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Angiomyolipoma (AML) without visible fat: Ultrasound, CT and MR imaging features with pathological correlation

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Abstract

Objective

To compare imaging findings with histopathology in AML without visible fat (AMLwvf).

Material and 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.

Key Points

• 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

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Acknowledgments

The scientific guarantor of this publication is Nicola Schieda, MD FRCP(C). The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article. The authors state that this work has not received any funding. One of the authors has significant statistical expertise. Institutional review board approval was obtained. Written informed consent was waived by the institutional review board. Methodology: retrospective, cross-sectional study, performed at one institution.

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Authors and Affiliations

  1. Department of Anatomical Pathology, The Ottawa Hospital, University of Ottawa, 501 Smyth Road, 4 floor CCW, Room 4278, Ottawa, Ontario, Canada, K1Y 4E9

    Shaheed W. Hakim & Trevor A. Flood

  2. Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9

    Nicola Schieda, Taryn Hodgdon, Matthew D. F. McInnes & Marc Dilauro

Authors
  1. Shaheed W. Hakim
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  2. Nicola Schieda
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  3. Taryn Hodgdon
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  4. Matthew D. F. McInnes
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  5. Marc Dilauro
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  6. Trevor A. Flood
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Corresponding author

Correspondence to Nicola Schieda.

Appendix

Appendix

Table 2 Pulse sequence parameters for dual-echo T1-weighted (in-phase and opposed-phase) GRE and T2-weighted FSE at 1.5 and 3 Teslaa
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Hakim, S.W., Schieda, N., Hodgdon, T. et al. Angiomyolipoma (AML) without visible fat: Ultrasound, CT and MR imaging features with pathological correlation. Eur Radiol 26, 592–600 (2016). https://doi.org/10.1007/s00330-015-3851-8

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  • DOI: https://doi.org/10.1007/s00330-015-3851-8

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