Inverted papilloma of the bladder: observation of 3 clinical cases and discussion on their clinico-pathologic characteristics.

Three cases of urothelial inverted papilloma, detected in two female patients aged 32 and 31 years, respectively and in one 67-year-old male patient, are described. Inverted papilloma is a benign lesion which occurs in the urinary epithelium with a 20% incidence in comparison with other urothelial tumours. The male:female ratio is 3:1. The histological structure of urothelial inverted papilloma is similar to that of inverted papilloma of the nasal and paranasal sinuses. It presents interanastomosed epithelial cords, with transitional cells, which develop in the tunica propria connective tissue. Some cells are distributed in such a way as to constitute vacuolated glandular-like structures. The histogenetic origin of the lesion from Home subtrigonal or Albarran subcervical glands is debatable. Recent aetiological hypotheses have claimed that the origin of the lesion may be related to Brunn's nest hyperplasia and/or to chronic urothelial inflammation. The latter hypothesis would currently appear to be the most accredited: immunostaining for cytokeratins would tend to support a urothelial inflammatory aetiology. In our cases, we achieved a definitive diagnosis of inverted papilloma only at histology, because of the specificity of the echotomography and cystoscopy findings. Urinary cytology revealed only a large number of inflammatory cells with anaplastic elements, but without any more detailed morphological description. We performed a transurethral resection of the bladder (TURB) in all three patients: routine follow-up showed the absence of inverted papilloma relapses. On the basis of the above-mentioned data and a thorough review of the literature, we attempt to assess and classify the clinico-pathological findings and the aetiological hypotheses of urothelial inverted papilloma. In addition, the benign nature of the lesion and any malignant transformation factors are discussed.