polypoid cystitis
Polypoid cystitis and its more chronic phase papillary cystitis, which results as a reaction to injury to the bladder mucosa, is a benign lesion mimicking various papillary urothelial neoplasms.
Analogous lesions occur throughout the urothelial tract and are referred to as polypoid urethritis, polypoid ureteritis, and polypoid pyelititis when present in the urethra, ureter, and renal pelvis, respectively.
The key to correctly diagnosing polypoid/papillary cystitis is to recognize at low magnification the reactive nature of the process with an inflamed background that is edematous or densely fibrous with predominantly simple, non-branching, broad-based fronds of relatively normal thickness urothelium, and not focus at higher power on the exceptional frond that may more closely resemble a urothelial neoplasm either architecturally or cytologically.
In cases where the diagnosis of papillary neoplasia is not straightforward and there is a question of polypoid cystitis, pathologists should seek clinical history that might suggest a reactive process.
Because the urologist can more often better recognize the inflammatory nature of the lesion than the pathologist, the pathologist should hesitate diagnosing urothelial neoplasia when the cystoscopic impression is that of an inflammatory lesion.
References
Lane Z, Epstein JI. Polypoid/papillary cystitis: a series of 41 cases misdiagnosed as papillary urothelial neoplasia. Am J Surg Pathol. 2008 May;32(5):758-64. PMID: 18379418