Inverted papilloma of urinary bladder. Scanning and transmission electron microscopic observation

IS SURVEILLANCE NECESSARY FOR INVERTED PAPILLOMA IN THE URINARY BLADDER AND URETHRA?

BACKGROUND

A case series of inverted papilloma of the urinary bladder and urethra is presented, together with a review of the literature with respect to multiplicity, recurrence rate and association with transitional cell carcinoma, and a discussion on surveillance of the lesion.

METHODS

Cases of inverted papilloma of the lower urinary tract in a single centre were reviewed. Patient and tumour characteristics, recurrence and associated transitional cell carcinoma are reported.

RESULTS

Twenty patients were included (18 male, two female). The mean age was 60.8 years (range 35-78 years). All had solitary tumours ranging from 3 mm to 30 mm in size. Median cystoscopic follow up was 30 months (range 2-140 months). There was no recurrence. One patient was associated with subsequent transitional cell carcinoma 44 and 76 months later. Together with the present 20 cases, review of the English literature with respect to inverted papilloma of the lower urinary tract identified a total of 322 cases reported, with a recurrence rate of 3.85%. Moreover, 1.55%, 5.90% and 1.54% were associated with previous, simultaneous and subsequent transitional cell carcinoma, respectively.

CONCLUSIONS

Recurrence is not uncommon and risk of subsequent transitional cell carcinoma is not rare, such that non-invasive surveillance with flexible cystoscopy is recommended for inverted papilloma of the lower urinary tract.

Inverted papilloma of bladder: clinical significance

Based on 15 cases of inverted urothelial papilloma, we present the clinical significance of these lesions in view of the current literature. An inverted papilloma should raise suspicion with respect to the whole urothelial surface. However, approaching every lesion of this type as a (pre-)neoplastic tumor does not seem justified, since 90 percent of all cases reported so far do not present any clinical or histologic feature of malignancy. Some factors, such as the patient's history, eventually associated urothelial carcinomas, or histologic features of malignant transformation within an inverted papilloma, must be taken into consideration. If no single indication in favor of malignancy has been disclosed, we believe follow-up with yearly endoscopic investigations, in addition to regular urine cytologies, may suffice.

Inverted papilloma: observation with scanning and transmission electron microscopy

Three cases of inverted papilloma of the urinary bladder were studied by transmission electron microscopy. Scanning electron microscopic observation was made in one of these. The surfaces of the outer-most tumour cells were covered with short stubby microvilli. Multiple bud like proliferations of the tumour cells were compatible with a trabecular type of inverted papilloma. The tumour cells of the trabeculum mimicked the intermediate and basal cells of the epithelium which covered the surface. Microcysts are believed to be formed by epithelial migration into pits, creating an epithelial inversion, and do not represent central necrosis. Ultrastructure suggests that inverted papilloma is a very well differentiated tumour.