What is the diagnosis?

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Diagnosis

Multilocular Clear Cell Renal Cell Carcinoma

Discussion:

Clear cell renal cell carcinomas account for approximately 60-70% of all cases of renal cell carcinoma. They are believed to arise in the epithelial cells lining the proximal tubule. Patients in all age groups are at risk for its occurrence; however, the greatest majority occur in patients over 40 years of age, the majority of whom are males (1.5:1).

Multilocular cystic renal cell carcinoma (also known as multicystic clear cell carcinoma) is a rare cystic tumor of the kidney that has a good clinical outcome. It was considered a distinct subtype of clear cell renal cell carcinoma in the 2004 WHO classification of renal tumours. It is an uncommon tumor of the kidney, composed of multiple cysts with clear cells in the septa, indistinguishable from grade 1 renal cell carcinoma. It constitutes about 105% of all renal cell carcinomas. There is a male preponderance (2-3:1), with occurrence at age 20-76 years; majority of whom are in their 50’s or 60’s. Females tend to present at a younger age than males.

Most patients are asymptomatic, and their tumors are discovered incidentally. Only a minority have either a palpable mass, gross hematuria, abdominal or back discomfort or rarely, systemic symptoms. Imaging typically demonstrates a complex cystic mass.

Grossly, multilocular cystic renal cell carcinomas range from 0.5-13.0cm in size. They are typically unilateral, and solitary well circumscribed masses composed entirely of cysts, separated from the renal parenchyma by a fibrous wall. The cysts themselves are variable in size, and contain clear or hemorrhagic fluid. Necrosis is absent, and there are no grossly visible nodules expanding the septa. This is a key feature that differentiates the tumor from extensively cystic conventional clear cell renal cell carcinoma.

Histologically, the diagnostic criteria consists of: cysts lined by cuboidal, epithelial cells, usually as a single layer, but occasionally multilayered, and can form minute papillary structures, and fibrous septa with clusters of epithelial cells with clear cytoplasm within the septa.

There have been no reports of recurrence or metastasis of multilocular cystic renal cell carcinoma. They are by definition of low nuclear grade and have shown extension beyond the kidney into the perirenal fat in rare cases. Surgical resection is indicated to exclude extensively cystic clear cell renal cell carcinoma. Trichoepithelioma are regarded as poorly differentiated hamartomas of the skin adnexae. There are three variants: Solitary, multiple and desmoplastic. Solitary and multiple share the same histological features, whereas desmoplastic differs not only in histology, but is considered a separate clinicopathological entity.

• Bostwick et al. (2008).Urologic Surgical Pathology: 2ed. Mosby Elsevier
• Suzigan et al. (2006). Multilocular cystic renal cell carcinoma: A report of 45 cases of a kidney tumor of low malignan potential. Am J Clin Pathol, 125, 217-222.