Inverted papilloma: urothelial tumor of benign biologic potential.

The inverted papilloma has several classic gross anatomic features. The tumor may be pedunculated or sessile with a characteristic smooth surface. A diameter of up to 3 inches has been noted. The fronds of this exophytic tumor are directed inward thereby simulating invasion of the lamina propria. However, there is a thick basement membrane which surrounds each of the inverted epithelial advancing fronds. The surface of the tumor is covered with a variegated urothelial surface which may be normal, atrophic, or hyperplastic. The bulk of the tumor is made of cords and sheets of well-differentiated urothelium of varying thickness. The epithelium is attached to the surface urothelium and appears to be derived from it. There is a relatively scant amount of fibrovascular stroma interposed between the urothelium. Present intermittently are intraepithelial cysts not unlike that observed in Brunn’s nests. The outer layer of these cysts is usually cuboidal in shape. When examined by light microscopy, the tumor cells are characteristically regular with an absence of mitosis and intercellular bridges between the cells. A case was recently seen at this institution and is histologically illustrated here. The patient was a forty-five-year-old white female who presented with a chief complaint of hematuria of one year’s duration. A freshly voided urine specimen was submitted for urinary cytology, and atypical to suspicious cells were noted that were suggestive of papilloma or early transitional cell epithelioma (Fig. 1A). At cystoscopy the patient was noted to have an exophytic tumor. The surrounding urothelium was also slightly irregular, and a biopsy was taken of this area. The histologic evaluation revealed a proliferation of the urothelium into the underlying fibrovascular stroma (Fig. 1B to D). They are in the form of anastomosing sheets and cords of benign-appearing urothelial cells which do not demonstrate any pleomorphism or anaplasia. Several mitoses were noted throughout various areas of the urothelium. Some cystlike areas were also seen that are similar in cytologic architecture to Brunn’s nests (Fig. 1C and D). Sections of the specimen were placed in a balanced sterile salt solution for special radioautography studies whereas other portions of the same specimen were left in the cystoscopy fluid. Extreme variation in the structural integrity of the specimens can be noted. The specimen was in filtered water for several minutes before it was fixed in 5 per cent formalin solution. It demonstrated swelling and vacuolization of the cytoplasm and the nuclei (Fig. 2B and D). The portion of the specimen that was in the balanced sterile salt solution did not exhibit such cytoplasmic swelling (Fig. 2A and C). Here also there was greater nuclear detail and less swelling of the nuclei (Fig. 2C). Electron microscopy of the balanced salt solution reveals intact structural integrity of the cytoplasmic components such as the mitochondria and Golgi apparatus. There was ultrastructural ballooning and swelling of many of the cytoplasmic structures in the cells obtained from the filtered water solution. Again, this stresses the validity of obtaining tissue in an osmotic solution when the cytologic integrity must