Predisposing factors include pregnancy, diabetes, urinary calculi, prior instrumentation (e.g., cystoscopy), chemotherapy or radiation therapy. Cystitis may be classified as acute or chronic. Histologically such lesions show nonspecific signs of acute or chronic inflammation. Malakoplakia is a unique form of chronic cystitis in which the infiltrate consists of macrophages that contain cytoplasmic inclusions known as Michaelis-Gutmann bodies. Chronic interstitial cystitis is a persistent form of chronic cystitis of unknown etiology, that does not respond to conventional antibacterial therapy and is often associated with mucosal ulceration (Hunner ulcer).