**1. Introduction**

Interstitial cystitis/bladder pain syndrome (IC/BPS) is a condition characterized by chronic pelvic pain, pressure or discomfort perceived to be related to the urinary bladder and is accompanied by other urinary symptoms in the absence of confusable diseases [1]. Interstitial cystitis was first described by Skene in 1887, and its definition has changed over the past 100 years. Guy Hunner was the first to identify the characteristic cytoscopic findings associated with bladder pain that were initially called Hunner's ulcers. However, these cytoscopic findings are not characteristic of an ulcer and instead due to a severe inflammatory lesion; therefore, the term ulcer is no longer used. IC/BPS is divided into the Hunner type interstitial cystitis with Hunner lesion and bladder pain syndrome (BPS) without Hunner lesion [2]. Hunner type IC/BPS cystitis has characteristic endoscopic findings and distinct inflammatory histopathology, whereas BPS lacks both the endoscopic and histopathology findings. The Hunner lesion is described as a "circumscript, reddened mucosal lesion with small vessels radiating toward a central scar, with fibrin deposit or coagulum" and a "velvet red patch that looks like carcinoma in situ" (**Figure 1**) [1].

During cystoscopic examination, it is crucially important to watch the bladder mucosa from the early phase of bladder filling, because Hunner lesions might be obscured shortly after bladder distension. Recent research has revealed significant differences in the demographics, clinical presentation, bladder pathology, urinary marker profiles, and treatment responses between patients with IC/BPS with

**Figure 1.** *Cystoscopic findings of Hunner lesion.*

Hunner lesion and those without Hunner lesion. IC/BPS with Hunner lesions is a distinct inflammatory disorder characterized by epithelial denudation and frequent clonal expansion of infiltrating B cells, in association with biological processes involved in immune responses and infectious disease [3]. IC/BPS without Hunner lesions, however, rarely show histological changes and retain a preserved urothelium. IC/BPS with Hunner lesion has an incidence of up to 7% among IC/BPS patients and is categorized as a separate disease from non-Hunner IC/BPS [2, 4, 5]. In this chapter, we discuss intravesical treatment and endoscopic treatment of the Hunner lesion type IC/BPS.
