♦ 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.

Associated Medical Conditions

Renal Function

♦ Patients with Wilms tumor rarely present with renal insufficiency, so formal preoperative assessment of renal function is usually not required.

♦ Patients with a Wilms tumor predisposition syndrome may have intrinsic renal disease, which might not be of clinical significance until a few years later. However, because of this, the Children’s Oncology Group currently suggests that children with a unilateral tumor and an associated Wilms tumor predisposition syndrome (defined below) be managed on a treatment protocol that includes unilateral nephron-sparing surgery.

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

Step 3: Operative Steps

Positioning

♦ Generally, a supine position with a bump under the appropriate flank is best.

Incision

♦ A transabdominal approach to the affected kidney is currently recommended; a flank or laparoscopic approach is discouraged for performing a radical nephrectomy. A variety of incisions can be used based on the size of the lesion, the presence of intravascular tumor thrombus, and the preference of the operating surgeon. These include an upper abdominal/transverse incision, a subcostal incision, a midline incision, and a thoracoabdominal incision. The incision should be large enough that the integrity of the specimen is not compromised on removal from the abdominal cavity, as tumor rupture and spill have significant consequences.

Tumor/Kidney Removal

♦ A full visual and manual exploration of the peritoneal cavity, including the liver surfaces, should be performed, although this is often difficult to do until after the primary tumor specimen has been removed. The occurrence of preoperative rupture should be documented. Although early ligation and division of the renal vessels have been traditionally recommended, it appears that complete mobilization of the affected kidney and associated tumor first protects against inadvertent ligation of mesenteric vessels or even the aorta or inferior vena cava, and so is now recommended.

♦ Dissection generally begins at the lateral margin after the colon and its mesentery have been mobilized medially to expose the kidney and tumor more completely. The posterior surface of the tumor/kidney is also usually an avascular, safe plane of dissection.

♦ Exposure of the superior extent of right-sided tumors may benefit from mobilization of the right hepatic lobe; exposure of the superior extent of left-sided tumors may benefit from medial mobilization of the pancreas and spleen. Generally, the normal adrenal gland can be separated from the tumor and preserved; however, the ability to remove the tumor mass without rupture should not be compromised in an attempt to preserve the adrenal gland.

♦ The inferior tumor dissection should include removal of the ureter in continuity with the kidney. The ureter should be followed from the renal hilum to as low as conveniently possible, where it should be ligated and divided after palpating for the possible presence of intraureteral tumor (Fig. 33-3).

♦ Once the kidney and tumor have been mobilized laterally, posteriorly, superiorly, and inferiorly, the only remaining attachments are medial; these attachments contain the renal artery(s) and vein(s), which should be individually identified and palpated for the presence of tumor thrombus (even with negative preoperative imaging) before ligating and dividing them (Fig. 33-4). Once this is completed, the kidney and tumor should be free and can be passed off the field.

Figure 33-3

Figure 33-4

Lymph Node Sampling

♦ Assessment of locoregional lymph nodes is a critical component of determining the local stage of Wilms tumor and can significantly affect therapy (even in patients with metastatic disease) and so is an essential part of the operation.

♦ Lymph nodes in the pericaval (right-sided tumors) and periaortic region (left-sided tumors) should be removed and submitted for histologic evaluation (Fig. 33-5); visual assessment alone of the lymph nodes poorly predicts their pathologic involvement.

Figure 33-5

Central Venous Catheter Placement

♦ Nearly all children with Wilms tumor will receive adjuvant chemotherapy; thus a central venous access device is generally placed at the time of nephrectomy. One current exception is that patients less than 2 years of age with small (<550 g), favorable histology, stage I Wilms tumor will not be treated with adjuvant chemotherapy (and so will not require central venous access).

♦ Because therapy for favorable histology Wilms tumor, stage I or II, is of relatively short duration (24 weeks) and administered infrequently (once per week), a central venous line is not essential, although it is generally used.

Special Circumstances

Tumor Thrombus

♦ Intravascular extension into the renal vein and atrium presents special surgical challenges. Intravascular tumor extension can occur in Wilms tumor cases; renal vein involvement has been noted in 11% of cases (most often detected at operation) and caval and atria involvement in about 6% of Wilms tumor cases. It should be sought by preoperative imaging and its presence or absence confirmed intraoperatively.

♦ Tumor extension into the renal vein and proximal inferior vena cava (IVC) in most cases can be removed en bloc with the kidney (Fig. 33-6). Thrombus that extends into the vena cava can often be withdrawn from the IVC by opening the IVC (after gaining proximal and distal control). If the thrombus is not adherent to the wall of the IVC and is removed intact, the tumor may still be designated as stage II if none of the other criteria for assessing a higher stage are met.

♦ Proximal and distal control of the IVC can generally be achieved if the superior extent of the thrombus is below the level of the hepatic veins. However, primary resection of tumors with extension into the IVC above the level of the hepatic vein or into the atrium is associated with higher operative morbidity. Thrombus that extends above the hepatic veins may require cardiopulmonary bypass to remove the full extent of disease safely (Fig. 33-7).

♦ Alternatively, neoadjuvant chemotherapy may be given in an attempt to shrink the thrombus to a level below the hepatic veins. This may result in tumor adherence to the wall of the IVC, thereby precluding its complete removal. In this circumstance, ionizing radiation to the IVC and residual tumor thrombus may be indicated.

Figure 33-6

(Courtesy S.J. Shochat.)

Figure 33-7

Bilateral Wilms Tumor/Solitary Kidney

♦ A biopsy is not required in a child with bilateral, solid renal masses because bilateral Wilms tumor is the certain diagnosis (although the histologic subtype will not be known). Neoadjuvant therapy consisting of vincristine, actinomycin-D, and doxorubicin should be initiated.

♦ Bilateral nephron-sparing surgery should be considered in all patients with bilateral Wilms tumor, even if preoperative imaging suggests that the lesions are unresectable. This approach, when combined with adjuvant therapy, provides the opportunity to preserve renal function while maintaining a high probability of cure. Often large lesions compress adjacent normal kidney parenchyma such that at the time of exploration more uninvolved renal parenchyma exists than might have been anticipated by the preoperative imaging (Fig. 33-8).

♦ Operative intervention for local control should be done early, by 12 weeks after initiation of chemotherapy, because little significant further change in tumor size is likely and it is important to determine the exact tumor histology (favorable vs. anaplastic).

♦ When possible, a small rim of normal kidney (0.5–1cm) is included around the resected lesion. At times, however, resection proceeds in the generally well-defined plane between the tumor and kidney (Fig. 33-9). Despite this approach, tumor rarely extends to the surgical margins because there is often a fibrous rim or capsule that surrounds Wilms tumors. In cases where there are numerous small lesions in the kidneys that appear by imaging to be nephrogenic rests or cysts, representative biopsies can be obtained.

♦ It is important to determine whether the collecting system has been entered, which occurs commonly. When such a breach is identified, the cut edges of the violated calyx are closed with chromic suture, often after placing a “double-J” ureteral stent. The decision to place a ureteral stent is based on the degree of disruption of the collecting system and the complexity of its closure. A flank Penrose drain is commonly placed. The Penrose drains are generally removed before patient discharge; internal stents are removed cystoscopically 4 to 6 months later.

♦ If the tumor histology is anaplastic, consideration of performing a completion nephrectomy should be entertained, especially if the surgical margins were positive.

Figure 33-8

Figure 33-9

Step 4: Postoperative Care

Fluid Management

♦ Fluid management is generally routine in the postoperative period, with only moderate third-spacing expected (especially if the bowels are kept within the peritoneal cavity during tumor mobilization and removal). The remaining kidney quickly adapts to providing clearance of extra fluids, and postoperative edema should be minimal.

Pain Control

♦ Effective pain control can often be achieved through an epidural catheter, with or without supplemental intravenous narcotics.

Ileus

♦ A nasogastric tube is used routinely in anticipation of postoperative ileus, which generally lasts from 2 to 4 days.

Histology and Stage

♦ Because biopsies are rarely done before definitive local control, and because staging of Wilms tumor is based on histologic evaluation of surgical specimens (Table 33-2), tumor histology and stage are generally not known until late in the postoperative period. At that time, accurate diagnosis, stage and therapeutic plan will become available and informed discussion can be initiated with the patient’s parents.

Table 33-2 Wilms Tumor Staging

Stage I

Tumor limited to kidney, completely resected. The renal capsule is intact. The tumor was not ruptured or biopsied before removal. The vessels of the renal sinus are not involved.

Stage II

The tumor is completely resected, and there is no evidence of tumor at or beyond the margins of resection, although the tumor extends beyond kidney, as evidenced by any one of the following criteria:

Regional extension of the tumor (i.e., penetration of the renal capsule or extensive invasion of the soft tissue of the renal sinus)

Blood vessels within the nephrectomy specimen outside the renal parenchyma, including those of the renal sinus, contain tumor

State III

Residual nonhematogenous tumor present following surgery and confined to the abdomen. Any one of the following may occur:

Lymph nodes within the abdomen or pelvis involved by tumor

Gross or microscopic tumor remains postoperatively (e.g., tumor cells are found at the margin of surgical resection on microscopic examination)

Tumor spillage occurring either before or during surgery

Tumor treated with preoperative chemotherapy, with or without a biopsy regardless of type (Tru-cut, open, or fine needle aspiration), before removal

Tumor removed in more than one piece

Stage IV Hematogenous metastases (lung, liver, bone, brain, etc.) or lymph node metastases outside the abdominopelvic region are present. Stage V Bilateral renal involvement by tumor is present at diagnosis.