“Distinguishing between ‘good’ aneurysms, and ‘bad’ aneurysms – five signs”
In my previous post (May 23rd), I stated that most aneurysmal fistulas, though overgrown and perhaps startling, are not dangerous and can continue to be cannulated for dialysis. It goes without saying, though, that they draw attention and suspicion. In an extreme case, a patient with a wrist fistula dating back to 2001, comes to have his fistula evaluated each time he gets a new nephrologist because the thing is just so big. It has been stable and problem free for the last nine years, and the patient has consistently expressed a desire to leave well enough alone (images 1-3).
"Aneurysms – danger signs", image #1 – An eight-year-old fistula
The patient had a wrist fistula created in 2000, and came for evaluation, saying “I got a new nephrologist, and she wanted me to get it checked out”. It was soft, non tender, and though the skin was scarred, it was healthy and moved easily over the fistula. He denied recent growth, pain, or any functional problems, and wanted to avoid unnecessary surgery.
"Aneurysms – danger signs", image #2 – two years later - 2010
Once again, the patient had a new nephrologist, and sent the patient “to get it checked out”. It was soft, non tender, and essentially unchanged from two years previous. And once again, the patient was offered an aneurysmoplasty but declined.
"Aneurysms – danger signs", image #3 - 2016
Same old story, new nephrologist, return to the surgeon. As you can see, the fistula is essentially unchanged over a eight year period, and without any functional problems. The patient declined any intervention.
"Aneurysms – danger signs", image #4
This actually a pseudoaneurysm, created during venoplasty of a superficialization swing zone stenosis, and which began growing rapidly. This example actually contains the classic three danger signs – rapid growth, local tenderness, and skin compromise. High risk for rupture and infection.
"Aneurysms – danger signs", image #5
This is a partial thickness ulceration over an aneurysmal fistula. It has the potential to heal if not further traumatized and if not complicated by elevated access pressures. If the fistula is soft, I might prohibit use of that segment and let it heal. If the access is high-pressure and pulsatile, the risk of further breakdown is increased, and the potential for bleeding as well, buying the patient an urgent trip to the OR. In that case an outflow venoplasty or stenting can lower the access pressure and risk, and it is an easy measure to make an elliptical skin incision around the defect, perform a partial skeletonization of the damaged segment, and wedge it out with a local repair without interrupting the blood flow. The normal skin is then closed over the repair, and the segment returned to use in several weeks.
"Aneurysms – danger signs", image #6
This is a full thickness defect over an aneurysmal fistula. It does not have much potential to heal, because the defect goes all the way through to the lumen. If the fibrin plug comes out, the patient may well bleed to death. We were sent such a patient from an access center that had failed to recanalize a central stenosis turned occlusion that they had been managing for several years (Thank you very much!). We took one look at this, and told the patient to go directly to the ER for an urgent repair. She decided to go home first, and blew on the way from her house to the hospital. After getting CPR in the street, spending three weeks in the ICU, and getting multiple units of blood transfusion, she ultimately lost the fistula. She was lucky to survive.
"Aneurysms – danger signs", images #7 and 8
This limited zone of cannulation has obviously created skin damage and inflammation, but is it dangerous? The “pinch test” shows that the skin is intact and pliable, and is not fused to the underlying fistula. There is an intervening layer of subcutaneous tissue, and like a double hulled boat, the two layers provide added protection against complete breakdown and bleeding. In this case, we advise moving the zone of cannulation, and letting this area heal, plus scheduling a fistulogram and venoplasty if the access is pulsatile or the venous pressures high on dialysis.
"Aneurysms – danger signs", images #9, 10 and 11
Cephalic arch stenosis is the most common cause of access pulsatility and elevated venous pressures in brachiocephalic fistulas, and as such contributes to aneurysmal changes. The most common expedient is repeated dilation as needed to lower pressures, or stenting, or much less frequently, a revision diverting the flow to the brachio-axillary vein in the upper arm.
"Aneurysms – danger signs", images #12, 13 and 14
“Transposition swing zone” stenosis is the most common cause of access pulsatility and elevated venous pressures in transposed basilic fistulas, and as such also contributes to aneurysmal changes. The most common expedient is repeated dilation as needed to lower pressures or stenting. Obviously, in retrospect I wish I had put in a larger diameter stent.
"Aneurysms – danger signs", images #15, and 16
“Access pulsatility” and elevated venous pressures are not always due to outflow stenosis. In this case, a wide open anastomosis (left side) converts the fistula to an extension of the brachial artery (see the post “Firehose fistulas”). The unchecked arterial pressures are much higher than they should be (ideally, the mean intraaccess pressure should be less than 40% of the mean arterial pressure), and I have seen flows up to five liters a minute. These pressures and flows accelerate aneurysmal changes and potentiate the formation of pseudoaneurysms. High pressure and high flow fistulas are obviously dangerous, since any bleeder can be hard to control, and any major breach in an access carrying three to five liters a minute can lead to exsanguination very quickly. The remedy is to reduce the inflow, and thus the pressure (right side – after inflow banding).
"Aneurysms – danger signs", image #17
This is a great example of a dilated feeding artery (nearly a centimeter in diameter), and a wide open anastomosis converting this fistula into a virtual extension of the aorta. In this case, the flow was approximately four liters a minute. Note that the artery distal to the anastomosis quickly tapers down to a more normal size.
The complication of aneurysms most feared is the risk of rupture. This is actually much rarer in aneurysms than pseudoaneurysms (see the May 23rd post for an explanation of the difference between these). The risk of rupture is very low in either in the absence of the three factors we have cited over the years, plus two others we have added recently to comprise “The five danger signs”.
The first danger sign is rapid growth. It stands to reason that anything that grows bigger every day is bound to be a problem. Aneurysmal fistulas tend to have thickened walls and to be stable, while pseudoaneurysms are essentially contained ruptures outside the walls of the original conduit, and can grow rapidly if there is nothing besides subcutaneous fatty tissue and skin to restrain them. I saw one woman with a pseudoaneurysm that had appeared in the upper arm after a venoplasty, and I scheduled her for a revision the next Monday. Friday evening she called me and said, “My bump turned into a cone” (Image #4), so we brought her in and repaired it that night.
The second danger sign is local tenderness, caused by the tearing effects of a rapidly expanding mass (like a pulsatile pseudoaneurysm), or infiltration of blood into the tissues from a rupture under the skin, from the inflammatory effects of a clot in the aneurysm or pseudoaneurysm, or from a localized infection (again, image#4). Thrombosis in a vessel is inflammatory, and if that is all it is, can be treated symptomatically with the expectation that it will pass, but all the other possibilities are dire, so a painful lump should not be ignored until it is evaluated by ultrasound.
The third classic sign is skin compromise, ranging from skin that has become ischemic from being stretched over an expanding mass until it becomes devascularized (see image #4, and the darkened area at the peak of the “cone”), to partial thickness skin ulceration (image #5), or a frank skin defect. Some of these lesions progress to the point that there is only a fibrin plug jammed into a full thickness hole in the fistula (image #6). If the plug becomes loosened on one edge it bleeds and is typically taped down tightly until it seals up again. If it pops out completely, the bleeding is intense and difficult to control, because a new “plug” takes time to form.
Our fourth sign is persistence of a normal separation of skin and fistula by a layer of subcutaneous tissue (Images #7 and 8). If these two separate layers exist and are not fused together, the risk of precipitous bleeding is much reduced. It also indicates that the damaged skin can heal if cannulation practices change.
The fifth sign is access pulsatility. Elevated pressures in an access contribute to excessive bleeding after decannulation, infiltration, conversion of a puncture into a laceration, conversion of a laceration into a pseudoaneurysm, and ultimately rupture of the pseudoaneurysm. Reducing intraaccess pressure reduces the incidence and progression of all of these undesirable changes.
Historically, we have focused on outflow stenosis. Reducing outflow resistance increases flow, and reduces intraaccess pressure. There are stereotypical stenoses common in each kind of fistula. In the brachiocephalic fistulas, (1) the narrowing below the first lateral branch, (2) a stenosis at the junction of middle and upper thirds of the fistula associated with a valve and common second lateral branch, and (3) in the cephalic arch, where the cephalic vein curves down behind the upper edge of the pectoralis major muscle to join the axillary vein, gathers in and gives off branches and contains several valves, are common. The cephalic arch stenosis is the most common lesion causing elevated venous pressures and access pulsatility in a brachiocephalic fistula (Images #9, 10 and 11).
In a transposed basilic fistula, the “swing-zone” where the vein transitions from its natural position in the medial arm to the segment brought up to the skin and transposed anteriorly, is particularly vulnerable to stenoses (Images #12, 13 and 14).
To complicate things even further, elevated pressures and pulsatility may no0t be due to outflow problems, but to excessive flows coming into the fistula from overlarge feeding arteries and wide open anastomoses (Images #15 and 16, and image #17). Controlling the inflow volume and pressure may be necessary if one is to reduce the risk of rupture and bleeding from an aneurysmal fistula.
Evaluation and successful management of aneurysmal fistulas are more complicated than most people think. Combined open and endovascular techniques may need to be applied together, and the ability to measure flows is very helpful. But again, all aneurysms are not dangerous, and an understanding of these factors will allow you to assess the situation more accurately.
Next post – “Complications of aneurysms other than bleeding”
