Renal medullary angiitis: a case series from a single institution.

Renal medullary angiitis is a lesion involving the vasa recta of the medulla. The characteristic morphologic findings on renal biopsy include interstitial hemorrhage with associated polymorphonuclear leukocyte infiltration and karyorrhectic debris. A total of 18 cases have been described in three publications, all in the setting of antineutrophil cytoplasmic antibody (ANCA)-associated disease. We sought to detail the morphology and clinical significance of this lesion. A total of 38 cases of medullary angiitis were identified in our case files from January 2008 through August 2011. The clinical history was reviewed and pertinent information including patient age, gender, indication for biopsy, serum creatinine, and any positive serologic tests (ANCA) was collected for each biopsy. Cases with known and unknown ANCA status were reported separately. In total, 19 (63%) of 30 cases of medullary angiitis with known ANCA antibody status were ANCA positive, whereas 11 (37%) of 30 were determined to be secondary to other etiologies. The most common non-ANCA etiology of medullary angiitis was immunoglobulin A nephropathy (20%) followed by antibiotic treatment in the setting of infection. In ANCA-unknown cases, 4 (50%) of 8 had pauci-immune crescentic glomerulonephritis. No cases had renal cortex involvement. This is the largest study to date detailing the morphology of medullary angiitis and the first to show medullary angiitis outside the setting of ANCA-associated disease. It is an important lesion to recognize as it frequently suggests the presence of a systemic vasculitis and could be mistaken for interstitial nephritis.