Malakoplakia is regarded as a chronic granulomatous infl ammatory disease with a good prognosis. It usually aff ects the urinary system, especially the urinary bladder. Bacterial infections, including E. coli are thought to be the main factor in pathogenesis. It frequently coexists with chronic diseases and immunosuppression state. Histopathological examination of aff ected tissue samples is thought to be the best diagnostic method. Th e basic microscopic feature is mixed infl ammatory infi ltration containing foamy histiocytes known as von Hansemann cells, frequently with basophilic inclusions known as Michaelis-Gutmann bodies. Symptoms and the clinical course of malakoplakia depend on location and the extent of the lesions. Th e lesion is treated successfully with antibiotic therapy and surgical excision.

Pigmented villonodular synovitis (PVNS) is a benign disease that rarely undergoes malignant transformation. Th ere are two types of disease: localized (nodular tenosynovitis) and diff used (pigmented villonodular synovitis/tenosynovitis) with intra- or extra-articular locations. Th e second one is limited to synovium of the burse (PVNB) or tendon sheath (PVNTS). Th e intraarticular lesions are usually located in the knee, hip, ankle and elbow joints. Histologically, PVNS is a tenosynovial giant cell tumor, characterized by proliferation of two types of mononuclear cells — predominantly small, histiocyte-like cells and larger cells with dense cytoplasm, reniform or lobulated nucleus, with accompanying multinucleated giant cells and macrophages overloaded with hemosiderin that give typical image on MRI — currently selected as a gold standard for its diagnosis. Th e classic X-ray and CT are non-specifi c but similar to ultrasound should be used to evaluate disease progression and treatment response if radiotherapeutic and pharmacological methods were selected for treatment. An open arthroscopic surgery could also be applied in selected cases.