Kidney Biopsy Teaching Case: Medullary Angiitis in the setting of Pauci-Immune Crescentic Glomerulonephritis

Almost all pathological diagnoses made from a native kidney biopsy come from careful examination of the renal cortex. In fact, a good biopsy specimen contains little medulla. It is important, to remember, however, that certain diseases have a characteristic medullary component. Medullary angiitis has histological features of interstitial hemorrhage in the medulla with an associated polymorphonuclear leukocyte infiltrate and surrounding karyorrhectic debris. These findings are primarily found in the setting of antineutrophil cytoplasmic antibody (ANCA)-associated disease. Increased awareness of this pathologic finding is needed, as these histologic findings can be misdiagnosed as interstitial nephritis alone, missing accurate diagnosis and appropriate subsequent management. Medullary angiitis identified in the setting of negative immunofluorescence is most suggestive of pauci-immune crescentic glomerulonephritis.