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.

The Clot Gun: Popliteal Venous Aneurysms Are Not Varicose Veins

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The basics of this air rocket pictured above is the projectile, attached by tube to a large bladder which when compressed by external force, ejects the projectile upwards. These are the same features of a popliteal venous aneurysm. First, the large chamber predisposes to stasis and thrombus formation. This thrombus will form on the flaccid walls which are areas where stasis occurs. During activity, it likely dislodge but catch at the outflow, obstructing it. Pressure builds up in the calf veins below, and flexing the knee and pressing the venous aneurysm ejects the thrombus towards the heart and lungs. Clot Gun.

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The patient is a young woman who was an active college athlete. She had her first pulmonary embolism occur during practice several years prior to presentation. A duplex noted residual thrombus in her right popliteal vein. Over the next several years, she had two more episodes of pulmonary embolism whenever her anticoagulation was stopped. No thrombophilia was detected on workup. She was referred to the Clinic and Dr. Jerry Bartholomew in the Department of Cardiovascular Medicine noted in her records a mention of a dilated popliteal vein. On examination, she had no historical or physical examination findings to suggest a predisposition to pulmonary embolism. A duplex was ordered.

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The duplex showed a 2.8cm popliteal venous aneurysm of the right leg. No acute DVT was seen but swirling rouleaux could be seen on the B-mode video. A CT venogram was ordered.

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No other defect was detected. Operation was planned. Mapping showed no suitable superficial venous conduit, and venorrhaphy was planned. The patient was kept anticoagulated to the day of operation.

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A curvilinear incision (lazy S) was made across the popliteal fossa and careful dissection revealed the aneurysm. It was soft and the vein was normal below in the calf. Above it, there was a tight fibrous band that was contricting it -a popliteal venous entrapment. I released this band. Using a 24 French Foley catheter inserted through a transverse venotomy on the popliteal vein below, the aneurysm was plicated to approximately 1cm diameter, and the catheter removed and the venotomy repaired.

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The nerves were restored to their original position and the wound closed in layers. She recovered well and returned to followup about a month later. Duplex showed a patent vein and she had no symptoms of dyspnea.

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The plan is to have her come off of her anticoagulation after a visit with Dr.Bartholomew. Reviewing the literature, my confreres at Mayo published their 15 year experience with popliteal venous aneurysms and found that 5 of their 8 patients presented with pulmonary embolism, and that most of their complications occurred with bypass repair while aneurysmorrhaphy fared well (reference). Because of their rarity, about 200 cases in the literature, it may be assumed that many are not found until complications occur or never found because pulmonary embolism, the most common complication, results in death. Also, it would be easy for unknowing physicians to assume that popliteal venous aneurysm falls under the umbrella of varicose vein which this is not. They should be treated when found, and in most cases, such as this, venorrhaphy is preferred.

 

Reference

Johnstone JK et al. Surgical treatment of popliteal venous aneurysms. Ann Vasc Surg 2015;29:1084-1089.