Cystic nephromas, previously known as multilocular cystic nephromas, are rare benign renal neoplasms classically occurring in adult females in the 4th and 5th decades. As of the 2016 WHO classification, they are considered distinct from pediatric cystic nephromas which have associated DICER1 gene mutation 10,11,14.
Evolving terminology regarding cystic nephromas and other cystic renal tumors reflects ongoing changes in classification, in step with shifting understanding of the disease processes and genetic aberrations.
Classically, cystic nephromas were thought to occur in a bimodal age distribution, affecting young children and adults in middle age. The generic term "multilocular cystic renal tumor" was sometimes used for either cystic nephroma or cystic partially differentiated nephroblastoma, as they were indistinguishable except by microscopic analysis.
More recently, it has been established that the lesions arising in children are distinct from adult cystic nephromas on both immunohistochemical and genetic bases, and are separately categorized by WHO as pediatric cystic nephroma 10,11,14.
As of 2016, the WHO classifies cystic nephroma within the mixed epithelial and stromal tumor (MEST) family along a spectrum of disease 10,13,14.
- overall rare
- adult (typically in the 5th - 6th decades)
- females are predominantly affected
- abdominal pain 12
- palpable abdominal mass 12
- asymptomatic - incidentally discovered on imaging
Grossly, multilocular cystic renal tumors are typically unifocal multiloculated cystic masses surrounded by a thick fibrous capsule and compressed parenchyma 8. Calcification, hemorrhage, and necrosis are unusual.
Microscopically, these tumors are lined by flat, cuboid, or hobnail cells 8, while the fibrous septa may contain mature tubules 3.
Multilocular cystic renal tumors generally have the appearance of a multilocular cystic encapsulated mass on most modalities.
May present as a large abdominal mass displacing and effacing adjacent bowel loops.
- multilocular cystic mass originating from kidney 4
- claw or beak-shape of adjacent renal parenchyma (claw sign) may help confirm a renal origin
- cyst contents usually anechoic, but low-level echoes may be seen
- septal vascularity can also be seen 8
- multilocular cystic mass often herniates into the renal pelvis
- variable septal enhancement
- no nodular or solid enhancement 8
- +/- associated streakiness in perirenal fat 4
Signal characteristics include:
- T1: variable signal, depending on the protein or blood products of the cysts
- T2: hyperintense (cysts)
- T1 C+ (Gd): septal enhancement may be seen
Treatment and prognosis
Radical or partial nephrectomy is usually done, with lymph node excision.
Cystic nephroma is indistinguishable from multilocular cystic renal neoplasm of low malignant potential, formerly multilocular cystic renal cell carcinoma 15.
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