A palpable abdominal mass detected during a routine office visit is often the first indication of the presence of this rare but highly treatable tumor of childhood. A child cured of Wilms tumor requires on-going follow-up for potential long-term complications.
The best known of the several syndromes associated with an increased risk of Wilms tumor is Beckwith-Wiedemann syndrome, characterized by exomphalos, macroglossia, and gigantism. Isolated hemihypertrophy is also associated with an increased risk of Wilms tumor. Several genes have been identified in association with subgroups of Wilms tumor patients; the most widely studied are the Wilms tumor-1 (WT-1) and WT-2 genes, both located on chromosome 11. WT-1 gene is a tumor-suppressor gene and transcriptional activator important in fetal development.2 Wilms tumor is associated with mutations, deletions, and aberrant expression of the WT-1 gene.
The majority of Wilms tumors have a characteristic triphasic histology (see Figure 1). This favorable histology variant consists of a blastemal component of clumps or sheets of small blue cells, an epithelial component in which the cells form pseudotubules, and a stromal component. Five percent of patients have an "unfavorable histology" characterized by focal or diffuse anaplasia. Other renal tumors including clear cell sarcoma and rhabdoid tumors of the kidney were historically considered unfavorable histology variants of Wilms tumor, but are today recognized as distinct renal tumors of childhood. Histology is a major prognostic factor in Wilms tumor patients and, as such, is an important criterion in delineating adjuvant therapy.
Under your care: Presentation
Imaging and referral for evaluation
Ultrasonography (US) is usually the initial imaging modality in a child with an abdominal mass. US can distinguish a solid mass from hydronephrosis or other pathologic condition, and is an excellent modality for assessing the patency of the renal vein and vena cava in a child.
A solid mass demonstrated by US is usually studied further with computed tomography (CT), which can more clearly delineate the anatomy of the primary tumor and assess the remainder of the abdomen for metastatic disease, most often in the regional lymph nodes. CT should also be used to assess the chest, a common site of metastases.
Magnetic resonance imaging (MRI) is an excellent modality for assessing the renal vein and vena cava if the sonogram is unclear. MRI is also highly sensitive for nephroblastomatosis, which, if present in the contralateral kidney, may alter management.