Step 1: Surgical Anatomy

Normal Anatomy

♦ Although extrarenal Wilms tumor can occur, the vast majority of Wilms tumors occur in one or the other kidney. No side predilection has been observed.

♦ About 5% to 10% of children with Wilms tumor have disease in both kidneys (synchronous, bilateral Wilms tumor).

Anatomic Variations

♦ Variations in renal anatomy can occur. It is critical to recognize certain ones, such as the occurrence of Wilms tumor in a solitary kidney or horseshoe kidney, because these variations will significantly alter the treatment approach.

♦ Variations in the renal vasculature are fairly common. These include multiple renal arteries or veins and a circumaortic or retroaortic left renal vein. However, these variants rarely impact the conduct of a radical nephrectomy and do not need to be exhaustively sought with preoperative imaging.

♦ Variations in the anatomy of the collecting system can also occur, most commonly duplication of the ureter. As with the variations of renal vasculature, variations of the collecting system should not significantly alter the conduct of surgery.

Step 2: Preoperative Considerations

Imaging

Assessment of the Primary Tumor

♦ Ultrasonography is often used as an initial screening study for an infant or young child with an abdominal mass.

♦ Computed tomography (CT) of the abdomen and pelvis is generally the imaging study of choice for patients suspected of having a renal tumor. CT will confirm the presence of a solid renal mass and will also afford the opportunity to visualize the contralateral kidney to confirm its presence (and function) and to exclude synchronous bilateral disease.

Assessment of Vascular Extension

♦ Intravascular tumor extension into the inferior vena cava occurs in about 6% of Wilms tumor cases (Fig. 33-1). Therefore, this should be specifically investigated in the preoperative evaluation of all children with a renal mass because it might alter the conduct of surgery. This investigation can generally be done most easily and accurately using Doppler ultrasonography. Magnetic resonance imaging can also be used to assess intravascular tumor extension but usually requires sedation in young children and so is not routinely used. However, it may be helpful in defining an extensive tumor thrombus that extends up to the level of the hepatic veins or even into the right atrium. Echocardiography may be useful in rare circumstances to demonstrate (or exclude) intracardiac tumor extension.

Figure 33-1

Assessment of Metastatic Disease

♦ The most common site of metastatic spread of Wilms tumor is the lungs; chest CT is the preferred imaging modality for evaluating this site. However, the presence of a small pulmonary nodule is not always metastatic disease; histologic confirmation is required either before to the start of therapy or after administration of three-drug therapy, if the lesion(s) persists.

♦ Other rare sites of metastases, such as the liver, are usually well evaluated with the initial abdominopelvic CT scan.

Pulmonary Function

♦ Children with Wilms tumor occasionally present with pulmonary insufficiency from extensive metastatic disease in the lungs (Fig. 33-2).

♦ The clinical assessment is generally sufficient to determine whether the patient can tolerate general anesthesia; formal pulmonary function studies are not required.

♦ Patients who appear unable to tolerate general anesthesia should have a percutaneous biopsy, if feasible, and a central venous catheter placed so that three-drug neoadjuvant chemotherapy can be initiated. Because Wilms tumor is generally chemosensitive, the tumor burden in the lungs and the functional pulmonary status should improve fairly promptly.

Figure 33-2

Hypertension

♦ About 25% of children with Wilms tumor will present with hypertension. A preoperative assessment of blood pressure should be performed in all patients, with hypertension being medically controlled before surgery. In many patients, but not all, the hypertension will resolve after radical nephrectomy, although it may take some time.

Predisposition Syndrome

♦ Some patients (2%) will have a Wilms tumor as part of their presentation of a Wilms tumor predisposition syndrome (Table 33-1). Patients with “predisposition syndromes” include those with unilateral Wilms tumor and aniridia, Beckwith-Wiedemann syndrome, hemihypertrophy, Simpson-Golabi-Behmel syndrome, and Denys-Drash syndrome.

♦ These patients are currently being treated with neoadjuvant chemotherapy and unilateral nephron-sparing surgery. Appropriate genetic testing may be done as indicated.

Table 33-1 Wilms Tumor Predisposition Syndromes

NAME	GENETIC ABNORMALITY	ASSOCIATED ANOMALIES
WAGR syndrome	11p13 (WTI) deletion	Aniridia, Genitourinary anomalies, mental Retardation
Denys-Drash syndrome	WTI mutation	Nephropathy, intersex disorders
Beckwith-Wiedemann syndrome	11p15 (WT2) abnormalities	Microsoma, macroglossia, visceromegaly, embryonal tumors, omphalocele, hypoglycemia
Sporadic hemihypertrophy	Unknown	Enlargement of one side of the body or part of the body
Simpson-Golabi-Behmel syndrome	X-linked recessive	General overgrowth in height and weight with characteristic facial features