Renal Arteriovenous Malformation Treatment & Management

Updated: May 10, 2018
  • Author: Mark R Wakefield, MD; Chief Editor: Vincent Lopez Rowe, MD  more...
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Treatment

Approach Considerations

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 at preoperatively determining 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. [11]

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 for 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.

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Nonoperative 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 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. [12, 13] 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. [14]

Superselective embolization with coils and microspheres has also been described. [15] 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 have any adverse effect on renal function.

Cyanoacrylate has been employed for embolization as well. [16] Uchikawa et al described successful use of glue embolization with the double coaxial microcatheter technique to treat renal AVMs with multiple tortuous feeding arteries. [17]

Repeat treatments may be needed to ablate the AVM completely. 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. [18]

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Surgical Therapy

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 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.

Preparation for surgery

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).

Operative details

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 ischemic time should be limited 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.

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Postoperative Care

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.

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Complications

Complications of surgery

Potential complications of nephrectomy can be classified by organ system, as follows:

  • 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 (GI) complications include ileus, pancreatitis, and duodenal injury (from retractor tension)
  • Neurologic complications include subcostal nerve injury and stroke
  • Infections, though uncommon, may include Foley catheter-induced cystitis, incisional sepsis, and pneumonia

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 of embolization

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. [19] 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.

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Long-Term Monitoring

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.

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