Renal Arteriovenous Malformation Treatment & Management

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.^[7] Superselective embolization with coils and microspheres has also been described. 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).

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.

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.

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.

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.

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, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Blood in the Urine.

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.

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.^[8]

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.

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.