A Minimally Invasive Alternative for the Treatment of Nutcracker Syndrome Using Individualized Three-Dimensional Printed Extravascular Titanium Stents
Nutcracker syndrome (NCS), also known as left renal vein (LRV) hypertension, is a rare condition caused by the compression of the LRV between the superior mesenteric artery (SMA) and the aorta. This compression leads to a variety of clinical manifestations, including hematuria, proteinuria, left flank pain, pelvic congestion syndrome in females, and left varicocele in males. While conservative management is often recommended for mild cases, surgical intervention becomes necessary for patients with severe symptoms or when conservative treatments fail. Traditional surgical approaches, such as open vascular surgery and endovascular stenting, have been employed but are associated with significant risks and complications. This study explores a novel, minimally invasive approach using individualized three-dimensional printed (3DP) extravascular titanium stents (EVTSs) for the treatment of NCS, demonstrating its safety and efficacy.
Background and Rationale
NCS is a challenging condition to manage due to its varied clinical presentation and the complexity of its underlying anatomical pathology. The compression of the LRV between the SMA and the aorta leads to increased venous pressure, resulting in symptoms such as hematuria, proteinuria, and pelvic congestion. Conservative management is often the first line of treatment, but surgical intervention is required for patients with persistent or severe symptoms. Traditional surgical options include open vascular surgery, laparoscopic techniques, and endovascular stenting. However, these methods are not without risks, including stent migration, thrombosis, and the need for long-term anticoagulation therapy.
The advent of 3D printing technology has opened new avenues for personalized medical treatments. By creating patient-specific implants, 3D printing allows for precise anatomical fitting, potentially reducing complications and improving outcomes. This study aimed to evaluate the clinical and radiographic outcomes of patients with NCS treated with individualized 3DP EVTSs, hypothesizing that this approach would provide a minimally invasive, effective, and safe alternative to traditional surgical methods.
Methods
The study was conducted at Tangdu Hospital, The Fourth Military Medical University, Xi’an, Shaanxi, China, and included 17 patients diagnosed with NCS. The inclusion criteria were based on clinical symptoms, LRV diameter ratio, and the angle between the SMA and the aorta. Patients with primary or secondary kidney disease, hypertension, or previous surgical management were excluded.
Pre-operative planning involved the use of 64-detector computed tomography (CT) scans to obtain detailed anatomical images of the LRV, SMA, and aorta. These images were processed using Mimics and 3D-DOCTOR software to create 3D models of the kidneys. The models were then printed using a fused deposition modeling (FDM) 3D printer to facilitate surgical planning.
The EVTSs were designed using Siemens NX software, based on the individual patient’s LRV anatomy. The stents were designed with raised edges and a porous mesh to improve tissue adherence and prevent migration. The stents were printed using medical-grade titanium alloy powder with a precision setting of 200 mm. Each stent was customized to fit the patient’s anatomy, with lengths ranging from 16.1 to 19.3 mm and weights between 3.1 and 4.3 g. The stents were sterilized using ultrasonic cleaning and ethylene oxide sterilization before implantation.
The surgical procedure was performed laparoscopically under general anesthesia. The patient was placed in the right lateral position, and a pneumoperitoneum was established. The LRV was exposed by dissecting the peritoneum and Gerota fascia. The fibrous tissue around the LRV between the SMA and the aorta was released and resected to create space for the stent. The EVTS was then placed around the LRV and secured between the SMA and the aorta. The SMA was sutured to the stent to prevent migration. The procedure was completed with the removal of the urethral catheter and abdominal drainage tubes within a few days post-surgery.
Results
The study included 17 patients (15 males and 2 females) with a mean age of 20.2 years. The mean duration of surgery was 75 minutes, with a mean blood loss of 20 mL. Pre-operative and post-operative CT and Doppler ultrasound (DUS) examinations revealed significant improvements in the angle between the SMA and the aorta, LRV diameter, and peak blood flow velocity. The angle between the SMA and the aorta increased from 18.7° to 48.0°, the LRV diameter decreased from 10.6 mm to 8.4 mm, and the peak blood flow velocity increased from 12.4 cm/s to 18.5 cm/s. In patients with left varicocele, the mean diameter of the left spermatic vein decreased from 3.7 mm to 1.3 mm.
All patients experienced relief of symptoms within 5 days post-surgery, with no complications observed during the follow-up period of 24 to 42 months. The stents remained stable, with no cases of migration or restenosis. The results demonstrated that the 3DP EVTSs effectively relieved the compression of the LRV, leading to improved clinical and radiographic outcomes.
Discussion
The findings of this study suggest that individualized 3DP EVTSs offer a safe and effective minimally invasive alternative for the treatment of NCS. The use of 3D printing technology allowed for the creation of patient-specific stents that precisely fit the anatomical structure of the LRV, reducing the risk of complications such as migration and thrombosis. The laparoscopic approach minimized surgical trauma, resulting in shorter recovery times and reduced post-operative morbidity.
The design of the EVTSs, with raised edges and a porous mesh, ensured stability and improved tissue adherence. The use of titanium alloy provided the necessary compressive strength to withstand the forces exerted by the SMA and the aorta, preventing stent collapse. The surgical technique, which involved the careful dissection of the fibrous tissue around the LRV and the secure fixation of the stent, further contributed to the success of the procedure.
Compared to traditional surgical methods, the 3DP EVTS approach offers several advantages. Open vascular surgery and endovascular stenting are associated with significant risks, including stent migration, thrombosis, and the need for long-term anticoagulation therapy. The laparoscopic placement of 3DP EVTSs minimizes these risks, providing a safer and more effective treatment option for patients with NCS.
Limitations
While the results of this study are promising, there are several limitations that warrant discussion. First, the study did not include a control group treated with traditional surgical methods, making it difficult to directly compare the outcomes of the 3DP EVTS approach with those of other treatments. Second, the sample size of 17 patients is relatively small, and larger studies are needed to confirm the findings. Third, the follow-up period of 24 to 42 months, while substantial, may not be sufficient to assess the long-term efficacy and safety of the 3DP EVTSs. Further studies with longer follow-up periods are recommended to evaluate the durability of the stents and the potential for late complications.
Conclusion
The use of individualized 3DP EVTSs for the treatment of NCS represents a significant advancement in the management of this challenging condition. The study demonstrated that this minimally invasive approach effectively relieves the compression of the LRV, leading to improved clinical and radiographic outcomes. The patient-specific design of the stents, combined with the precision of 3D printing technology, reduces the risk of complications and enhances the safety and efficacy of the procedure. While further research is needed to confirm these findings, the 3DP EVTS approach offers a promising alternative to traditional surgical methods for the treatment of NCS.
doi.org/10.1097/CM9.0000000000000255
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