The Geometry of Parallel Grafts in the Iliac Arteries

The development of metachronous common iliac artery aneurysm, or progression of them, after prior treatment with EVAR (endovascular aneurysm repair), particularly with “bell bottoming” is typically treated with coil embolization of the internal iliac artery and extension of the stent graft into the external iliac artery. While CH-EVAR has been in the news with the recent results from the PERICLES registry, I have never been entirely convinced of its durability. That is different in the case of building parallel grafts in an iliac limb of an EVAR graft (reference).

Here, the geometries, thrombosis, and forces combine to make gutter flow and endoleak unlikely. Choosing the right size of stent grafts to channel to the external and internal iliacs seems to be a challenge, but is easily solved by this scheme -which I can’t claim as my own, but was thought up by a surgeon in upstate New York who choses to remain anonymous.*

The diameter of the stent graft to be sealed to is measured and an area calculated. The sum of the areas of the two grafts to be placed need to equal or slightly exceed the area of this inflow stent graft. If you have decided the size of the external iliac graft, for example, then the diameter of other graft is merely a few geometric formulas away.

Here is a table that can be helpful in avoiding those formulas.
diameter area table.jpegThe inflow graft area is taken from its measured diameter. Then usually one or the other artery has an obligate size -a size the graft has to be while the other has more “wiggle room.” The other thing that comes from experience is that the AFX graft’s iliac limb extension don’t get the B-infolding that can affect an oversized stent graft placed in a small artery and it accomodates a neighbor well.measurement_3

For example, take this patient who after EVAR of aortic aneurysm with AFX developed metachronous dilatation of the common iliac artery to 3.9cm with abdominal pain. The average diameter is 18.5mm. From the table, that rounds to 19mm corresponding to 283.53 square mm. If the internal iliac artery requires a 13mm graft, that is 132.73 square mm, the difference being 150.80 square mm. That corresponds to a 14mm diameter graft, but a slightly larger graft is preferred for oversizing. The external iliac artery is 8mm, and putting a 13mm Viabahn (largest available) in that would result in the B-infolding in the 8mm external iliac. Here, I bailed myself out by simply placing a 20mm AFX iliac limb extension, which by virtue of its design is resistent to infolding and tolerant of parallel grafts laid alongside in constricted channels. I found that the AFX iliac limb, a 20-13mm x 88mm length extension well suited for this.

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The AFX graft limb seems to adapt to the presence of the parallel “sandwich” graft which is deployed second and ballooned last. In followup, there was shrinkage of the common iliac artery aneurysm sac and no endoleak.

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Compared to my other parallel graft case treating a metachronous saccular common iliac aneurysm years after an EVAR with a Gore endograft (link), which by table calculation, resulted in 8% oversize in calculated areas, this particular technique with a large AFX graft and an appropriately sized Viabahn seemed to work well the setting of a previously placed AFX graft. It allows one to avoid hypogastric occlusion.

The final option of a femoral or external iliac to internal iliac bypass after extension across the bifurcation to the external iliac artery is still a reasonable choice, although it seems to be receding into history.

Reference

Smith, Mitchell T. et al. “Preservation of Internal Iliac Arterial Flow during Endovascular Aortic Aneurysm Repair Using the ‘Sandwich’ Technique.” Seminars in Interventional Radiology 30.1 (2013): 82–86. PMC. Web. 9 Dec. 2016.

*While these grafts are not FDA approved for use in this manner, many times, with a prior endograft or graft in place, using the currently available and approved Gore Iliac Branch Endoprosthesis (IBE) in this common scenario would still be off label usage of an approved device, and only if it is feasible, which most times is not. For nonmedical readers, many commonly available devices and medications are used off-label, such as aspirin for blood thinning.

When good enough is better than perfect: a case of end stage visceral segment aortic occlusive disease

The patient is a woman in her 60’s who self referred for complaint of abdominal pain, weight loss, and rest pain of the lower extremities. She is a 40 pack year smoker and had severe COPD, hypertension, congestive heart failure with mitral regurgitation, chronic kidney disease stage IV, and ischemic rest pain of the legs. She had a 30 pound weight loss due to severe postprandial abdominal pain. She had bloody stools. Her kidney function was worsening, and dialysis was being planned for likely renal failure but she was against dialysis. She had consulted several regional centers but was felt to be too high risk for surgery and with her refusal of dialysis, would be a high risk for renal failure and death with intervention. Physical examination revealed weakened upper extremity pulses, and nonpalpable lower extremity pulses and a tender abdomen. In clinic, she developed hypoxia and dyspnea and was admitted directly to the ICU.

preop-cta

CTA (above) revealed severely calcified atherosclerotic plaque of her visceral segment aorta occluding flow to her mesenteric and renal arteries and to her leg. The right kidney was atrophic. The left kidney had a prior stent which looked crushed. The infrarenal aorta was severely diseased but patent and there were patent aortic and bilateral iliac stents.

Echocardiography revealed a normal ejection fraction of 60%, diastolic failure,  +2 to+3 mitral regurgitation, and pulmonary artery hypertension. She did respond to diuresis and stabilized in the ICU. Intervention was planned.

Options that I considered were an extranatomic bypass to her legs and revascularization from below. I have come across reports of axillo-mesenteric bypass, and I have performed ascending and descending thoracic aorta to distal bypass for severe disease, but concluded, as did the outside centers, that she was a formidable operative risk. Also, there was a high likelihood of great vessel occlusive disease. Looking at her CTA, I felt that she needed just a little improvement in flow -not perfect but good enough. The analogy is like drilling an airline through a cave-in. Also, her left kidney gave a clue -it was normal sized and survived the stress test of a contrast bolus for the CTA without dying. A discussion with the patient green lighted an attempt -she understood the cost of failure but did not wish to linger with this abdominal pain.

Access for intervention was via the left brachial artery. Aortography showed the severe stenosis at the origin of the SMA and the nearly occlusive plaque in the visceral segment aorta.

preintervention-aortogram

The plaque was typical of the coral reef type, and had an eccentric channel that allowed passage of a Glidewire. Access into the left renal artery was achieved. Its stent was patent but proximally and distally there were stenoses; this was treated with a balloon expandable stent. The path to it was opened with a balloon expandable stent to 8 mm from femoral access. This was the improvement the renal needed. A large nitinol stent was placed from this access in the infrarenal aorta when severe disease above the iliac stents was encountered.  The SMA was then accessed and treated with a bare metal stent.

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Renal stent was reaccessed and ballooned in this pentultimate angiogram

Her creatinine improved, as did her intestinal angina. She was discharged home. She later returned a month after the procedure with complaints of nausea and vomiting and right lower quadrant abdominal pain and was discovered to have an ischemic stricture of her small bowel. This was removed laparoscopically and she recovered well. She recovered her lost weight and now a year and a half later, remains patent and symptom free.

Discussion: Dr. Jack Wiley includes in the preface to his atlas of vascular surgery the words of Dr. Joao Cid Dos Santos, the pioneer of endarterectomy techniques, “Vascular surgery is the surgery of ruins.” And in that context, good enough is sufficient.

 

3D VR Images from CT Data Very Useful in Open Surgical Planning: Popliteal Venous Aneurysm

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Patient is a middle aged man with history of DVT and PE who in preoperative workup for another operation was found to have a popliteal venous aneurysm affecting his right leg. Unlike the recently posted case (link) which was fusiform, this aneurysm was saccular (CT above, duplex below). Popliteal venous aneurysms have a high risk of pulmonary embolism because: they tend to form clot in areas of sluggish flow and once loaded with clot, will eject it when compressed during knee flexion.

preop-duplex

When I perform open vascular surgery, I tend to get a CTA not just because it is minimally invasive and convenient, but because it gives important information for operative planning. The volume rendering function, which takes the 3 dimensional data set from a spiral CT scan, and creates voxels (3 dimensional pixels) of density information and creates stunning images such as the one featured on the current September 2016 issue of the Journal of Vascular Surgery. But these are not just pretty pictures.

In fact, I use these images to plan open surgery, even to the location of incisions. Vital structures are seen in 3D and injuries are avoided. Take for example the CT Venogram on the panel below. By adjusting the window level, you have first the venographic information showing the saccular popliteal venous aneurysm on the left panel, you can also see where it is in reference to the muscles in the popliteal fossa. The greater saphenous vein and varicose veins below are well seen.

ct-3dvr-planning

By adjusting the level, subcutaneous structures are better seen including the small saphenous vein which could be harvested to create a patch or a panel graft from a posterior approach. A final adjustment of the window level on the right shows the skin, and I can now plan the curvilinear incision.

By changing the orientation, I can also recreate the surgeon’s eye view of the leg in the prone position (below).

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And you can see how well it matches up to the actual operation shown below:

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This was treated with plication of the saccular aneurysm and unlike the fusiform aneurysm, I did not sew over a mandrill (a large 24F foley) inserted through a transverse venotomy, but rather ran a Blalock type stitch under and over a clamp.

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The several weeks postoperatively showed no further trace of the saccular aneurysm.

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The volume rendering software grew out of the 3D gaming industry. The voxel data that paints flesh and bone on skeletons and costumes and weapons is far more complex than what is applied for the 3DVR packages that are available. The images shown for this post comes from TeraRecon/Aquarius, but they are also available as open source software from Osirix, Vitrea, and various software packages sold with CT scanners. While those that are tied to the scanners are often tied to dedicated workstations -limiting you to going to Radiology and taking over their workstation, many will work in the cloud for both the DICOM data and for virtual desktop access through mobile. Contrast is not necessary if the patient has kidney dysfunction -the vessels can be manually centerlined -ie. a line can be dropped in the center of the artery to illustrate its course when viewing the VR images.

I will plan the surgery while in the clinic with the patient, actually tracing out the incisions and dissections necessary to achieve success. It is a wonderful teaching tool for trainees. But most critically, it helps me imagine the operation and its successful completion.

Dysphagia Lusoria -a simplified approach

Arrow points to the esophagus. Tension is maintained by the tether on either side of the esophagus. By releasing one side, the tension is relieved.

The patient had been suffering with dysphagia for over a decade and had had extensive head and neck work up which found a goiter. Medical treatment of this goiter failed to relieve the lingering sensation of food getting stuck and the constant feelingof choking. It was only after a search for mediastinal sources of dysphagia that an aberrant right subclavian artery was found. 


One of the advantages of working at the Clinics (I was a fellow at the Mayo, and currently on staff the the Cleveland) is that the infrequent is common while the common is rare. Recently in clinic, I had not one but two patients with dysphagia lusoria. It was the observation of Dan Clair’s,  chairman emeritus, that by simply transposing the aberrant and yet nonaneurysmal right subclavian artery, the tension on the esophagus and trachea are relieved. Or as the dictum might go: it takes two hands to garrote someone


The question is then what to do with the stump? The natural history of the untreated stump is unknown but may be more benign than one might assume. It certainly doesn’t degenerate into an aneurysm all the time -chest CT’s are fairly common and when these are discovered, they are not usually aneurysmal like persistent sciatic arteries which present typically as aneurysms with thromboembolism. Perhaps because we don’t sit on the subclavian artery as we would on a persistent sciatic artery that these aberrant right subclavian arteries don’t degenerate. 


The old fashioned way I learned to treat these aneurysms (Kommerell Diverticula) was through a high thoracotomy and short graft repair of the aorta, replacing the origin of the diverticulum.  This is a dangerous operation for  an older, sicker, and often cachectic patient. The more recent reports involve a left carotid subclavian bypass or transposition and TEVAR after a right carotid subclavian revascularization. This second step may be unecessary if the non-aneurysmal stump proves to be benign. I don’t recommend coil embolization of the stump as mass effect of packed coils adjacent to the esophagus can cause dysphagia to recur, and this may necessitate an open resection and repair (observation, DC). 

The patient underwent a successful right carotid subclavian transposition and had immediate relief of her dysphagia for the first time in over a decade, especially because she had been told she may have been imagining the discomfort. Kudos to her physicians who ordered the CT of the chest that discovered her arch anomaly. Follow up at 6 weeks showed a stable subclavian stump and patent transposition (images above). My plan is for regular interval CT’s with increasing intervals as time passes. 

Reversing paralysis with a bypass

Dissection CTA

The patient is middle aged and had a type B thoracic aortic dissection (TBAD) as a consequence of recreational substances that acutely raised his blood pressure. At the outside hospital, he had a CTA showing the dissection extending from his left subclavian artery and causing occlusion of his superior mesenteric artery (SMA). He developed abdominal pain and was swiftly transported to our acute aortic syndrome unit. He was taken to the operating room and underwent a TEVAR of the dissection and stenting of his SMA -this is similar to other cases I have discussed in prior posts so I am omitting the technical details. The stent covered the left subclavian artery origin to exclude the origin of the dissection. The stent was extended to the distal thoracic aorta but did not go to the celiac origin. 

TBAD post stent

Post procedure, his lactate never rose and he was maintained on the usual post procedure protocol of keeping MAP’s (mean arterial pressure) above 80mmHg. His left subclavian artery was covered but I do not routinely bypass, especially when the left vertebral artery is at least equal in size to the contralateral one. I don’t often place spinal drains for urgent/emergent cases particularly in patients who have never had infrarenal aortic surgery and patent hypogastric arteries. He was kept sedated overnight and awoke in the morning unable to move his legs to command. He had no pain sensation up to his umbilicus.

A spinal drain was emergently placed and his blood pressure was raised to MAPs of 90+, but these failed to reverse his paralysis. After discussion among my world class partners, I chose to take the patient back for a carotid subclavian bypass which was done through a single incision with a dacron bypass graft.

Carotid subclavian bypass CTA

His paralysis resolved. He was discharged home, ambulating without assistance. Spinal cord complications are reported to occur between 1-5 percent of patients undergoing TEVAR for complicated TBAD. They were seen in 2 of 72 patients in the TEVAR arm of the INSTEAD trial (Circulation, 2009 vol. 120(25) pp. 2519-28), and was permanent in 1. While there are some who routinely place prophylactic drains, it is unclear to me that they have a significant effect if placed unselectively. I will place a Preop drain in the instance of infra renal graft, hypogastric arterial occlusive disease. In the instance of a dominant left vertebral, I will perform concomitant bypass, but just as often not. This is a gratifying and rare outcome of paralysis reversed with a carotid subclavian bypass when spinal drain and permissive hypertension did not. 

Never Stop Following Stent Grafts -Type IV endoleak causing slow growth in 12 year old stent graft

Centerline

 

The patient had undergone EVAR for bilateral common iliac artery aneurysm with the original Gore Excluder stent graft a dozen years before with coil embolization and extension to the external iliac on the larger side and femoral to internal iliac artery bypass on the other side. A coagulopathy, one of the clotting factor deficiencies, had made him high risk for bleeding with major open surgery. His aneurysms never shrank but remained stable and without visible endoleak by CT for a long time resulting in ever longer intervals between followup.

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2013

Between 2009 and 2013, there was subtle enlargement on the embolized side without a type I or type III leak, and the patient was brought back a year and a half later, with further growth of the sac.

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2015

This was a relatively rare type IV endoleak that was causing sac enlargement due to excessive graft porosity of the original Excluder’s graft material. Its treatment is either explantation or relining. We chose to reline the graft with an Excluder aortic cuff at the top and two Excluder iliac limbs.

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This was done percutaneously and in short followup, there has been stabilization and even some reduction in the aneurysm circumference.

CT Scans

 

It was long known that a certain percentage of PTFE grafts “back in the day” would sweat ultrafiltrated plasma. The relative porosity of the grafts allowed for transudation of a protein rich fluid.

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Tanski W, Fillinger M. J Vasc Surg 2007;45(2):243-249.

 

 

 

 

 

 

 

This results in a hygroma formation. I remember seeing this in AV graft fistulae back in the 90’s -after flow was introduced, the grafts would start sweating! The newer grafts are lower porosity and this is seen very infrequently. Drs. Morasch and Makaroun published a paper in 2006 comparing parallel series of patients who received the original Gore Excluder (OGE), the currently available Excluder Low-Permeability Device (ELPD), and the Zenith device (ZEN). Sac enlargement occurred in equal measure between OGE and ZEN but zero was reported for the ELPD.

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Haider S et al. J Vasc Surg 2006;44(4):694-700.

The ELPD had higher rates of sac shrinkage than the OGE, and equal rates of sac shrinkage compared to ZEN.

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Haider S et al. J Vasc Surg 2006;44(4):694-700.

The diagnosis in my patient’s case came about through serial followup through a decade. While I doubt that the aneurysm would have ruptured in the same way as in a Type I, II, or III endoleak, I am sure it would have progressed to developing symptoms from aneurysmal distension or local pelvic compression.

Is it possible to visualize this kind of endoleak at the time it is suspected? I came across a case series from the Netherlands using Gadofosveset trisodium which takes longer to clear than the usual Gd-based MR contrasts and they successfully visualized transudative leaks in 3 serial patients with the original Excluder graft.

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Cornelissen SA et al. J Vasc Surg 2008;47(4):861-864.

The problem is that Gd-based contrasts have toxicity, especially for patients with poor renal function. The protocol is time consuming. And I suspect that ten years out, a lot of grafts will have positive findings, especially cloth based grafts that are sutured to their supporting stents, without clinical basis for treatment as their sacs size are likely stable on a year to year basis.

That said, as we are well into the second decade of commercially available stent grafts, it is even more important than ever to continue lifelong followup even for what is assumed stable, patent grafts and anatomy.

3DVR -Very Helpful in Planning Open Surgical Cases

3DVR CIA Endart

The images above show a patient with on isolated occlusion of his left common iliac artery. He was young, in his forties, but was a heavy smoker and suddenly developed claudication of his left leg which interfered with his work. He quit smoking and did not progress with exercise. Discussion involving possible stenting was made and initially offered but he turned it down because erroneously he assumed that his father’s coronary stents were the same as an iliac stent in terms of longevity. I do think that common iliac and aortoiliac occlusive disease is well treated with stents, but I felt it was possible to do a common iliac endarterectomy. We went over these images together and he settled on proceeding with endarterectomy.

The images show how well the 3D Volume Rendering, which I mentally call Virtual Reality, of CTA makes it possible to plan out operations and exposures virtually. The bottom left image shows the surgeon’s eye view of the exposed vessel.

Below, the virtual and the actual are juxtaposed.

3DVR CIA Endart Exposure

The outline on the virtual image (volume rendered) shows the areas of retraction -for the trainees, the retractor systems work to make quadrilaterals out of linear incisions, and as a rule, the incision should be twice the length of the square that you want to expose. The end points of the endarterectomy were at the aortic and iliac bifurcations.

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The arteriotomy was repaired with a patch at the iliac bifurcation -the common iliac was large and was repaired primarily.

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The specimen below was fibrocalcific. The thing about this disease is that the plaque truly has no endpoint -intimal thickening and mild plaque was present that could be taken all the way to the aortic root and to the feet on the other end!

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This patient did very well and had palpable pulses. He did not develop neointimal hyperplasia and successfully quit smoking.

One of the exciting developments is the ongoing development of wearable virtual reality and display solutions -particularly from the gaming industry. The gaming industry ironically drives all computer imaging because that is where the money is at. The advances in imaging trickle down to medicine -the VR images seen here are the result of the same algorithms that drive first person shooting games. It would be great to see this displayed intraop on a HoloLens, on a virtually positioned screen behind the assistant!