Woman on chronic hemodialysis.
Which of the following choices likely apply? Please respond with TRUE or FALSE.
The most common cause of arteriovenous fistula dysfunction is outflow stenosis (that is, narrowing within venous portion of the fistula). Stenosis may itself cause diminished flow; the resultant stasis may contribute to subsequent thrombosis, severely limiting fistula patency. Thus, percutaneous correction of stenosis plays an important role in maintaining viability of AV fistulas.
AV fistula stenosis is thought to arise from neointimal hyperplasia caused by intimal injury. The intimal injury may be mechanical (e.g. repeated needle punctures) or metabolic (e.g. uremia). The final common pathway for intimal injury is the creation of oxygen free radicals and mediators that promote the ingrowth of smooth muscle, extracellular matrix, and inflammatory cells. Stenosis may either prevent the maturation of a newly created fistula, or complicate an already matured fistula.
Radiologic overview of the diagnosis:
When a patient presents with a malfunctioning dialysis fistula, the work-up begins with a review of previous imaging and history of previous fistulaplasty. On physical exam, diminished thrill with or without pulsatile flow is suspicious for decreased fistula patency. The fistula may be visualized under ultrasound to better target the areas of interest, and to assist with obtaining vascular access.
Malfunctioning dialysis fistulas are traditionally evaluated with a procedure called a fistulagram. The patient is placed on the operating table and prepped in sterile fashion. A micropuncture set is used to obtain intravascular access to the fistula, usually in a retrograde direction (that is, from the venous end towards the anastomosis). Digital subtraction angiography is subsequently performed under rapid bolus administration. Stenosis, thrombus, aneurysm, or other abnormalities are identified. Usually, treatment for abnormalities is performed at the time of fistulagram. Angioplasty is the first-line treatment for stenosis, with stenting reserved for troublesome lesions refractory to ballooning. "Significant" stenosis requiring treatment is generally considered to be luminal narrowing of 50% or more, with questionable benefit for correcting less severe narrowing.
The main differential consideration is catheter-based vasospasm. Unlike stenosis, vasospasm often resolves after several minutes, particularly after the administration of nitroglycerin. Either mural or loose thrombus may also cause luminal filling defects, but are less likely to form a discernible vessel "neck".
CT angiography has diagnostic sensitivity and specificity comparable to fistulagram for detection of AV fistula stenosis. Because the conventional fistulagram provides an opportunity for immediate angioplasty, however, it remains the workhorse of percutaneous AV fistula maintenance.