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Diagnosis: Multilocular Cystic Nephroma (or Adult Cystic Nephroma)

Multicystic nephroma (MCN) is a rare, benign cystic neoplasm of the kidney. This tumour has been variously described as cystic nephroma, multilocular cystic tumor, renal multilocular cyst, multilocular cystic nephroma, renal cystadenoma and partial polycystic kidney (Sharma A, et al. Asian J Urol. 2017;4:128-130. [PubMed link]).

It was first described in 1892 as cystic adenoma of the kidney. Its etiology and histogenesis is debatable, and in the past they were considered to be developmental lesions with malignant potential. The name multicystic nephroma was first proposed in 1951 and later modified and further subdivided into cystic nephroma and cystic partially differentiated nephroblastoma depending on the absence and presence of blastemal element, respectively. MCN is an uncommon, benign cystic lesion of the kidney with bimodal age distribution, occurring in both infants and adult population. Although it has been described in neonates, MCN is more commonly seen in the age group of 2–4 years (of which 73% are in males). In adults, it is seen in the 4th–6th decade with its male to female ratio being 1:7. Adult-onset cystic nephroma is histogenetically and morphologically different from pediatric cystic nephroma. According to the World Health Organization (WHO) classification of renal neoplasms (2016), MCN is grouped with the mixed epithelial and stromal tumors (MEST). The term "mixed epithelial and stromal tumour family" is used in the WHO classification to encompass both adult MCN and MEST; in this classification, the pediatric cases are named: "paediatric cystic nephroma" and the cases in adults: "adult cystic nephroma" (Moch H, Humphrey PA, Ulbright TM, Reuter VE [Eds]: WHO Classification of Tumours of the Urinary System and Male Genital Organs (4th edition). IARC: Lyon 2016). Adult cystic nephromas are localized, well-circumscribed, multilocular tumours with non-communicating cysts lined by hobnail columnar or flattened epithelium. The septa consist of fibrous stroma, often with areas of cellular condensation reminiscent of ovarian stroma. MEST typically occur in perimenopausal women, with a mean patient age of 52 years. MCN and MEST are described collectively in the WHO classification as if they were the same tumor.

Paediatric cystic nephroma is a distinct entity. It is composed entirely of cysts separated by septa. The cysts are lined by flattened, cuboidal. or hobnail epithelium, or are denuded. The septa contain fibrous tissue with focal cellular condensations and well-differentiated tubules. The presence of immature nephroblastic elements excludes the diagnosis of paediatric cystic nephroma and indicates cystic partially differentiated nephroblastoma (Moch H, Humphrey PA, Ulbright TM, Reuter VE [Eds]: WHO Classification of Tumours of the Urinary System and Male Genital Organs (4th edition). IARC: Lyon 2016).

Surgical intervention is the effective method at present to exclude malignant cystic lesions of kidney. However, nephron-sparing surgery can be an option depending on the site and size of the lesion (Wilkinson C, et al. Adult multilocular cystic nephroma: Report of six cases with clinical, radio-pathologic correlation and review of literature. Urology Annals. 2013;5(1):13-17. [PubMed link]).

See the chapter: Renal Neoplasms of our Tutorial (only Spanish version).

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