3D printing in vascular surgery

3D printing for preoperative planning

3D printing has a major role in preoperative assessment and simulation of surgical and endovascular procedures. 3D models are constructed to aid clinical doctors and scientists understand the anatomy and disorders of the thoracic and abdominal aorta .

Ho et al. indicated that vessel diameters acquired from pre-3D printing computed tomography (CT) images and images obtained from model's CT scan presented only minor differences within 1 mm error, ensuring the highest anatomical accuracy of the rapid prototype . Furthermore, the 3D printed models used in the preoperative planning over the last 5 years have decreased the procedural time and complication rates with regard to surgical management of abdominal aortic aneurysms (AAA) and aortic dissections. The use of 3D printing has been also described in preoperative planning of portosystemic shunt closure devices .

3D printing has been used for preoperational planning of endovascular treatment for various aortic stenosis pathologies, such as hypoplasia , aortic valve stenosis , pulmonary valve stenosis , and internal carotid artery stenosis , but also for portal vein stenosis . Aortic dissection has been shown to be an aortic pathology that 3D printed models could enable direct visualization and assessment of anatomical features, regarding the size and shape of true and false lumens, something which should lead in the best clinical decision making and medical treatment . Notably, the greatest part of the vascular 3D printing literature refers to the preoperative simulation of AAA. Tangible 3D models allow vascular surgeons to study the unique anatomical structure or abnormalities of the aorta, in order to have a better insight of the best endovascular treatment modality (appropriate endografts, custom-made modification, chimney- or fenestrated endovascular repair) and the assessment of technical and clinical success .

Meess et al. applied 3D printing for preoperative guidance and surgical planning in an AAA treated with fenestrated endovascular aneurysm repair (FEVAR). The patient's specific 3D model served as a diagnostic tool and training “device” in a risk- free environment. Also, the phantom proved to be a useful tool in detecting possible periprocedural complications. Therefore, the model guided the authors to modify their surgical plan in order to avoid any complication, decrease the procedural time, and avoid unnecessary challenges during surgery. Moreover, the team had time to practice with the implanting device, leading to a reduction in radiation exposure of both patient and surgical staff, anesthesia, and contrast agent to the patient. 3D printing model has been shown to be more effective with respect to preoperational planning compared to the standard planning based on CTA diagnostic imaging alone . Takao et al. reported on applied rapid prototyping in order to produce a model of hollow splenic artery aneurysm. The 3D model served as a simulation aid to endovascular treatment. An FDM-type desktop 3D printer and computed-tomography angiography data were used. While the thickness of the layer was 0.2 mm, thinner layers could be further produced using other 3D printing techniques, such as STL and inkjet printing. Nonetheless, the mean cross-sectional areas were slightly smaller than those of the original mask images, with a maximum difference of 0.33 cm ² , rendering a precise and accurate model .

Rapid prototyping can clearly help endograft planning when facing issues such as dealing with complex anatomical issues and CT imaging that hinder proper and thorough reconstructions and measurements. Likewise, Tam et al. reported on a patient who had an infrarenal aortic aneurysm of 6.6 cm with severe neck angulation of approximately 90°. Because of the hostile neck anatomy, the most suitable endograft choice and the proper mode of intraoperative deployment of the device was obscure. Consequently, the CT data were segmented, processed, and converted into a stereolithographic format representing the lumen as a 3D volume, from which a full-sized replica was printed within 24 h. Careful inspection of the 3D aneurysm model revealed an adequate infrarenal sealing zone and led to the optimal choice of an endograft. Accordingly, the authors suggested that the rapid prototype can assist the surgical team not only in AAA cases of angulated neck anatomy, but also in cases of short or conical neck .

Another complex neck anatomy of infrarenal AAA was successfully managed with the use of 3D printed models. In this case, the infrarenal AAA had a severely angled (approximately 90°) and short neck. The greatest difficulty in such cases is to predict the possible changes in neck shape, after the deployment of a stent, since this could lead to deployment outside or improper deployment of the endograft leading to inadvertent coverage of renal ostia or improper sealing. Hence, it is crucial to find a way to predict any potential outcome after the stent deployment. Since this cannot be easily done with the available conservative imaging methods, surgeons can draw useful information by means of creating a 3D printed model. The model helped the team in surgical planning and the selection of the appropriate approach, thus minimizing the intervention time .

3D printing has been also implicated in decision making and treatment of challenging thoracic aortic aneurysms (TAA) and dissections. In such cases, the main problem focuses on prediction of the change of the aortic arch angle after stent deployment, which could possibly result in the formation of a new lesion or even cause reverse extension. Thus, production of 3D models aids in better decision making and facilitates the optimal choice of endograft. In addition, surgical simulation enables vascular surgeons to avoid any difficulties in the use of guidewires and changes their approach in order to ensure the technical success of surgery .

Knox et al. reported on three patients with arterial abnormalities, those being high-grade stenosis of the right common artery bifurcation, basilar tip aneurysm, and abdominal aortic aneurysm. The created 3D models were accurate enough to reproduce flow dynamics of the altered anatomy. Obviously, the unique advantage of 3D printing is that the surgeon can have a preoperative hands-on experience with the pathology he plans to interfere with. As one rotates the reconstructed 3D model in every direction and experiments with it, one develops a haptic intuition concerning the best surgical approach . Hence, as noted by Petzold et al., the 3D model introduces a new kind of interaction called “ touch to comprehend.”

A traverse arch hypoplasia model has also been presented. The model was very accurate with respect to magnetic resonance- and X-ray angiographic images with only a minor deviation of 0.36 ± 0.45 mm. One can easily appreciate this accuracy since catheter interventions, especially in children, rely strongly on the proper sizing of stents and balloons, with quite narrow variations. Hence, 3D models have been shown to be useful in terms of determining the size of the balloon, the stent length, and optimal position. Furthermore, modification and advances allow mimicking expansion of the vessel wall during balloon inflation . More specifically, 3D models are not only used for preoperative simulation, but also during the operation as a guide for the specialists, even more in combination with robotic surgery . The models play a major role in testing catheters and wires in a full-scale anatomically accurate vascular model, as the equipment performance can be evaluated in a controlled environment in the patient's unique anatomy .