Polypoid cystitis

What is polypoid cystitis?

Polypoid cystitis is a non-cancerous and reversible condition caused by chronic (long-standing) inflammation on the inside of the bladder. Pathologists use the word, polypoid, to describe an abnormal growth that sticks out from the surface of the tissue, and the term, cystitis, to describe inflammation on the inside of the bladder.

The bladder and ureters

The bladder is a hollow organ located in the pelvis. The purpose of the bladder is to store urine and then release it out of the body through a tube called the urethra. Urine is made in the kidneys and travels to the bladder by two long tubes called ureters.​

The inside of the bladder is lined by cells called urothelial cells. These cells form a barrier on the inner surface of the bladder called the urothelium. The inside of the ureters and urethra are also lined by urothelial cells. The tissue directly below the urothelium is called the lamina propria. Together, the urothelium and lamina propria form a thin layer of tissue called the mucosa.

What causes polypoid cystitis?

Polypoid cystitis most commonly results from injury caused by urinary catheters. The frequency and severity of polypoid cystitis increases with the duration of catheter use. Polypoid cystitis can also be caused by other conditions that injure or irritate the inner lining of the bladder, including vesical fistulas, kidney stones, and radiation therapy. Treatment, if required, typically involves the removal of the irritating factor.

How is polypoid cystitis found and diagnosed?

Your doctor may suspect that you have polypoid cystitis if you have a history of catheter use, radiation to the pelvis, or another injury to the bladder, and if you are experiencing pain when urinating, the inability to completely empty your bladder, or have blood in your urine. Imaging studies such as an ultrasound or CT scan may be performed to better visualize the bladder.

When seen on imaging studies of the bladder (such as an ultrasound or CT scan) polypoid cystitis may look like a mass and mimic the appearance of bladder cancer. As a result, your doctor may also recommend a procedure called cystoscopy, which uses a small camera attached to a narrow tube to see the inside of the bladder. During the cystoscopy, a small sample of tissue can also be removed in a procedure called a biopsy. The tissue sample is then sent to a pathologist who examines it under the microscope.

How do pathologists make the diagnosis of polypoid cystitis?

When examined under the microscope, the urothelial cells in polypoid cystitis may appear normal, or mildly crowded. Pathologists describe an increased number of cells as hyperplasia. The urothelium may also be growing as long projections, which pathologists describe as fronds. The fronds of tissue may have a broad or narrow base and may appear as a single projection, or multiple branching projections.

The stroma (tissue directly below the urothelium) also shows a number of changes that are characteristic of polypoid cystitis. For example, specialized immune cells are typically seen in the stroma. Other signs of chronic inflammation such as edema and fibrosis are also commonly visible. Finally, a non-cancerous change called metaplasia may also be seen. Metaplasia is a word pathologists use to describe cells that have changed from one specialized type of cell to another.

polypoid cystitis

Your pathologist will carefully examine the tissue sample in order to rule out other conditions that may look similar to polypoid cystitis. The most important condition to rule out is papillary urothelial carcinoma, a type of bladder cancer. When examined under the microscope, most of the cells in polypoid cystitis have only a single nucleus per cell. The nucleus is the part of the cell that holds genetic material, and all of the nuclei—the plural for nucleus—should be approximately the same size and shape. In contrast, the cells in urothelial carcinoma commonly have more than one nucleus per cell and the nuclei vary greatly in size and shape.

Pathologists use the term ‘multinucleated’ to describe cells with more than one nucleus, and pleomorphic to describe nuclei that vary greatly in size and shape. Because cancer cells divide faster than normal cells, your pathologist will look to see how many cells are dividing. The process of cell division is called mitosis and a cell that is in the process of dividing is called a mitotic figure. Mitotic figures can be seen in polypoid cystitis; however, a far greater number will be seen in urothelial carcinoma. Looking for these features allows your pathologist to recognize that the changes seen under the microscope are of polypoid cystitis and not urothelial carcinoma.

Additional resources

  • Humphrey P. Polypoid/Papillary Cystitis. J Urol 2013; 189: 1091–2.
  • Lane Z, Epstein JI. Polypoid/papillary cystitis: A series of 41 cases misdiagnosed as papillary urothelial neoplasia. Am J Surg Pathol 2008; 32: 758–64.
  • Ekelund P, Anderström C, Johansson S, Larsson P. The reversibility of catheter-associated polypoid cystitis. J Urol 1983; 130: 456–9.
  • Ekelund P, Johansson S. Polypoid cystitis: a catheter-associated lesion of the human bladder. Acta Pathol Microbiol Scand A 1979; 87A: 179–84.
  • Kwok J-L, Eng M, Urol F. Polypoid Cystitis and Bilateral Hydronephrosis Mimicking Urothelial Carcinoma. DOI:10.1089/cren.2018.0098.
  • Young RH. Tumor-like lesions of the urinary bladder. Mod Pathol 2009; 22: S37–52.
By Elena Pastukhova, BSc, and Trevor Flood, MD FRCPC
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