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

Shaheed W Hakim; Nicola Schieda; Taryn Hodgdon; Matthew D F McInnes; Marc Dilauro; Trevor A Flood

doi:10.1007/s00330-015-3851-8

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

Eur Radiol. 2016 Feb;26(2):592-600. doi: 10.1007/s00330-015-3851-8. Epub 2015 Jun 3.

Authors

Shaheed W Hakim¹, Nicola Schieda², Taryn Hodgdon³, Matthew D F McInnes⁴, Marc Dilauro⁵, Trevor A Flood⁶

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. shakim@toh.on.ca.
² Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. nschieda@toh.on.ca.
³ Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. thodgdon@toh.on.ca.
⁴ Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. mmcinnes@toh.on.ca.
⁵ Department of Medical Imaging, The Ottawa Hospital, University of Ottawa, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. mdilauro@toh.on.ca.
⁶ 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.

PMID: 26032880
DOI: 10.1007/s00330-015-3851-8

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.

Keywords: Angiomyolipoma; Computed tomography; Fat; Magnetic resonance imaging; Ultrasound.

MeSH terms

Adipose Tissue
Adult
Aged
Angiomyolipoma / diagnosis*
Angiomyolipoma / pathology
Diagnosis, Differential
Female
Humans
Kidney Cortex / diagnostic imaging
Kidney Cortex / pathology
Kidney Neoplasms / diagnosis*
Kidney Neoplasms / pathology
Magnetic Resonance Imaging / methods*
Male
Middle Aged
Retrospective Studies
Tomography, X-Ray Computed / methods*
Ultrasonography