Renal Arteriovenous Malformation Workup

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

Approach Considerations

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 adopted as an alternative to iodinated and gadolinium-based contrast imaging. Its use in diagnosing renal arteriovenous fistula (AVF) after renal biopsy has been described. [7] 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. [8]

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Laboratory Studies

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 [PT], activated partial thromboplastin time [aPTT], 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.

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Imaging Studies

The initial diagnostic evaluation of hematuria is debatable. No single study detects all pathologies. Renal ultrasonography (US) has been advocated as an ideal initial study because it 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 gained 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, US, and CT are described below.

Intravenous pyelography

The advantages of IVP in this setting include obtaining anatomic detail (especially of the collecting system) and functional information about perfusion, function, and obstruction. The disadvantages include cost, exposure to radiation and contrast agents, 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.

Doppler ultrasonography

US has gained favor as a noninvasive means for evaluating renal causes of hematuria. Discussion of the debate regarding the relative merits of US and IVP for this purpose is beyond the scope of this article.

US is more sensitive for the detection of small renal masses and can help distinguish more reliably between cystic and solid masses. However, renal US is less accurate for identifying lesions of the collecting system and provides only indirect information about renal function.

Doppler US has increased 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, US may not be able to help distinguish AVMs from small solid masses.

Computed tomography

Further evaluation of renal lesions detected by means of US 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 conge 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 angiogra Same patient as in the previous image; CT angiogram on coronal image illustrating a prominent left arteriovenous malformation (AVM) with aneurysmal renal vein.

Angiography

Angiography remains the criterion standard for the clinical diagnosis of AVM. Additionally, angiography provides the means for treatment with transcatheter embolization. [9] (See the image below.)

Arteriogram demonstrating large right renal arteri 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.

Magnetic resonance angiography

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. [10] (See the image below.)

MRA reconstruction of the same patient. MRA reconstruction of the same patient.
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Procedures

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.

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Histologic Findings

One study found that the microscopic features of AVMs were histologically identical to those of 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. [1]

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