[Clinical studies on inverted papilloma of the urinary tract]

Inverted papilloma of the urinary tract is believed to be a benign neoplasm based on its histologic morphology and clinical behavior. In recent years, however, several investigators have warned against too optimistic an approach, emphasizing the possibility of malignant cellular transformation within the lesion, or its eventual association with other urothelial tumors such as transitional cell carcinoma or carcinoma in situ. We here report on 35 clinicopathologically diagnosed cases of inverted papilloma, and present the clinical significance attributed to these lesions in view of the current literature.

From 1976 to 1997, 35 cases of inverted papilloma of the urinary tract were treated at our hospital. This report presents the clinical features of these cases, the results of prognosis research, an investigation of the cases in which inverted papilloma and transitional cell carcinoma were found to co-exist, and a discussion of the recurrent cases of inverted papilloma found in previous literature.

The patients ranged from 24 to 77 years of age, with a mean of 54 years, and included 4 women and 31 men. The most frequently occurring symptom was grosshematuria, and more than 90% of the 35 cases occurred in the bladder. In 2 of the 35 cases, transitional cell carcinoma coexisted with the inverted papilloma, at a different location in the bladder in one case and within the same neoplasm in the ureter in the other case. Clinical courses after treatment were followed in 29 of the 35 cases, with a follow-up period of from 8 months to 19 years (mean follow-up, 5 years and 4 months). Of these 29 cases, 2 showed recurrence, one at 16 and one at 30 months after the initial resection. Many previous reports show that the association of inverted papilloma and transitional cell carcinoma is stronger in the upper urinary tract and recurrence of inverted papilloma almost always happens with 2 years.

This study suggests that some cases of urinary inverted papilloma show recurrence or malignant potential. Our results indicate that all cases of urinary inverted papilloma should be treated and followed as cases of low-grade transitional cell carcinomas. Consequently, all cases must be followed for two years or more after the initial operation.