Transitional cell papilloma was not favored because, unlike this lesion, papillomas are primarily epithelial and have fine fibrovascular stalks. Fibromas of the bladder are often pedunculated, contain variable numbers of eosinophils, are covered by a hyperplastic epithelium that may be eroded or ulcerated, and are occasionally associated with calculi. However, unlike this lesion, fibromas are sharply demarcated from the preexisting tissue. Squamous metaplasia is multifocally present in some sections. Epithelial neoplasms not previously mentioned include adenomas, carcinomas and adenocarcinomas.
Adenomas arise from mucous glands or areas of mucous metaplasia.
Carcinomas are subclassified as transitional cell, squamous cell, undifferentiated or adenocarcinoma. Carcinomas may produce papillary growth into the lumen, infiltrate the wall of the bladder, or remain in situ within the mucosa. Papillomas may be inverted and must be differentiated from invasive carcinoma. Mesenchymal neoplasms of the urinary bladder include benign and malignant tumors of fibrous tissue, smooth and skeletal muscle, and vascular histogenesis. Palmer N eds.