The attached photomicrographs show the classic histopathology of renal medullary angiitis, 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. Differentiation from acute tubulointerstitial nephritis is essential considering the very disparate etiologies, treatment, and prognosis. Medullary angiitis is most commonly seen in association with ANCA-associated disease but it has also been described in IgA nephropathy as well as in patients on antibiotics in the setting of infection (see ref below). It is an important lesson to recognize as it may be the only clue in an otherwise inadequate renal biopsy (medulla only) suggesting the presence of a systemic vasculitis.
Hendricks AR1, Harris AA, Walker PD, Larsen CP. Renal medullary angiitis: a case series from a single institution. Hum Pathol. 2013 Apr;44(4):521-5.
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