For decades, open radical nephrectomy (ORN) was the gold standard for treatment for all renal masses; however, with the advent of minimally invasive approaches, the indications for ORN are diminishing.¹ Nephron-sparing robotic assisted laparoscopic partial nephrectomy and open partial nephrectomy are two minimally invasive techniques which may be selected to treat localized small renal tumors.² Anatomic relationship of the tumor with other structures and its location within the kidney are some factors that influence the surgical planning and decision for minimally invasive partial nephrectomy.³ The decision to perform a partial nephrectomy and which approach to take is a complex interaction between various patient factors (i.e. comorbid conditions, age, and body habitus) and renal tumor morphology.⁴

Pre-operative three-dimensional (3D) printed models of renal mass are valuable tools that may facilitate surgical planning by allowing surgeons to assess tumor complexity as well as the relationship of the tumor to major anatomic structures such as the renal vasculature and collecting system.⁵ Computed tomography (CT) images are generally used to create 3D printed models;^6,7 however, magnetic resonance imaging (MRI) is an attractive alternative, since it offers superior soft-tissue characterization and flexible image contrast mechanisms, and avoids the use of ionizing radiation or iodinated contrast. The objective of this study was to determine how patient-specific 3D printed renal tumor models derived from MRI data can influence pre-surgical planning.

Ten renal malignancy cases were retrospectively selected based on perceived complexity of the surgery. Nephrometry scores ranged from 6a-10p. A 3D post-contrast fat-suppressed gradient-echo T1 weighted sequence with a spatial resolution of 1.4 mm x 1.4 mm x 2mm was used to generate the 3D printed models. Image segmentation and 3D visualization was performed (Figure 1); and 3D objects were manually edited and converted to .STL format for printing (3-matic, Materialise, Leuven, Belgium). High-fidelity, patient-specific 3D renal tumor models were 3D printed in multiple colors (Connex 500, Stratasys, Eden Prairie MN (Figure 2)). Renal malignancy cases were reviewed by three attending urologists and six 4th year urology residents in a blinded fashion with imaging alone and with imaging in addition to the 3D model. A questionnaire was completed after both scenarios to assess surgical approach and planning with and without the patient-specific 3D model (Table 1). The presumed pre-operative approaches with and without the model were compared. Any change between the presumed approach and actual surgical intervention was recorded. The model resulted in a change in surgical approach in all cases (Table 2). Two of the three attending urologists changed their surgical plan in five cases (50%) and the 3rd attending urologist changed the surgical plan in three cases (30%). Decisions about clamping and collecting system repair changed the most with the 3D model. The residents tended to alter their approach a greater percentage of the time as compared to the attending urologists, with three residents changing their surgical plan in six cases (60%), one in five cases, one in four cases, and one in a single case. All physicians reported that the models helped with regards to surgical approach for partial nephrectomy. 88% of participants believed that the 3D printed model helped significantly with comprehension of anatomy, 63% reported that the 3D printed model increased their confidence that they correctly planned the procedure, and 75% said that they would use the 3D printed models often if they were available. As our results suggest, it is possible to create 3D printed renal tumor models from MRI data; and these preoperative 3D printed renal tumor models data may facilitate surgical planning. Specifically, pre-operative 3D printed renal mass models could promote nephron-sparing surgery and preservation of healthy parenchyma, as surgeons gain a better understanding of the size and location of a tumor in relation to normal tissue and vital structures such as the arteries, veins, and collecting system. We have demonstrated the feasibility of creating high-fidelity 3D printed models from MRI data in the context of renal malignancies. These 3D printed models may alter the surgical plan, especially for trainees and young surgeons. Future, outcome based studies may help to determine the impact of these 3D printed models on surgical outcomes and patient care.