title: Angiomyolipoma (AML) without visible fat: Ultrasound, CT and MR imaging features with pathological correlation.
abstract: OBJECTIVE
  To compare imaging findings with histopathology in AML without visible fat (AMLwvf).
  
  
  METHODS
  With IRB approval, we identified 18 AMLwvf that underwent CT between 2002-2014. A radiologist measured NECT-attenuation, corticomedullary (CM) and nephrographic (NG) enhancement, echogenicity relative to renal cortex (RC) (N = 5), T2W (T2AML/T2RC) signal-intensity (SI), and chemical-shift SI ([SIIN-PHASE - SIOPPOSED-PHASE]/SIIN-PHASE) indices (N = 6). A pathologist re-evaluated 15/18 AMLwvf for 1) < or > 25% adipocytes/high-power-field (HPF), 2) "many or few" blood vessels. Comparisons were performed using chi-square and independent t-tests.
  
  
  RESULTS
  73.3%(11/15) of AMLwvf had <25% adipocytes/HPF and 86.7%(13/15) had "many" blood vessels. NECT-attenuation was 41.8(±6.9) HU. 61.1 %(11/18) of AMLwvf were hyper-attenuating and 38.9%(7/18) iso-attenuating; attenuation was associated with %-adipocytes/HPF, (p = 0.01). CM/NG enhancement were 63.3(±20.8)/51.7(±15.5) HU. 72.2%(13/18) of AMLwvf had wash-out enhancement, with no association with amount of blood vessels at pathology, (p = 0.68). No difference in echogenicity was noted by histology (p > 0.05). All AMLwvf were T2-hypointense (SI ratio = 0.61 [±0.1]). 2/6 AMLwvf showed SI drop on chemical-shift MRI; both were iso-attenuating and were associated with >25% adipocytes/HPF (p = 0.04).
  
  
  CONCLUSIONS
  AMLwvf are typically T2-hypointense and hyper-attenuating with wash-out enhancement due to abundant smooth muscle and vessels respectively. Iso-attenuating AMLwvf with microscopic fat on MRI contain more adipocytes/HPF.
  
  
  CONCLUSIONS
  • Five percent of AML do not demonstrate detectable fat on imaging • These AML are hyperattenuating and T2-hypointense due to abundant smooth muscle • These AML show washout enhancement without association to vessel count at histopathology • Iso-attenuating AML with microscopic fat on MRI show >25% adipocytes/HPF • The term "AML without visible fat" is proposed to reduce ambiguity.
authors.affiliation: Department of Anatomical Pathology, The Ottawa Hospital, University of Ottawa, 501 Smyth Road, 4 floor CCW, Room 4278, Ottawa, Ontario, Canada, K1Y 4E9. shakim@toh.on.ca.
authors.forename: Shaheed W
authors.initials: SW
authors.lastname: Hakim
authors.affiliation: Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. nschieda@toh.on.ca.
authors.forename: Nicola
authors.initials: N
authors.lastname: Schieda
authors.affiliation: Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. thodgdon@toh.on.ca.
authors.forename: Taryn
authors.initials: T
authors.lastname: Hodgdon
authors.affiliation: Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. mmcinnes@toh.on.ca.
authors.forename: Matthew D F
authors.initials: MD
authors.lastname: McInnes
authors.affiliation: Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. mdilauro@toh.on.ca.
authors.forename: Marc
authors.initials: M
authors.lastname: Dilauro
authors.affiliation: Department of Anatomical Pathology, The Ottawa Hospital, University of Ottawa, 501 Smyth Road, 4 floor CCW, Room 4278, Ottawa, Ontario, Canada, K1Y 4E9. tflood@toh.on.ca.
authors.forename: Trevor A
authors.initials: TA
authors.lastname: Flood
mesh_terms: D000273:Adipose Tissue; D000328:Adult; D000368:Aged; D018207:Angiomyolipoma / Q000175:diagnosis* / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007672:Kidney Cortex / Q000000981:diagnostic imaging / Q000473:pathology; D007680:Kidney Neoplasms / Q000175:diagnosis* / Q000473:pathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014463:Ultrasonography
keywords: Angiomyolipoma; Computed tomography; Fat; Magnetic resonance imaging; Ultrasound