Adult and pediatric cystic nephroma: an easily misdiagnosed renal tumor

Background: Cystic nephroma (CN) is a rare, benign renal tumor often misdiagnosed due to overlapping radiological features with simple renal cysts and malignant cystic neoplasms. CN primarily affects boys and adult females. This study aimed to review the clinical, imaging, and pathological characteristics of CN to improve diagnostic accuracy. Methods: A retrospective analysis was conducted on six confirmed CN cases treated at a single institution (2010-2024). Data included demographics, imaging findings (Bosniak classification), surgical approach, histopathology, and immunohistochemistry (IHC). Results: The cohort consisted of two males (one pediatric) and four females. Preoperative imaging, revealing multilocular cystic lesions with septal enhancement, led to a high misdiagnosis rate: five cases (83%) were misinterpreted as simple renal cysts (Bosniak II-III). Surgical interventions included partial nephrectomy (n=3), radical nephrectomy (n=1), and nephroureterectomy (n=1). Intraoperative frozen section analysis in one case was instrumental in confirming the CN diagnosis and guiding radical resection. Histopathology showed multilocular cysts lined by hobnail epithelium. IHC confirmed PAX-8 positivity (4/4) and ER/PR expression (3/4 and 2/4, respectively). Conclusion: CN as a rare benign renal tumor, preoperative differentiation of CN, particularly from benign simple renal cyst, remains difficult. Surgical excision with pathological verification is critical. Intraoperative frozen section analysis aids in determining the surgical approach (nephron-sparing vs. radical resection) for patients with lesions that are difficult to distinguish as benign or malignant prior to surgery. Pathological hallmarks and supporting IHC (PAX-8, ER/PR) remain the diagnostic gold standard.