|ECR 2019 / C-1597|
|Image of atypical Wilms tumor|
Wilms tumor, or nephroblastoma, is the most common renal solid mass and abdominal malignancy of childhood and occurs in approximately 1: 10,000 persons. Its peak incidence is at 3-4 years of age, and 80% of patients present before 5 years of age. Is uncommon in neonates, less than 0.16% of the cases.
Wilms tumor is most frequently sporadically, up to 90% of cases. On other occasions, it occurs in hereditary forms associated with other congenital anomalies such as cryptorchidism, hemihypertrophy, hypospadias, and sporadic aniridia. The genetic syndromes that present Wilms tumor are the syndrome WARG, Drash syndrome, and Beckwith-Wiedemann. Chromosome 11 is involved in these less frequent forms. Family Wilms tumor is rare, 1%, and is not associated with mutations on chromosome 11.
The common histology of the tumor is a triphasic appearance consisting of stromal, epithelial and blastemal elements that recapitulate the normal development of the kidney. But, in some cases, they may have a monophasic or biphasic appearance. Less frequently, unfavorable histologies are found such as teratoid and anaplastic forms. The teratoid form has different tissue lines to the kidneys, such as muscle, bone or cartilage. In 10% of the cases, Wilms tumor shows anaplastic histology. Anaplastic and teratoid histology is considered unfavorable with a poor prognosis.
The typical presentation of the Wilms Tumor is asymptomatic abdominal mass. In other cases, it can be presented as anemia, hypertension, fever or hematuria.
The presentation form in the debut of most Wilms tumor are solitary lesions, but at least 12% of patients can develop a multifocal tumor in the same kidney. Approximately 6% of patients present synchronous bilateral renal tumor.
Screening for suspected abdominal tumor is performed with US, but US is operator-dependent with a limited field of view in addition to other technical limitations. The evaluation with magnetic resonance (MR) imaging or computed tomography (CT) is generally necessary for optimal staging and operative planning.
The appearance of Wilms tumor at US is variable. Usually, the tumor is heterogeneous with hypoechoic and anechoic areas representing hemorrhage, necrosis, and cysts. Calcifications are seen in 9% of patients. US with color Doppler imaging is a sensitive modality for the tumor spread into the inferior vena cava (IVC).
At CT, the tumor usually appears as a large, heterogeneous, intrarenal mass that enhances the normal renal parenchyma adjacent. Hypoattenuating foci of necrosis and old hemorrhage are common, and fat attenuation may also be seen. Calcifications are seen in approximately 15% of cases.
At MR imaging, the tumor is typically heterogeneous, lobulated, and hypointense compared with the kidney on T1-weighted images and hyperintense on T2-weighted images. Foci of increased signal intensity on T1-weighted images representing hemorrhage may be observed. After administration of gadolinium, the tumor enhances less avidly than the adjacent kidney.
Preoperative diagnosis and radiological follow-up are crucial for the success of the therapy. Surgical resection is mandatory for staging and treatment. Staging of Wilms tumor is eminently surgical. The National Wilms Tumor Studies (NWTS) classifies the tumor in V stages.
Although Wilms tumor is a malignant tumor, the prognosis is excellent with multiple therapy (surgery, chemotherapy and radiotherapy). The 5-year survival rate of 90%, reaching 95% in tumors <4 cm, and 70% for metastatic disease.
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