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Renal Arteriovenous Malformation

Author: Mark R Wakefield, MD, Assistant Professor of Surgery/Urology, Division of Urology, University of Missouri School of Medicine; Director, Renal Transplantation, University Missouri Health Care
Coauthor(s): Julie M Riley, MD, Resident Physician, Department of Urology, University of Missouri Columbia
Contributor Information and Disclosures

Updated: Mar 10, 2009

Introduction

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 renal artery aneurysms.

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.

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.

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 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. Its 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.

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.

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.

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 eMedicine topic, Nephrogenic Fibrosing Dermopathy. 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 imagining. The use in diagnosing renal arteriovenous fistula after renal biopsy was described in a recent case report by Cheng.²

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.

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