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Background
There are quite a few renal lesions in the pediatric age group that might mimic a renal neoplasm on imaging but may be proven on biopsy to be a wrong radiologic diagnosis. This presentation attempts to describe the pediatric renal pseudotumors that a radiologist needs to keep in mind when reporting these lesions with similar imaging characteristics.

Educational Goals / Teaching Points
There are multiple differentials to be considered when a renal mass is encountered in the pediatric age group. The most common renal neoplasm in children less than 8 years is a Wilms tumor. The differentials include other malignant neoplasms like nephroblastomatosis, benign neoplasms like mesoblastic nephroma, multilocular cystic nephroma, angiomyolipoma, and metastatic diseases like neuroblastoma, leukemia, and lymphoma. However, there are lesions that mimic a renal neoplasm on imaging but may not be proven on biopsy to be a wrong radiologic diagnosis. The term "renal pseudotumor" was defined first by Felson and Moskowitz to describe a real or simulated renal mass resembling neoplasm on imaging, but histologically consisting of normal renal parenchyma. The term is also broadly used to designate a multitude of normal and benign lesions of the kidney. More common lesions like abscesses and infection may be diagnosed confidentially, but atypical or uncommon presentations do occur and may result in unwanted interventions.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Ultrasound is usually the initial mode of imaging for evaluating the kidneys. CT and MRI are only used for further characterization of a nonspecific finding identified on ultrasound. Sometimes even CT or MRI may be inconclusive, and a biopsy might be needed for diagnosis. Etiology of renal pseudotumors in the pediatric age group may be categorized as anatomic variants, infection, vascular, granulomatous, and miscellaneous causes including anatomic variants (hypertrophied columns of Bertin, dromedary hump, crossed fused renal ectopia), infection (pyelonephritis, renal abscess), vascular (renal Infarction, lymphatic malformation), granulomatous (sarcoidosis, medications [NSAIDs, antibiotics], infections (mycobacterial, fungal, bacterial, and viral), idiopathic) and miscellaneous (acute kidney injuries).

Conclusion
Focal renal pseudotumors in pediatric patients can result from normal anatomic variants, infection, lymphatic malformation, granulomatous inflammation, and acute renal injury. These have to be kept in mind when reporting these lesions. Imaging plays an integral part in the diagnosis and further workup; however, sometimes imaging may be inconclusive, and a biopsy might be ultimately needed for diagnosis.