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.

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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.

postop-duplex

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.

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!

Arteriovenous fistula after ankle infection –workup and treatment

The patient presented with complaint of right leg swelling and pain that became unbearable as the day progressed. He had had a prior bout of septic ankle joint which occurred after treatment of infected hardware in the other ankle. He did have an aspiration of his joint but no major surgery. His local specialist performed arteriography, found an arteriovenous fistula, and referred him after concluding that an endovascular repair was not possible.

On examination, he had dilated leg veins and a boggy, tender leg without chronic venous stasis changes. There was an audible bruit over the ankle where the fistula was identified. It would have been near the puncture site of an aspiration needle. CT scan showed the arteriovenous fistula along with chronic changes on the arterial and venous sides due to the increased flows.

This included relative dilatation of the anterior tibial artery and the outflow veins. One of the animal models of iliac aneurysm involves creating an arteriovenous fistula of the femoral artery at the groin of a rat –this was an arduous operation done under a microscope which was the final exam of a microsurgery course during my fellowship, but I digress. Arteries respond to perturbations of flow by dilatation, elongation (engendering tortuosity), and plaque formation. Two areas of naturally occurring elongation are the internal carotid artery and the external iliac artery –in both cases, it is sometimes necessary to straighten and cut out excess artery. A high number of patients with tortuous internal carotid arteries –those with kinks and loops, have aortic aneursms. In the case of the external iliac artery, this has been used in the past as conduit for infections of the common femoral artery.

He had the clinical triad for an arteriovenous fistula that persists and grows –trauma, inflammation, and good venous outflow. The pain was due to venous hypertension but I suspect some regional compartmental steal and pressure may be at play as well, but that’s hard to prove. It makes me think there may be a way to create AV fistulae for dialysis access using these principles.

The 3DVR imaging was very helpful in planning the operation, particularly the incision and exposure.

 

Is there an endovascular option? Probably, but why? What are the costs of coils and glues when a few clips and sutures will do? This patient did very well with ligation and division of the fistula. The real magic is our imaging and image processing capabilities.