Wilms Tumor

The Wilms tumor, also known as a nephroblastoma, is a renal malignancy typically occurring in children that is thought to have been first described in 1814 by Thomas. F Rance (Figure 47.1).
It was also subsequently described by Joseph Eberth’s 1872 manuscript on a young child who presented with bilateral renal tumors.
However, it is named after Dr Max Wilms, a German surgeon who formally described the tumor and its histology in 1899 through the addition of several cases of children’s kidney tumors to the literature.¹
Before the 1920s, very few surgeons attempted to remove these tumors from the bodies of their young patients and those who did experienced mortality rates as high as 25%.²
Two-year survival rates of children with this tumor have evolved from less than 10% in 1915 to 90% in 1985. There has been continuous improvement in survival rates owing to advances in management such as radiotherapy and modulated chemotherapy.³
M. Wittenborg, a radiation oncologist, developed one of the innovative treatment techniques that are still used to supplement surgical resection.

RELEVANT ANATOMY

Wilms tumor arises from primitive embryonic renal tissue and is typically an intrarenal solid tumor located in the retroperitoneum.
The retroperitoneum, defined as the space between the posterior parietal peritoneum and the transversalis fascia, can be divided into 3 zones:
- The central zone: aorta, inferior vena cava, pancreas, and duodenum
- Two lateral zones: the kidneys, ureters, and ascending/descending colon
- Pelvic zone: rectosigmoid, iliac vessels, and urogenital organs⁴
Wilms tumors adhere to adjacent structures including but not limited to the diaphragm, liver, and the spleen.
Careful attention to vessels including the aorta, renal vein, inferior vena cava, and superior mesenteric vessels is crucial to prevent iatrogenic injury.

Figure 47.1 Wilms tumor. Typical gross appearance of Wilms tumor with large, bulging variegated mass showing areas of necrosis and hemorrhage. (Reprinted with permission from Jennette JC, Heptinstall RH, eds. Heptinstall’s Pathology of the Kidney. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2007.)

EPIDEMIOLOGY AND ETIOLOGY

Wilms tumor is the most common primary renal malignancy of childhood.
It accounts for 95% of renal tumors in children <15 years of age and 6% of all pediatric malignancies.⁵

Incidence: The annual incidence of renal tumors is about 8.1 cases per million children, resulting in 600 to 700 new cases each year in North America.⁶

Two-thirds of cases are diagnosed before the age of 5 years, 95% are diagnosed before the age of 10, and the mean age of diagnosis is 3 years of age.
African-American children are at a greater risk of developing Wilms tumor, while Asian children have reduced risk.⁷
Wilms tumor is associated with loss of function mutations of a number of tumor suppressors and transcription genes, including mutations of WT1, p53, FWT1, and FWT2 genes.

Etiology: There are a number of theories surrounding the etiology of Wilms tumors, but the exact etiology is still unknown.

CLINICAL PRESENTATION

Classic presentation: Children with Wilms tumor commonly present with a palpable abdominal mass. Other common symptoms include swelling, hematuria, fever, and hypertension.⁸

A small subset of patients can present with subcapsular hemorrhage and can present with rapid abdominal enlargement, anemia, hypertension, and sometimes fever.
The most common site of metastasis is the lung; however, children rarely present with respiratory symptoms.
Other common renal tumors of childhood include clear cell sarcoma, rhabdoid tumors, renal cell carcinoma, and mesoblastic nephroma.
These collectively account for about 5% of renal tumors in childhood.
The classic physical examination finding is a firm, nontender, smooth mass that is eccentrically located and rarely crosses the midline.
Between 5% and 10% of cases present with bilateral Wilms tumor, and this presentation is common in patients with a genetic predisposition to Wilms tumor, such as Beckwith-Wiedemann syndrome (Figure 47.2), WAGR syndrome, or Denys-Drash syndrome.
- Additional associations include hemihypertrophy, Klippel-Trenaunay-Weber, Perlman syndrome, and genitourinary malformations such as horseshoe kidney.

Figure 47.2 An 11-month-old girl with Beckwith-Wiedemann syndrome, bilateral nephroblastomatosis, and presumed bilateral Wilms tumor. Coronal contrast-enhanced CT image shows multiple bilateral low-attenuation renal masses (asterisks) due to nephrogenic rests and multifocal Wilms tumor. (Reprinted with permission from Lee EY. Pediatric Radiology: Practical Imaging Evaluation of Infants and Children. Philadelphia, PA: Wolters Kluwer; 2018.)

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