Exploring beyond the typical Wilms tumor: What a radiologist needs to know

Wilms tumor is the most common pediatric renal neoplasm. The diagnosis of Wilms tumor is made on imaging when the radiological features and age of presentation are typical. Percutaneous biopsy is reserved for cases with atypical imaging appearance or older age at presentation, as the biopsy itself upgrades Wilms tumor to stage III. This is more relevant when it comes to the International Society of Pediatric Oncology (SIOP) guideline, which states that chemotherapy should be given before surgery, when compared to the Children's Oncology Group (COG) guideline, which recommends surgery, without neoadjuvant chemotherapy for the initial stages. Few uncommon renal neoplasms may have typical imaging and clinical characteristics, which can help to differentiate them from Wilms tumor. While upfront nephrectomy or nephron-sparing surgery can be done for small masses confined within the kidney and non-aggressive or benign histological types, preoperative chemotherapy with or without biopsy is required for most atypical renal neoplasms. Pseudomasses can mimic atypical renal tumors, but with a few distinguishing imaging features. This review describes the atypical imaging appearances of Wilms tumor and the typical imaging appearance of uncommon renal neoplasms and pseudomasses.