Renal arteriovenous malformations (AVMs), first described in 1928 by Varela, are abnormal communications between the intrarenal arterial and venous systems. They cause hematuria and are associated with hypertension.
Renal AVMs may be either congenital or acquired (often by iatrogenic means). More commonly, the term refers to the congenital type of malformation. Two subtypes of congenital renal AVMs are described, as follows:
On the other hand, acquired renal arteriovenous anomalies are often termed renal arteriovenous fistulas (AVFs). Idiopathic renal AVFs 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.
Renal AVMs are usually identified during the evaluation of gross hematuria. Treatment can be tailored to the individual patient. Angiographic embolization is the preferred treatment for symptomatic 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.
Renal 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 AVMs are a rare cause of the incidental mass, but several case reports describe clinical situations in which a renal AVM was classified incorrectly as a malignant tumor or as hydronephrosis. Specific computed tomography (CT) protocols seem especially promising as a minimally invasive way to improve the classification of renal masses. In addition, improvements in magnetic resonance imaging (MRI), magnetic resonance angiography (MRA), and Doppler ultrasonography may decrease the need for the use iodinated contrast agents.
For patient education resources, see Blood in the Urine.
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 four or five 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. Cavernous 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.
In the cirsoid congenital 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 AVM is characterized by a single artery that feeds into a single cystic chamber, with a single draining vein.
Acquired 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 AVM may result in renin-mediated hypertension.
The etiology of congenital AVMs is unknown. Conversely, the cause of acquired AVMs is usually known.
Percutaneous renal biopsy is the most common known cause of acquired renal AVF. 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, though uncommon, cause of acquired renal fistulas. In patients with hypertension following renal trauma, renal AVMs may occur in one third of patients. In patients with penetrating trauma, AVFs may affect as many as 80% of patients with posttraumatic hypertension. Trauma during ureteroscopy or percutaneous nephrostolithotomy or after partial nephrectomy has been described as a cause of intrarenal AVF.
Idiopathic AVFs are thought to arise from the spontaneous erosion or rupture of a renal artery into a nearby renal vein.
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 AVMs within renal tumors.
Renal 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 patients to 1 per 2500. They account for fewer than 1% of all types of AVMs among the general population.
Congenital AVMs account for fewer than one third of renal AVMs. Most of these are the classic cirsoid type. Congenital cirsoid AVMs have a dilated, corkscrew appearance, much like a varicose vein. Cavernous AVMs, with single dilated vessels, account for the remainder of congenital malformations.
Acquired AVFs are the most common and represent as many as 75-80% of renal AVMs.
Idiopathic renal AVFs represent fewer than 3% of renal AVMs.
The international incidence of renal AVMs is influenced by the prevalence of percutaneous renal surgery and biopsies because these interventions cause most of the acquired renal fistulas.
Endovascular therapy with embolization is considered the treatment of choice for AVFs and 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.
Eom et al retrospectively technical and clinical success rates, radiologic and laboratory findings, and complications of renal artery embolization for 31 renal AVMs in 24 patients. The clinical success rate after initial embolization was 67%; the overall clinical success rate, 88%; and the technical success rate, 65%. There were 11 technical failures in 10 patients. In four, clinical success was attained without additional embolization; in three, a second embolization session yielded clinical success; and in three, recurrence necessitated nephrectomy. The authors noted that technical failure did not always result in clinical failure and that multiple embolizations may be effective for recurrence.
Nephrectomy remains an alternative option for treating renal AVMs. Hematuria due to an AVM resolves following nephrectomy, and 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.
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 AVM is found and presumed to be the cause of hematuria.
A significant percentage of patients with renal AVMs are hypertensive. Half the patients with acquired AVMs and a quarter of the patients with congenital renal AVMs have high blood pressure. Pre-existing hypertension is thought to be a risk factor for developing a fistula after a renal biopsy. Conversely, hypertension that develops after a biopsy can be due to increased renin secretion that is caused by relative hypoperfusion distal to the AVM.
Cardiomegaly, congestive heart failure (CHF), or both also may be present among patients evaluated for renal AVMs.
Rarely, a patient may present with hypotension from hemorrhage caused by an 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.
A history of a previous renal biopsy or percutaneous renal surgery is an important risk factor for the development of an acquired arteriovenous fistula (AVF). A history of renal trauma, especially a penetrating injury, is also an important risk factor for developing a renal AVF.
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.
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 AVM. Flank pain may lead to the diagnosis of AVM, though this is unusual without the presence of hematuria. Several case reports describe the incidental discovery of AVMs on images from studies performed for other indications.
In general, no contraindications exist for evaluating AVMs. In a patient with allergy to contrast agents, the diagnostic evaluation may have 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, H2-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 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 [DSA], MRA, carbon dioxide angiography).
Furthermore, hydration with intravenous (IV) 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. 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 have been linked to the development of nephrogenic systemic fibrosis (NSF), or nephrogenic fibrosing dermopathy (NFD). (See 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 magnetic resonance imaging (MRI) or MRA. As of late December 2006, the US Food and Drug Administration (FDA) had received reports of 90 such cases. Worldwide, more 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 (AVF) after renal biopsy was described in a case report by Cheng. A report in the literature suggested 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 does. This is necessary to plan embolization. It also detects residual postembolization communications that other contrast agents do not.
In general, the laboratory evaluation is dictated by the clinical presentation of the patient.
Anemia may contribute to the severity of heart failure in some patients with renal AVMs. Further, significant hemorrhage and hemodynamic instability are associated with AVMs. In these cases, frequent assessment of the hemoglobin and hematocrit values is indicated.
The assessment of renal function based on serum creatinine values is indicated before contrast-enhanced radiographic studies are performed, especially in elective scenarios and in high-risk patients (eg, patients with diabetes, those older than 65 years, and those with known renal insufficiency).
Renal function may also dictate the type and timing of surgical intervention. Nephron-sparing surgery with partial nephrectomy is an important treatment option in patients with preexisting renal failure. Additionally, the diagnostic evaluation may be modified in patients with renal insufficiency. Finally, obstructive uropathy may result from gross hematuria with clots. Surgical intervention (if not emergent or needed to relieve the obstruction) should be delayed until maximal recovery of renal function is achieved.
Coagulation parameters (ie, prothrombin time, activated partial thromboplastin time, and bleeding time) may be helpful. Coagulopathies may be responsible for bleeding that reveals the presence of an AVM. Bleeding disorders should be corrected before most interventions are pursued.
The availability of typed and crossmatched blood becomes important in hemodynamically unstable patients.
The renal vein renin test is a way to test for renovascular hypertension. Radiology places a catheter in the groin area at the femoral vein. The catheter is placed up to the level of each renal vein, and a blood sample is taken. Normally, both kidneys secrete the same amount of renin; a patient with hypertension due to an AVM has increased renin levels on the side of the AVM.
Rarely, renal AVMs may be discovered during the evaluation of microscopic hematuria. Urinary tract infections (UTIs) should be excluded before intervention is pursued.
The initial diagnostic evaluation of hematuria is debatable. No single study detects all pathologies. Renal ultrasonography has been advocated as an ideal initial study because renal ultrasound is noninvasive, relatively inexpensive, and helps to detect many lesions.
Until relatively recently, most urologists favored the use of intravenous pyelography (IVP) for the initial evaluation of patients with hematuria. Computed tomography (CT) has been gaining favor in some centers because of the speed of the study and the detailed images of the renal parenchyma. With modern scanners and software, collecting system evaluation is also improving. Three-dimensional reconstruction with tailored studies can provide excellent anatomic detail.
Thus, the initial study for the evaluation of gross hematuria depends on several factors, including location, urologist and radiologist preference, and patient factors. The characteristics of renal AVMs on IVP, ultrasonography, and CT are described below.
The advantages of IVP in thsi setting include obtaining anatomic detail, especially of the collecting system, and functional information about perfusion, function, and obstruction. The disadvantages include cost, radiation and contrast agent exposure, and insensitivity for small mass lesions.
In numerous cases, additional radiographic studies are needed, but, in most cases, IVP is a reasonable initial study for the evaluation of gross hematuria.
AVMs have several characteristics on IVP images. A mass lesion may be observed on the nephrotomogram images, especially in the medullary region, with compression of the collecting system. Hypoperfusion distal to the AVM may be present, which manifests as a wedge-shaped defect or segmental nonvisualization. Filling defects of the collecting system may also be present. The AVM may cause an irregular impression on the collecting system, and clots may fill and obscure a calyx or the renal pelvis. Finally, IVP results may be normal in patients with an AVM.
Ultrasonography has recently gained favor as a noninvasive means for evaluating renal causes of hematuria. The debate about the merits of ultrasonography versus IVP for this purpose is beyond the scope of this article.
Ultrasonography is more sensitive for the detection of small renal masses and can help distinguish more reliably between cystic and solid masses. However, renal ultrasonography is less accurate for identifying lesions of the collecting system and provides only indirect information about renal function.
Doppler increases the sensitivity for vascular lesions. Several cases have been reported in which a mass lesion was correctly identified as a renal AVM by the use of color-duplex Doppler ultrasound studies. The lesions were identified as AVMs on the basis of the turbulent blood flow within a cystic mass. Otherwise, ultrasonography may not be able to help distinguish AVMs from small solid masses.
Further evaluation of renal lesions detected by means of ultrasonography or IVP usually includes CT of the kidney. Standard abdominal scans with drip infusion of contrast may help identify an enhancing mass lesion of the kidney, often centrally located near the collecting system.
To differentiate such a mass from a hypervascular mass (eg, renal cell carcinoma), specific dynamic renal protocols are useful. These include noncontrast scans followed by bolus infusion of contrast. Soon after contrast administration, the patient is rescanned several times to capture the sequential stages of contrast uptake in the kidney.
Typical findings include early filling of the renal vein and inferior vena cava with contrast, dilation of the renal vein, and, sometimes, enlargement of the feeding renal artery. Dense contrast enhancement of the lesion during the cortical phase may be helpful, especially if the mass is located in the medulla, which typically has less early contrast enhancement.
With modern spiral CT scanners and bolus infusion, detailed anatomic and functional information can be obtained and can lead to the accurate diagnosis of renal AVMs.
In some centers, CT urography has replaced IVP for the initial evaluation of hematuria. With proper equipment and oversight, CT urography, CT angiography (CTA), or both can provide information about renal function, as well as detailed definition of the anatomy, including the vascular and collecting systems.
In current practice, CTA has replaced traditional angiography for many indications, including evaluation of the living kidney donor and preoperative planning for complex partial nephrectomy. (See the images below.)
CT angiographic axial image showing a likely congenital renal arteriovenous malformation (AVM) in a middle-aged woman associated with aneurysmal dilat....
Same patient as in the previous image; CT angiogram on coronal image illustrating a prominent left arteriovenous malformation (AVM) with aneurysmal re....
Angiography remains the criterion standard for the clinical diagnosis of AVM. Additionally, angiography provides the means for treatment with transcatheter embolization. (See the image below.)
Arteriogram demonstrating large right renal arteriovenous malformation with early filling of the vena cava.
Angiography of an AVM demonstrates rapid contrast visualization in the inferior vena cava within seconds of contrast injection because of the rapid shunting of blood from the arterial system to the venous system. Decreased density on the nephrogram also may appear distal to the AVM. The actual malformation may be a subtle blush if the AVM is small, or the multiple small tortuous vessels may be easily visualized. Cirsoid AVMs are supplied by multiple arteries, whereas cavernous AVMs and AVFs tend to be supplied by single vessels.
MRA is a promising technology for the evaluation of renal masses. It is especially useful in those patients who cannot tolerate iodine-based contrast. Several reports have confirmed the diagnostic usefulness of MRA for the diagnosis of renal AVM. (See the image below.)
MRA reconstruction of the same patient.
Because most patients with AVMs present with hematuria, cystoscopy should be performed to evaluate for coincidental lower tract pathology.
Urine cytology is usually performed during the evaluation of hematuria, though it does not specifically contribute to the diagnosis of a renal AVM. Cytologic evaluation of the urine is also useful for screening for carcinoma in situ of the bladder, which can be missed during diagnostic cystoscopy.
One 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.
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 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 determine which patients' hypertension will respond to either embolization or nephrectomy. Congestive heart 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.
Indications for surgical therapy have become more restricted as the ability to treat renal AVMs with angiographic embolization has improved. AVMs due to malignancy usually must be surgically extirpated. 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.
Few contraindications exist to treating renal AVMs. Contrast allergy may necessitate premedication with antihistamines and steroids. Otherwise, embolization of renal 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 (GFR) of 10-15%, which may keep many patients from needing dialysis for end-stage renal disease (ESRD). However, ultrafiltration injury may occur when less than 25% of the total renal mass is spared.
Thus, in patients with solitary kidneys, bilateral 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 AVMs, in all patients when technically feasible. This serves to protect patients from the small risk of developing renal insufficiency in the future.
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 AVMs. Hematuria often improves with bedrest. Analgesics may be necessary.
Little is known about the natural history of untreated AVMs. Acquired arteriovenous fistulas (AVFs) tend to resolve spontaneously. One report described spontaneous resolution of an 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 AVM or the development of irreversible hypertension. Because patients with 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 AVM. Finally, renal failure can occur as a complication of the contrast agents used during radiographic evaluation.
The initial therapy for treatment of AVMs is usually angiographically guided embolization of the malformation. Numerous substances have been injected in an effort to ablate the AVM. Initial attempts at embolization were complicated by recurrence of the 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 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.
Superselective embolization with coils and microspheres has also been described. Care must be taken with coils to avoid migration beyond the AVM, which could lead to the potential for pulmonary embolism. Superselective embolization has not been shown to cause any adverse effect on renal function.
Uchikawa et al described successful use of glue embolization with the double coaxial microcatheter technique to treat renal AVMs with multiple tortuous feeding arteries.
Repeat treatments may be needed to completely ablate the 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 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 (IV) 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.
The treatment most likely to cure an AVM is total nephrectomy. Total nephrectomy is indicated for large cirsoid 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 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 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 AVMs.
In addition to partial nephrectomy, other techniques have been used to treat renal 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 AVMs, surgical intervention is usually reserved for those cases refractory to embolization or those associated with malignancy.
The successful treatment of renal AVMs relies on definitive localization of the lesion. Meticulous radiographic evaluation is needed because some lesions are subtle.
Medical conditions, especially 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 in 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 through inadequate perfusion. Pharmacologic 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 GFRs and split renal function. These objective data can help accurately guide the need for nephron-sparing surgery (eg, partial nephrectomy).
Total or simple nephrectomy to treat renal 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, 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 ultrasonography provides the means to localize small lesions.
Routine postoperative care is indicated after nephrectomy, as are careful hydration and close hemodynamic monitoring. Aggressive pulmonary toilet is essential. Early ambulation is important, and activity restrictions after partial nephrectomy are becoming less stringent. Resumption of diet is influenced mostly by surgeon bias, though caution is warranted following transabdominal approaches. The influence of CHF can complicate the response to nephrectomy. In patients with AVM-induced heart failure, intensive monitoring, including pulmonary artery catheterization, may be needed.
Potential complications of nephrectomy can be classified by organ system, as follows:
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 to the treatment of renal AVM has not been well described.
If the contralateral kidney is normal, renal function is usually normal postoperatively, though increased blood loss, longer duration of the operation, and reperfusion effects may rarely cause total renal impairment after partial nephrectomy.
Urinary fistulas and AVFs 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. AVFs may be silent, discovered incidentally during subsequent imaging studies. They also may manifest with signs or symptoms similar to the original 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 case description noted coil and guide-wire 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 the femoral artery) are not uncommon, with clinical evidence of hematoma occurring in approximately 5% of patients.
Individualized follow-up care is necessary after intervention. Unless total nephrectomy is performed, recurrence is possible. Additionally, hypertension and renal function should be assessed. Routine imaging is not usually indicated.
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.