OFP-12-004 Two cases of ANCA associated vasculitis with geographical necroses in the kidney tissue A. Bartonova * , E. Honsova, R. Rysava * IKEM, Dept. of Pathology, Praha, Czech Republic Objective: ANCA associated vasculitides (AAV) are rare systemic autoimmune diseases affecting small to mediumsized blood vessels. In kidney biopsy samples, AAV usually demonstrate pauci-immune necrotizing crescentic glomerulonephritis (GN). Method: Among 198 cases of AAV evaluated at IKEM during 10 years, 2 had a very unusual pattern of renal involvement. Results: The first patient had been treated for recurrent otitis media with unilateral hearing loss. He also suffered from artralgias and hematuria. An ultrasound study revealed a tumor-like mass in his kidney. During exploratory surgery, the lesion appeared to be infiltrative and a nephrectomy was performed. The second patient presented a granulomatous inflammation in a scar. A month later she developed multiple kidney and spleen "abscesses" with negative hemoculture, and underwent a nephrectomy with splenectomy. In both cases, the final pathological diagnosis was necrotizing granulomatous vasculitis of small and medium-sized vessels, with large geographical necroses of kidney tissue simultaneously with necrotizing crescentic GN. Tests for ANCA antibodies were positive. No microbial pathogens including mycobacteria were detected. Objective: Polyomavirus nephropathy (PVN) is a common complication after renal transplantation. Virus control is achieved by a reduction of immunosuppression allowing an effective T cell-mediated antiviral immune response. The morphology of resolving PVN has not been investigated. Method: 101 protocol biopsies of 34 patients with PV viremia treated by reduction of immunosuppression only were included and scored according to Banff criteria. The extent of interstitial inflammation was estimated as % of cortex. The number of tubular cross sections with SV40+ cells per mm of biopsy length was counted. Findings were grouped as pre-, increasing, decreasing, and post-viremia. Results: During the phase of decreasing viremia, we found a significant increase in the tubulitis score, the extent of tubules with intraepithelial lymphocytes, and interstitial inflammation (p<0.001). These, to a lower extent, persisted after virus clearance. The number of SV40+ tubules correlated with the virus load in the serum, but SV40 immunohistochemistry was frequently negative (33/55 cases), especially if viremia was below 106 geq/ml. Conclusion: Resolving PVN is characterized by a self-limiting acute interstitial nephritis. Our findings are important because the diagnosis of interstitial rejection depends on the same morphological criteria. Therefore, acute interstitial rejection cannot be diagnosed with certainty during PV viremia.