Answer: Nested variant of urothelial carcinoma

Histology: Within the lamina propria of the bladder is a proliferation of small crowded nests of urothelium. The nests are solid without lumina formation. In the intervening stroma between the nests is a lymphoplasmacytic infiltrate. The nests are composed of fairly uniform cells with slightly enlarged nuclei, occasional nucleoli yet lacking nuclear pleomorphism.

Discussion: This biopsy is classic of nested variant of infiltrating urothelial carcinoma. In contrast to von Brunn’s nests, the nests within nested variant of urothelial carcinoma are smaller and more crowded. Furthermore, often there is cyst formation filled with eosinophilic colloid like material within proliferation of von Brunn’s nests within the bladder. Furthermore, at scanning magnification von Brunn’s nests have a non infiltrative appearance with the base of the von Brunn’s nests lining up in a row without irregular proliferation down into the underlying stroma. Although there is a lymphoplasmacytic infiltrate adjacent to the nests of the urothelium in the current case, this not lymphoepithelial like carcinoma. First, lymphoepithelial like carcinoma is characterized by cells with enlarged nuclei and very prominent nucleoli as opposed to the more bland cytology seen in the current case. Furthermore, the lymphocytes within lymphoepithelial like carcinoma tend to be more intermingled within the neoplastic cells as opposed to the intervening stroma as seen in the current case. Nephrogenic adenomas may appear infiltrative yet are not composed of solid nests of cells. Nested variant of urothelial carcinoma despite its bland cytology is an aggressive tumor. In the current case as there was not muscularis propria sampled on the specimen, additional staging transurethral resection should be preformed to look for muscle invasion, especially given the aggressive nature of nested variant of urothelial carcinoma.