Belongs to the mixed epithelial and stromal tumour (MEST) family: predominantly cystic (adult cystic nephroma) and variably solid (MESTs) containing biphasic epithelial and stromal components with spindle stroma, glands, and cysts.
ICD-O code - 8959/0.
Typically occur in perimenopausal women and related to hormonal imbalance.
Always unilateral.
Gross: Generally, unencapsulated but well circumscribed, with a mean size of 9 cm. Cut surface is cystic with thin clear to opalescent fluid.
Light microscopy: Variable sized cysts lined by flat, cuboidal , hobnail, or (rarely) columnar cells. Focally, Müllerian features can be found. Rarely, pyloric, intestinal or urothelial lining can also be appreciated. The stroma can be hypocellular, myxoid or hypercellular that can show condensation around the epithelial component. Ovarian stroma is often present. Smooth muscle and adipose tissue metaplasia can be encountered.
Treatment: Surgery is usually curative.
Prognosis: Excellent. However, rare malignant transformation of the stromal component can occur that portends a guarded prognosis.
References
WHO Classification of Tumours of the Urinary System and Male Genital Organs [4th edition].
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