Cool! I am awake later than Marc Webb!

Fix it ! It looks like it's getting ready to blow.

But seriously. I would resect this and do it in some way that preserves the access if possible.

Dr. Gabbard - I was up with a ruptured right innominant vein, a hemothorax, and case of DIC with d-dimer level over 6 thousand - you might have been up later than me, or not. Either way, it is kind of you to think of me - thanks!
About your question - aneurysms of fistulas are common, and usually not a terrible risk. We monitor them, track them with serial photos, fix them with aneurysmoplasty if they are a size problem, resect and rearterialze them for flow reduction in "firehose" fistulas. We say that if they are stable and low pressure, they should not be an urgent problem. If the skin is freely movable over the fistula it is less concerning. Rapid growth, local pain, and skin compromise mandate intervention.
usually an outflow venoplasty to reduce pressure, and a revision.
However, this looks like a pseudoaneurysm, and the skin looks compromised. I would send the patient straight to the ER for a urgent resection, with or without a fistulogram and venoplasty. One such patient decided to go home for some personal items instead of going directly to the ER. She blew on the way, lost control of the vehicle and crashed, was coded in the street, and re-bled in the ICU after she got her pressure back - she lost the fistula, but was lucky enough to live.

Dr. Webb.... You comments almost always make me chuckle. You also have a good eye. This patient did have a pseudoaneurysm. This was a large, thrombosed one. The ventral surface of the fistula was completely open. After resecting the pseudoaneurysm, we were able to close the vein. The biggest problem was that the defect was a bit difficult to close. I learned that the skin on the sides of the pseudoaneurysm is more viable than it appears. Next time, I will resect the pseudoaneurysm leaving more skin from the wall of the out-pouching defect. We also performed an angiogram with stenting of the cephalic arch and vein due to poor response from angioplasty. I have more pictures to show the resection of the lesion. I cannot post the follow up pictures. The ASDIN helpers can post them for me.

Assuming good transplant function. ligate and excise. Wouldn't waste time or money trying to keep this one going. If renal fxn poor (Cr > 2.5 and deteriorating), I'd come up w/ a different plan.