Nephrogenic adenoma: report of a case and review of morphologic mimics.

Nephrogenic adenoma, also referred to as nephrogenic metaplasia, is an uncommon benign lesion of the urothelial tract, characterized by a circumscribed proliferation of tubules, cysts, and papillae lined by cells with low cuboidal to columnar epithelium. The diagnostic features that are useful in the recognition of this benign entity are the characteristic mixture of various architectural patterns, associated stromal edema and inflammation, hyaline sheath around tubules, eosinophilic colloidlike secretion within tubules, and lack of mitotic activity. Nephrogenic adenoma can be a significant diagnostic pitfall as certain histologic features, such as the presence of enlarged nuclei with prominent nucleoli, degenerative nuclear atypia, tiny tubules with blue mucin simulating signet ring cells, and focal invasion into superficial muscle, when taken out of context, can mimic malignancy. Herein, I report a case of nephrogenic adenoma with some worrisome histologic features and review the diagnostic criteria as well as pertinent morphologic malignant mimics of nephrogenic adenoma.