Kidney cysts and tumors often are identified during imaging for unrelated issues. Kidney cysts can be attributable to heritable polycystic kidney diseases. These cysts are rare in children. In adults, they affect approximately 50% of individuals older than 50 years. Kidney cysts are categorized on imaging using the Bosniak Classification of Cystic Renal Masses, which determines the likelihood that cysts are malignant or benign. Asymptomatic Bosniak class I and II cysts require no further evaluation or follow-up; however, symptomatic large simple cysts might require treatment. Bosniak class III and IV cysts might be malignant and require excision. Kidney tumors also occur in children and adults. In children, the most common is Wilms tumor, but after age 10 years renal cell carcinoma (RCC) is more common. In adults, kidney tumors may be malignant or benign. RCC accounts for 85% of kidney tumors in adults, often with metastatic disease. In patients with kidney tumors, biopsy typically is avoided to prevent spread of malignant cells. Tumors that appear suspicious for cancer on imaging are managed directly, which can include total or partial nephrectomy, ablation therapy, and adjuvant therapies, along with chemotherapy and radiotherapy depending on tumor stage. For some patients, evaluation may involve consideration of genetic testing for hereditary cancer syndromes. Patients with these syndromes should undergo periodic screening for RCC.

Case 2. RG is a 55-year-old patient who comes to your office for a follow-up visit after evaluation in the emergency department for abdominal pain. He underwent computed tomography (CT) of the abdomen and pelvis. No cause of the pain was identified, and he was diagnosed with chronic constipation and treated appropriately. However, 7-cm right and 5-cm left kidney cysts were found incidentally on CT. RG has normal kidney function and no history of kidney disease or cancer.