Squamous papilloma is a rare benign neoplasm seen in the bladder. It is composed of papillary cores with overlying histologically benign squamous epithelium. [1, 2] It is unclear whether squamous papilloma represents the squamous counterpart of urothelial papilloma.
The risk factors for squamous papilloma are similar to those for other urothelial neoplasms; cigarette smoking and occupational exposure to aromatic amines are among the most important. Specific epidemiologic studies on squamous papilloma are lacking. [1, 2]
Squamous papilloma has not been reported to have a predilection for a specific location in the bladder. Most cases arise in the dome, the lateral or posterior walls, or the bladder neck. The lesion may occur in the urethra. 
Clinical Features and Imaging
Squamous papilloma most frequently occurs in elderly women. The disease follows a benign clinical course. Recurrences are uncommon. Irritative symptoms and hematuria may occur. 
Squamous papilloma is a DNA-diploid lesion; it tests negative for HPV DNA. 
Tumor Spread and Staging
Prognosis and Predictive Factors
Squamous papilloma is a benign tumor that may rarely recur but does not progress. Some patients may in time develop bladder cancer.  In a recent study that included 5 patients with squamous papilloma, 1 patient had low-grade urothelial carcinoma at cystectomy after an interval of 21 months (low-grade urothelial carcinoma preceded the diagnosis of squamous papilloma); 2 patients were free of lesions on follow-up biopsy. Two cases were lost to follow-up.