Renal Arteriovenous Malformation Workup

• In general, the laboratory evaluation is dictated by the clinical presentation of the patient.
• Hemoglobin/hematocrit

  • Anemia may contribute to the severity of heart failure in some patients with renal arteriovenous malformations (AVMs).
  • Further, significant hemorrhage and hemodynamic instability are associated with arteriovenous malformations (AVMs). In these cases, frequent assessment of the hemoglobin and hematocrit values is indicated.
• Chemistry assay

  • 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 >65 y, 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, bleeding time)

  • Coagulopathies may be responsible for bleeding that reveals the presence of an arteriovenous malformation (AVM).
  • Bleeding disorders should be corrected before most interventions are pursued.
• Type and crossmatch blood: The availability of crossmatched blood becomes important in hemodynamically unstable patients.
• Renal vein renin test - A way to test for renovascular hypertension

  • Radiology places a catheter in the groin area at the femoral vein
  • 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
• Urinalysis/urine culture

  • Rarely, renal arteriovenous malformations (AVMs) may be discovered during the evaluation of microscopic hematuria.
  • Urinary tract infections should be excluded before intervention is pursued.

• Choice of imaging study

  • The initial diagnostic evaluation of hematuria is debatable. No single study detects all pathologies.
  • Renal ultrasound has been advocated as an ideal initial study because renal ultrasound is noninvasive, relatively inexpensive, and helps to detect many lesions.
  • Until recently, most urologists favored the use of intravenous pyelography (IVP) for the initial evaluation of patients with hematuria.
  • CT scans are 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 arteriovenous malformations (AVMs) on IVP, ultrasound, and CT scan images are described.
• Intravenous pyelography

  • The advantages 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.
  • Arteriovenous malformations (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 arteriovenous malformation (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 arteriovenous malformation (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 arteriovenous malformation (AVM).
• Doppler ultrasound

  • Ultrasound has recently gained favor as a noninvasive means for evaluating renal causes of hematuria. The debate about the merits of ultrasound versus IVP for this purpose is beyond the scope of this article.
  • Ultrasound is more sensitive for the detection of small renal masses and can help distinguish more reliably between cystic and solid masses. However, renal ultrasound 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 arteriovenous malformation (AVM) by the use of color-duplex Doppler ultrasound studies. The lesions were identified as arteriovenous malformations (AVMs) based on the turbulent blood flow within a cystic mass. Otherwise, ultrasound may not be able to help distinguish arteriovenous malformations (AVMs) from small solid masses.
• Computed tomography

  • Further evaluation of renal lesions detected using ultrasound or IVP usually includes CT scans 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 arteriovenous malformations (AVMs).
  • CT urography has replaced IVP in some centers for the initial evaluation of hematuria. With proper equipment and oversight, CT urography, angiography, or both can provide information about renal function, as well as detailed definition of the anatomy, including the vascular and collecting systems. As such, CT angiography has replaced traditional angiography for many indications, including evaluation of the living kidney donor and preoperative planning for complex partial nephrectomy.
• Magnetic resonance angiography

  • MRA is a promising technology for the evaluation of renal masses.
  • MRA 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 arteriovenous malformation (AVM).

• Urine cytology: This is usually performed during the evaluation of hematuria, although it does not specifically contribute to the diagnosis of a renal arteriovenous malformation (AVM).

• Angiography

  • Angiography remains the criterion standard for the clinical diagnosis of arteriovenous malformation (AVM). Additionally, angiography provides the means for treatment with transcatheter embolization.
  • Angiography of an arteriovenous malformation (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 arteriovenous malformation (AVM). The actual malformation may be a subtle blush if the arteriovenous malformation (AVM) is small, or the multiple small tortuous vessels may be easily visualized. Cirsoid arteriovenous malformations (AVMs) are supplied by multiple arteries, while the cavernous arteriovenous malformations (AVMs) and arteriovenous fistulas tend to be supplied by single vessels.
• Cystoscopy

  • Because most patients with arteriovenous malformations (AVMs) present with hematuria, cystoscopy should be performed to evaluate for coincidental lower tract pathology.
  • Cytologic evaluation of the urine is also useful for screening for carcinoma in situ of the bladder, which can be missed during diagnostic cystoscopy.

A recent 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.^[4]