Wilms tumor

Most common pediatric renal tumor

80% of all pediatric renal tumors (75% favorable histology Wilms tumor, 5% anaplastic Wilms tumor)

Can present at any age but most common at 2–5 years

Painless abdominal mass, hematuria, hypertension

May be associated with predisposition syndromes

CT CAP

“Claw sign” of normal kidney around the tumor. The mass typically pushes surrounding structures away rather than invading surrounding organs

Surgical excision, adjuvant chemotherapy and possibly radiation

Exceptions for the youngest patients (<2 years) with stage I disease – surgery alone. Also, preoperative chemotherapy and partial nephrectomy for bilateral tumors

About 20% of cases present with metastatic disease

Local recurrence is rare if tumor completely excised

Recurrence increased for those with nodal involvement or tumor rupture

Prognosis largely impacted by stage and tumor histology

Favorable histology better than Anaplasia

Tumor genetics (LOH at 1p and 16q) can predict outcome as well

Renal cell carcinoma (RCC)

Second most common renal tumor in patients 0–30 yr (4%–5%)

Most common renal tumor in adolescents (>12 yr)

Most commonly Translocation type RCC (TFE+)

Difficult to distinguish from presentation of Wilms tumor

May be associated with predisposition syndrome

CT CAP

Typically smaller than Wilms tumors but can vary and some are quite large

More likely to have calcifications than Wilms tumors

Complete surgical excision including removal all involved nodal disease

Clinical trials for those with metastatic disease

Almost 50% will have advanced stage (stage III–IV) disease

Approximately 1/3 have nodal spread

25% with metastatic disease at presentation

Outcome highly dependent on stage.

>85% survival for those with localized disease (even with nodal spread) if completely excised

Poor survival (<25%) for those with metastatic disease

Congenital mesoplastic nephroma (CMN)

The most common renal tumor in infants younger than 6 months of age

Patients younger than 6 months with a renal mass are presumed to have CMN

Classically present as a palpable mass in newborn period

May be detected prenatally, may be associated with polyhydramnios and preterm birth

Imaging studies (typically US) show this tumor to be confined to the kidney and a full staging work up with CT CAP is indicated

Radical nephrectomy is both diagnostic and therapeutic

LN sampling is advocated to obtain accurate staging information should this actually be WT

Traditionally thought of as benign, but recurrent and/or metastatic cases have been rarely reported

Metastases have been reported to occur to the lung, brain, liver, heart, and bone

Risk factors for recurrence include positive surgical margin, cellular subtype

Prognosis is good, especially if treated in first 6 months of life

There is no established follow up for CMN, but serial abdominal US for the first 2 years is likely prudent

Clear cell sarcoma of the kidney (CCSK)

Classically the bone metastasizing tumor with late recurrences

Peak incidence between 1 and 4 years, 2:1 male predominance

No known familial or predisposition syndromes

Present with a firm palpable mass, with 15%–60% reporting pain due to skeletal metastases

Imaging studies are similar to that of WT

Primary radical nephrectomy and LN sampling

Adjuvant therapy includes XRT and multidrug chemotherapy (vincristine, doxorubicin, cyclophosphamide, and etoposide)

With current treatment regimens, brain metastases are becoming more common than the typical bone metastases originally reported

There is a high relapse rate within the first 3 years after treatment, especially in younger patients and those with advanced disease

5-year EFS is 75%–85% with 5-year OS 85%–90%

These patients need to be followed closely

Rhabdoid tumor of the kidney (RTK)

Rare and aggressive

Occasional occurrences of separate CNS primary tumors

80% of these tumors occur in children younger than 2 years of age with a male predominance (1.5:1)

Median age at diagnosis is 10.6 months

Many patients have a germline mutation that predisposes them to this tumor (incomplete penetrance, possible gonadal mosaicism); consider genetic counseling for families

Hematuria is the typical presenting complaint, but symptoms associated with metastatic disease (to brain, lung, liver) are present in up to 80% of cases

Imaging involves CT CAP

Unique to RTK is the need for CNS imaging (brain MRI) given the high risk of metastatic disease to brain; this is more common in patients younger than 1 year at diagnosis

Early radical nephrectomy with LN dissection is the mainstay of treatment

This tumor is resistant to chemotherapy and XRT

CNS involvement is almost universally fatal

4-year OS is between 20 and 36 months

Lower stage (I/II) patients have a 41.8% OS

Higher stage (III/IV/V) have a 15.9% OS

Age influences OS, with younger patients having worse OS than older patients

Intensive follow up is needed for these tumors

Angiomyolipoma (AML)

Classically seen in patients with tuberous sclerosis

Made of fat, muscle, and blood vessels and thus prone to bleed

Retroperitoneal bleeding

Annual monitoring with US and/or MRI for size stability for the duration of life

Embolization is the treatment of choice should hematuria become an issue

All attempts at nephron preservation should be made due to the future risk of possible resections

Higher risk of RCC

Renal medullary carcinoma

Affects patients with sickle cell trait, thus there is an African American predominance

Very aggressive tumor with almost all cases being fatal

>90% of patients present with advanced disease

Imaging with CT CAP

Treatment revolves around radical nephrectomy

Typically will also receive chemotherapy

Survival between 4 and 16 months from diagnosis

Multilocular cystic nephroma (MCN)/cystic partially differentiated nephroblastoma (CPDN)/cystic Wilms tumor (WT) spectrum

These usually present in patients before 2 years of age

Males more often than females in children but more common in females in adulthood

Usually unilateral, presenting with palpable mass

Mimics include multicystic dysplastic kidney, severely obstructed ureteropelvic junction, cellular variant of CMN, CCSK, and cystic RCC

MCN, CPDN, and cystic WT are indistinguishable on radiologic imaging and require surgical pathologic review

MCN – well circumscribed, cysts and septae

CPDN –poorly differentiated tissue or blastemal cells are found in the septa

Cystic WT – more solid structures between the cysts with stromal/mesenchymal and/or epithelial components

Complete resection is considered curative, usually with radical nephrectomy

If using NSS, frozen section to confirm negative margins is mandatory

MCN is a benign lesion, surveillance is all that is needed

Stage I CPDN is followed with surveillance

Stage II CPDN receives chemotherapy

Cystic WT is treated per recommendations for WT

Renal cysts

Rare in children

Usually incidentally discovered on US

Bosniak classification system that is well described in adults is not generally applied to children

Modifications to this system have been made, that include US findings as well as internal flow

Simple cysts (modified Bosniak I and II) can likely be followed with serial imaging without risk of harboring malignancy

Complex cysts (modified Bosniak III or IV) harbor a risk of intermediate or malignant histology, thus radical nephrectomy is advocated

Anything beyond a simple cyst should have an MRI with and without intravenous contrast to assess the cyst wall and for solid components