Cystic nephromas (CNs) are uncommon benign renal neoplasms affecting children. The existence of clinical, morphological and genetic differences between pediatric and adult CN, supports an independent classification. The presence of cystic nephroma in a child or young adult should alert the clinician to the possibility of a germline mutation in DICER1.

Almost exclusively occurs in children younger than 4 years old, most of whom are boys with DICER1 syndrome manifestations OMIM: 60120.^1,2  However, 10% to 20% appears to arise de novo.

Palpable relatively well circumscribed large unilateral abdominal mass incidentally found, but familial forms may present bilaterally.³

Poorly encapsulated mass .⁴

Well delineated, multilocular exclusively cystic neoplasm with absence of immature nephrogenic elements, and variation in septal thickness, variation in cyst size and shape, and degree of pericystic stromal condensation.⁴

Diffuse stromal immunoreactivity for estrogen.⁵

Resection with excellent prognosis if completely excised .

DICER1 mutations in 90% of CN cases , either resulted in premature truncation of the DICER1 protein (deleterious truncating mutations) or involve specific amino acids in the RNase IIIb domain including insertion-deletions with frameshifts, nonsense mutations .^4-7  DICER1 mutations have not been found in cystic partially differentiated nephroblastoma. ⁶