Wilms tumor (WT) is the most common malignant renal tumor in childhood, and 5%–10% of patients have either synchronous or metachronous bilateral disease.¹ Bilateral WT tends to occur in children at younger ages and more often in girls, and it is an important risk factor for the development of renal failure. In particular, those born with a WT1 mutation foreshadow a poor prognosis for renal function.² Survival has dramatically improved over the past several decades, largely due to the adoption of treatment guidelines and clinical trials from both the National Wilms Tumor Study Group (NWTSG) and the International Society of Pediatric Oncology (SIOP).

Although the clinical goals of these 2 groups are similar, the treatment approach has fundamental differences. In general, the recommendation by NWTSG for unilateral disease is total radical nephrectomy (RN) at diagnosis followed by chemotherapy and possibly radiotherapy (stage dependent). Alternatively, the SIOP recommends early biopsy and neoadjuvant chemotherapy followed by delayed nephrectomy. Irrespective of the approach, surgical resection is a mainstay of treatment. Although nephrotoxicity from chemotherapy, radiation and intrinsic renal disease may contribute to the eventual development of renal failure in some patients, the loss of renal mass from tumor resection appears to also be a significant factor.

Partial nephrectomy (PN), or nephron-sparing surgery (NSS), has been advocated in cases of bilateral WT (for which the only alternative is bilateral RN), in cases of multifocal unilateral disease or with Wilms predisposition syndromes (ie Beckwith-Wiedemann, WAGR [syndrome including Wilms tumor, Aniridia, Genitourinary anomalies, and intellectual disability {formerly referred to as mental Retardation}], Denys-Drash, Perlman etc).^3,4

The SIOP approach of neoadjuvant chemotherapy significantly reduces tumor size, decreases the rate of intraoperative tumor spillage and facilitates tumor removal.However, using strict historical criteria, it is estimated that only 3% of tumors are amenable to a PN after chemotherapy.⁵

Improved outcomes can be tied to our ability to refine treatment modalities based on the clinical appearance of the mass as well as its biological factors. Personalized management based on mass size, location in relation to the collecting system and vasculature, response to chemotherapy, histology, mRNA analysis and chromosomal analysis for loss of heterozygosity at 1p and 16q can potentially be used to determine the feasibility of PN.^6,7

Due to the young age of most patients with Wilms tumors, they are at long-term risk of renal insufficiency and end stage renal disease-related morbidity (ESRD). In addition to elevated serum creatinine levels, hypertension can occur as a result of nephrectomy. In a small study of bilateral WT, patients undergoing PN and contralateral RN (8/12 patients, 66%) were more likely to develop hypertension requiring medical therapy compared to bilateral PN (2/10 patients, 20%).⁸ As expected, there was greater renal parenchymal volume after bilateral PN, though compensatory hypertrophy occurred in patients (<8–9 years) with a solitary kidney after PN.

Working with our colleagues in radiology, we have created 3D models to aid surgical planning of patients with complex tumors. Clinical magnetic resonance imaging (MRI) is optimized for printing, often obtaining images in arterial, venous and delayed phases of contrast enhancement. The images are reviewed and relevant anatomy is identified and defined during a collaborative discussion by the radiologist, urologist and engineer. From this segmentation, a dynamic PDF is created on which the anatomy can be manipulated and viewed from different planes or have certain anatomy added/subtracted to better understand anatomic relationships.⁹ A 3D model is then printed to facilitate presurgical discussion among the team and for intraoperative reference (fig. 1).

Figure 1. Recreated MRI 3D model of kidneys with Wilms tumors and critical vasculature (A) and intraoperative manipulation of PDF form (B) allowing real-time measurement of normal parenchyma and tumor for excision (C).

Figure 2. Renal hilum vasculature dissected to allow precise tumor isolation. Segmental arterial blood supply showing apical artery (A), superior anterior artery (B), inferior anterior artery (C), inferior artery (D), posterior artery (E) and renal vein (F).

During NSS, traditional renal surgical techniques include hilar vascular isolation, partial direct compression of parenchyma (surgeon’s fingers, vascular clamp or umbilical tape Rummel tourniquet) to optimize a bloodless field, and the use of Bovie electrocautery to divide the parenchyma. We favor direct compression adjacent to the affected parenchyma while maintaining blood supply to the rest of the kidney preferable to whole kidney warm or cold ischemia, as well as a 1 cm normal margin (confirmed by frozen section) rather than enucleation. Tumors that are indistinctly palpable or that encroach on the renal hilum are further evaluated using intraoperative ultrasound to delineate the deep extent of the tumor, including 3D model correlation. After tumor resection, the collecting system is repaired with absorbable suture, oxidized cellulose and argon beam coagulation, and direct mattress suture approximation of the renal parenchyma/capsule, with externalized drains and internal ureteral stents to aid drainage. Tumor and normal parenchyma are evaluated histologically and genetically for genome-wide single nucleotide polymorphism (SNP) microarray analysis. Though we naturally find tumors arising in the lower pole of the kidney technically easier to resect with these techniques, we do not consider tumors located medially, posteriorly or in the upper pole as a contraindication to a nephron-sparing approach.

RENAL Nephrometry is a complexity score describing the likelihood of complication after PN. In pediatrics, this score correlates with operative time but not necessarily postoperative complications. The majority of tumors that have high-intermediate complexity (a high RENAL score) may still successfully undergo NSS. Our own experience of 33 pediatric renal tumors for planned PN, independently scored by both pediatric urologists and radiologists, showed high inter-observer reliability for this scoring system. Most tumors were of high-intermediate complexity yet successfully underwent PN.¹⁰ Utilization of validated surgical complexity scoring systems will be essential for preoperative planning and when comparing literature on outcomes of pediatric PN.

Many advances have been made in increasing survival in patients with WT. While RN has remained the gold standard in the management of WT, patients with bilateral WT and syndromic WT have increased the utilization of NSS. Given the benefits of PN in adults with renal masses and the impact on cardiovascular health, a paradigm shift toward increased utilization of NSS for WT is warranted. Improvement in preoperative cross-sectional imaging, including the use of 3D models and interactive dynamic PDFs, provide the surgeon with increased understanding of anatomic relationships and risk prior to entering the operating room. Adoption of neoadjuvant chemotherapy can lead to both tumor shrinkage and expansion of the utilization of PN for more WT while ensuring that we still achieve equivalent oncologic outcomes.