–Rhabdoid nephroblastoma (2%): acidophilic cytoplasm, metastatic spread also to fossa posterior of brain

–Mesoblastic nephroma: congenital form, mean age at diagnosis, 2 months; occasionally translocation t (12;15) (p13;q25); similar to infantile fibrosarcoma

11.5Clinical Manifestations

•Visible and palpable, clinically often asymptomatic abdominal mass

•Palpation must be done with care to reduce the risk of tumor rupture

•Unclear febrile episodes, anorexia, vomiting

•Micro–or macrohematuria in 20–25% of patients

•Hypertension in children with renin-producing tumor cells

•Rarely associated with secondary polycythemia, which is due to expression of erythropoietin by tumor cells

•Occasionally, varicocele, inguinal hernia, acute renal failure, coughing, pleural pain, and/or pleural effusion in children with pulmonary metastases

•Special symptoms in association with congenital anomalies (see above)

–Coagulopathy caused by acquired von Willebrand syndrome

–Extension of tumor/thrombus to vena cava inferior (in about 8% of children), which may be the cause of cardiac insufficiency and pulmonary emboli

–Metastatic disease in 13% (lung, liver, lymph node, bone, brain)

11.6Laboratory Diagnosis

•Exclusion of renal failure, high level of serum calcium in children with rhabdoid nephroblastoma

•Urine: microhematuria; after concentrating urine, malignant cells may be detected

•Acquired von Willebrand coagulopathy in about 8% of patients

•Differential diagnosis of neuroblastoma: 24 h urine catecholamine analysis

11.7Radiological Diagnosis

•Conventional abdominal radiography: intestinal displacement by tumor mass with punctuated calcifications (in 2–3%)

•Ultrasound, computed tomography (CT) and/or magnetic resonance imaging (MRI; with contrast urography) of the abdomen, including the hepatic area (metastases) and chest CT