title: Magnetic resonance elastography noninvasively detects in vivo renal medullary fibrosis secondary to swine renal artery stenosis.
abstract: OBJECTIVE
  Magnetic resonance elastography (MRE) can noninvasively sample tissue stiffness in vivo. Renal fibrosis secondary to renal artery stenosis (RAS), which is aggravated in atherosclerotic RAS (ARAS), may increase its stiffness. An increase in cortical stiffness in vivo can be masked by intrinsic hemodynamic determinants, whereas renal medullary stiffness is less dependent on renal hemodynamics. Therefore, this study tested the hypothesis that MRE-determined medullary stiffness would correspond to the histological degree of medullary fibrosis in stenotic kidneys in RAS and detect its exacerbation in ARAS.
  
  
  METHODS
  Seventeen pigs were studied 10 weeks after induction of unilateral RAS (n = 6), ARAS (n = 5), or sham (n = 6). Stiffness of the cortex and the medulla was determined through 3-dimensional MRE, and renal perfusion and function were determined using multidetector computed tomography. Kidney fibrosis was subsequently assessed ex vivo using the Masson trichrome staining.
  
  
  RESULTS
  Renal stenotic cortex and medulla were significantly more fibrotic in RAS and ARAS compared with healthy kidney. However, MRE detected increased stiffness in RAS compared with the healthy kidney (12.7 ± 0.41 kPa vs 10.7 ± 0.18 kPa; P = 0.004) only in the medulla, which was further increased in ARAS (16.6 ± 1.3 kPa; P = 0.017 vs RAS). Magnetic resonance elastography-derived medullary, but not cortical, stiffness significantly correlated with histological degree of fibrosis, although cortical and medullary fibroses were correlated. Renal blood flow and function were similarly decreased in RAS and ARAS compared with the healthy kidney.
  
  
  CONCLUSIONS
  Noninvasive 3-dimensional MRE detects increased renal medullary stiffness in RAS and ARAS in vivo, which correlates with its fibrosis ex vivo and may also reflect cortical fibrosis. Hence, MRE-derived medullary stiffness can be potentially useful in detecting renal fibrosis and track disease progression.
authors.affiliation: Division of Nephrology and Hypertension, Mayo Clinic, Rochester, MN, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Korsmo
authors.forename: Behzad
authors.initials: B
authors.lastname: Ebrahimi
authors.forename: Alfonso
authors.initials: A
authors.lastname: Eirin
authors.forename: John R
authors.initials: JR
authors.lastname: Woollard
authors.forename: James D
authors.initials: JD
authors.lastname: Krier
authors.forename: John A
authors.initials: JA
authors.lastname: Crane
authors.forename: Lizette
authors.initials: L
authors.lastname: Warner
authors.forename: Kevin
authors.initials: K
authors.lastname: Glaser
authors.forename: Roger
authors.initials: R
authors.lastname: Grimm
authors.forename: Richard L
authors.initials: RL
authors.lastname: Ehman
authors.forename: Lilach O
authors.initials: LO
authors.lastname: Lerman
mesh_terms: D000818:Animals; D054459:Elasticity Imaging Techniques; D005260:Female; D005355:Fibrosis / Q000209:etiology; D007668:Kidney / Q000098:blood supply* / Q000473:pathology*; D012078:Renal Artery Obstruction / Q000150:complications* / Q000000981:diagnostic imaging*; D013552:Swine