Wilms Tumor (Nephroblastoma)
This is a malignant neoplasm that is bilateral in 10% of cases. As a rule, it is asymptomatic, but is accompanied by microhematuria in a quarter of cases. Pain or arterial hypertension is atypical.
About 15% of cases are associated with congenital anomalies (cryptorchidism, horseshoe kidney) or genetic syndromes:
- Beckwith-Wiedemann (Beckwith-Wiedemann): accompanied by macroglossia and gigantism.
- Denys-Drash (Denys-Drash): pseudohermaphroditism (median age of tumor detection is 18 months).
- Sotos, Bloom (with immunodeficiency), Perlman syndromes, and aniridia.
Morphologically, it is a solid mass with a fibrous pseudocapsule. The tumor tends to invade the renal vein and inferior vena cava, forming a tumor thrombus that can reach the right atrium. It metastasizes predominantly to para-aortic lymph nodes, as well as hematogenously to the lungs and liver.
Diagnostic Imaging of Nephroblastoma
The diagnostic algorithm begins with an ultrasound examination.
- Ultrasound: The tumor appears as a large heterogeneous mass, where the cystic component often predominates over the solid hyperechoic one. Normal renal parenchyma is stretched along the periphery of the node, forming the so-called claw sign (claw sign). Ultrasound is excellent for detecting venous thrombosis and assessing the mobility of the mass.
- Gadolinium-enhanced MRI: Considered the "gold standard". The tumor is hypointense on T1-weighted images and variable on T2-weighted images, taking up contrast less avidly than healthy parenchyma. MRI is critical to rule out nephroblastomatosis or a second tumor in the contralateral kidney.
- Chest CT: Mandatory to screen for pulmonary metastases, although its prognostic value for very small foci remains controversial.
Early Childhood Tumors (Under 1 Year)
In newborns and infants, the spectrum of neoplasms has distinct features:
- Mesoblastic Nephroma (Mesoblastic Nephroma). Almost always detected in the first 3 months. On ultrasound, it appears as a homogeneous solid mass with a hypoechoic periphery. The main difference from nephroblastoma is that mesoblastic nephroma actively takes up the 99mTc-DMSA isotope and rarely metastasizes. The prognosis is excellent.
- Rhabdoid Tumor (Rhabdoid Tumour). Occurs in the first year of life. This is the most aggressive tumor (up to 2% of all pediatric renal neoplasms). It is characterized by early metastasis to the brain and liver. On imaging, it is indistinguishable from Wilms tumor, but may be accompanied by nonspecific hypercalcemia and synchronous primitive neuroectodermal tumors of the posterior cranial fossa.
Other Malignant Neoplasms
In addition to classical Wilms tumor, less typical forms occur:
- Clear Cell Sarcoma. Histologically classified as an unfavorable type. Its distinguishing feature is that it predominantly metastasizes to bones; therefore, bone scintigraphy with 99mTc-MDP is mandatory for staging.
- Renal Cell Carcinoma (Renal Cell Carcinoma). Rare in children (less than 1%), with a mean age of onset around 9 years. It more commonly presents with flank pain. Histologically, these are high-grade tumors (high-grade) and may contain ring-like calcifications. A third of cases are associated with tuberous sclerosis or neuroblastoma.
- Secondary Involvement (Lymphoma and Leukemia). Observed in 12% of children with non-Hodgkin lymphoma (especially Burkitt lymphoma). Ultrasound reveals enlarged kidneys with altered echostructure due to multiple nodules or diffuse infiltration.
Briefly: answers to topical questions
What are the causes and manifestations of urate nephropathy during leukemia chemotherapy?
The cause of urate nephropathy during leukemia chemotherapy can be tumor lysis syndrome, characterized by rapid cytolysis and massive breakdown of blast cells, leading to hyperuricemia and acute renal failure. Administration of a large volume of fluids before and during initial chemotherapy, combined with the excretion of tumor metabolites, can lead to renal obstruction or urate nephropathy.
Manifestations of the disease:
- Acute form — tubular obstruction by urate crystals with the risk of developing acute renal failure, which is sometimes irreversible.
- Chronic form — urate interstitial nephritis with the gradual development of chronic renal failure.
- Urolithiasis — urate nephrolithiasis.
To remember the specifics of clear cell sarcoma, use its alternative name — BMRT (Bone Metastasizing Renal Tumor). If a child with suspected Wilms tumor has bone lesions but no lung lesions, suspect clear cell sarcoma.
Class and exam questions
Can ultrasound or CT differentiate benign multilocular cystic nephroma from cystic Wilms tumor?
No, imaging methods cannot reliably differentiate between benign and malignant multilocular cystic variants. Therefore, nephrectomy or resection is always recommended.
What renal complication can occur at the initiation of leukemia chemotherapy?
Massive fluid overload and excretion of tumor metabolites can provoke the development of urate nephropathy and acute renal obstruction.
Why is contrast-enhanced MRI necessary for Wilms tumor?
Gadolinium administration is essential for accurately determining tumor borders, guiding biopsies, and, most importantly, evaluating the contralateral kidney for occult nephroblastomatosis or a second tumor.
What else to study on this topic
- Staging of Wilms Tumor According to the NWTSG System (USA) and Differences in the SIOP Approach
- Specifics of Diffuse Nephroblastomatosis and Management Tactics
- Tumor Thrombi in Renal Neoplasms: Evaluation of the Inferior Vena Cava
- Multilocular Cystic Nephroma: Bimodal Distribution and Diagnosis
- Paratesticular Rhabdomyosarcoma and Other Scrotal Masses in Children
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