy is used, recurrence is possible. Additionally, hypertension and renal function should be assessed. Routine imaging is not usually indicated.

For excellent patient education resources, see eMedicineHealth's patient education article Blood in the Urine.

Complications

Nephrectomy complications can be classified by organ system. Cardiac complications include dysrhythmia from electrolyte imbalances caused by diuresis. Ischemia may be caused by surgical anemia or anesthetic hypotension. Pulmonary complications include atelectasis, pneumonia, pneumothorax, and pulmonary embolism. Gastrointestinal complications include ileus, pancreatitis, and duodenal injury (from retractor tension). Subcostal nerve injury and stroke are possible nervous system complications. Infections are uncommon, although Foley catheter-induced cystitis, incisional sepsis, and pneumonia are possible.

Partial nephrectomy has more potential complications. Bleeding is more common after partial nephrectomy than after total nephrectomy. Renal impairment is also reportedly more common after partial nephrectomy. This occurs most often in the setting of preexisting renal insufficiency, which may have mandated partial nephrectomy. Acute tubular necrosis can occur; renal cooling during partial nephrectomy may decrease the duration and severity of acute tubular necrosis following partial nephrectomy. However, the necessity of renal cooling during partial nephrectomy is increasingly controversial. In experienced centers, laparoscopic partial nephrectomy can be accomplished without renal surface cooling and without a significantly increased risk of acute tubular necrosis.

However, the application of laparoscopic partial nephrectomy for the treatment of renal arteriovenous malformation (AVM) has not been well described. If the contralateral kidney is normal, renal function is usually normal postoperatively, although increased blood loss, longer duration of the operation, and reperfusion effects may rarely cause total renal impairment after partial nephrectomy.

Urinary and arteriovenous fistulas have been described after partial nephrectomy. Urinary fistulas result from an injury to the collecting system during the partial nephrectomy. Urine can drain to the skin, creating a urinary-cutaneous fistula. Most urinary fistulas and leaks can be treated successfully conservatively or with urinary drainage, often using minimally invasive techniques such as percutaneous nephrostomy and drain placement. Arteriovenous fistulas may be silent, discovered incidentally during subsequent imaging studies. They also may manifest with signs or symptoms similar to the original arteriovenous malformation (AVM). Thus, recurrence after partial nephrectomy is possible.

Complications after embolization include pharmacologic and technical factors. Contrast-induced nephropathy and allergic reactions may occur and can be serious. Further, the agent used for embolization may cause complications. The agent may migrate or be misdirected and thus cause damage to normal renal tissue or other organs. A recent case description noted coil and guidewire erosion into the colon. Alcohol may cause transient headaches and mild intoxication. Recurrence or persistent fistulas are possible. Hematomas and pseudoaneurysm at the puncture site (usually femoral artery) are not uncommon, with clinical evidence of hematoma occurring in approximately 5% of patients.

Outcome and Prognosis

Endovascular therapy with embolization is considered the treatment of choice for arteriovenous fistulas (AVFs) and arteriovenous malformations (AVMs) because it allows preservation of the unaffected renal parenchyma. A study by Takebayashi et al successfully embolized 30 cases of congenital AVM. About 60% of patients responded to embolization; however, improvement of hypertension may take up to 2-3 months.[10]

Nephrectomy remains an alternative option for treating renal arteriovenous malformations (AVMs). Hematuria due to an arteriovenous malformation (AVM) resolves following nephrectomy, while hypertension is cured or improved in 60-85% of patients.

Further, with advances in available techniques, angiographic embolization treatment is the usual first line of therapy because it can be accomplished at the time of diagnosis, with little morbidity.

Most acquired renal fistulas resolve spontaneously.

Future and Controversies

Renal arteriovenous malformations (AVMs) remain an uncommon clinical problem. However, the incidence may increase as the frequency of incidental renal masses increases. Small renal masses on abdominal imaging studies performed for other symptoms are becoming more common.

Categorizing these masses as benign or malignant in an economic and safe manner has received much attention. Asymptomatic renal arteriovenous malformations (AVMs) are a rare cause of the incidental mass, but several case reports describe clinical situations in which a renal arteriovenous malformation (AVM) was classified incorrectly as a malignant tumor or as hydronephrosis. Specific CT scan protocols seem especially promising as a minimally invasive way to improve the classification of renal masses. Further, improvements in MRI, MRA, and Doppler ultrasound may decrease the need for the use iodinated contrast agents.

Author

Mark R Wakefield, MD, Associate Professor of Surgery/Urology, Chief, Division of Urology, University of Missouri-Columbia School of Medicine; Director, Renal Transplantation, University Missouri Health Care

Disclosure: Nothing to disclose.

Coauthor(s)

Carrie E Yeast, MD, Resident Physician, Department of Urology, University of Missouri-Columbia Hospital

Disclosure: Nothing to disclose.

Julie M Riley, MD, Assistant Professor, Department of Surgery, Division of Urology, University of New Mexico School of Medicine

Disclosure: Nothing to disclose.

Specialty Editors

Richard A Santucci, MD, FACS, Specialist-in-Chief, Department of Urology, Detroit Medical Center; Chief of Urology, Detroit Receiving Hospital; Director, The Center for Urologic Reconstruction; Clinical Professor of Urology, Michigan State University College of Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Travis J Phifer, MD, Chief, Division of Vascular Surgery, Professor, Department of Surgery and Radiology, Louisiana State University Health Sciences Center in Shreveport

Disclosure: Nothing to disclose.

J Stuart Wolf Jr, MD, FACS, David A Bloom Professor of Urology, Associate Chair for Clinical Operations, Director, Division of Endourology and Stone Disease, Department of Urology, University of Michigan Medical School

Disclosure: Nothing to disclose.

Chief Editor

Vincent Lopez Rowe, MD, Professor of Surgery, Program Director, Vascular Surgery Residency, Department of Surgery, Division of Vascular Surgery, Keck School of Medicine of the University of Southern California

Disclosure: Nothing to disclose.

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Arteriogram demonstrating large right renal arteriovenous malformation with early filling of the vena cava.

Arteriogram demonstrating large right renal arteriovenous malformation with early filling of the vena cava.

MRA reconstruction of the same patient.

Transaxial image demonstrating large intrarenal arteriovenous malformation with enlarged renal vein.

CT angiographic axial image showing a likely congenital renal arteriovenous malformation (AVM) in a middle-aged woman associated with aneurysmal dilation of the left renal vein. The patient presented with an episode of syncope and mild left flank pain.

Same patient as in the previous image; CT angiogram on coronal image illustrating a prominent left arteriovenous malformation (AVM) with aneurysmal renal vein.

CT coronal reconstruction after intrarenal angiogram demonstrating 2 large renal artery aneurysms arising from the right renal artery division at the hilum, with an associated lower pole arteriovenous fistula. This was determined to be unreasonable for embolization or coiling. This patient was asymptomatic and was imaged after a trauma.