MRI evaluation of small (<4cm) solid renal masses: multivariate modeling improves diagnostic accuracy for angiomyolipoma without visible fat compared to univariate analysis.
OBJECTIVE
To assess MRI for diagnosis of angiomyolipoma without visible fat (AMLwvf).


METHODS
With IRB approval, a retrospective study in consecutive patients with contrast-enhanced (CE)-MRI and <4 cm solid renal masses from 2002-2013 was performed. Ten AMLwvf were compared to 77 RCC; 33 clear cell (cc), 35 papillary (p), 9 chromophobe (ch). A blinded radiologist measured T2W signal-intensity ratio (SIR), chemical-shift (CS) SI-index and area under CE-MRI curve (CE-AUC). Regression modeling and ROC analysis was performed.


RESULTS
T2W-SIR was lower in AMLwvf (0.64 ± 0.12) compared to cc-RCC (1.37 ± 0.30, p < 0.001), ch-RCC (0.94 ± 0.19, p = 0.005) but not p-RCC (0.74 ± 0.17, p = 0.2). CS-SI index was higher in AMLwvf (16.1 ± 31.5 %) compared to p-RCC (-5.2 ± 26.1 %, p = 0.02) but not ch-RCC (3.0 ± 12.5 %, p = 0.1) or cc-RCC (7.7 ± 17.9 %,p = 0.1). CE-AUC was higher in AMLwvf (515.7 ± 144.7) compared to p-RCC (154.5 ± 92.8, p < 0.001) but not ch-RCC (341.5 ± 202.7, p = 0.07) or cc-RCC (520.9 ± 276.9, p = 0.95). Univariate ROC-AUC were: T2SIR = 0.86 (CI 0.77-0.96); CE-AUC = 0.76 (CI 0.65-0.87); CS-SI index = 0.66 (CI 0.4.3-0.85). Logistic regression models improved ROC-AUC, A) T2 SIR + CE-AUC = 0.97 (CI 0.93-1.0) and T2 SIR + CS-SI index = 0.92 (CI 0.84-0.99) compared to univariate analyses (p < 0.05). The optimal sensitivity/specificity of T2SIR + CE-AUC and T2SIR + CS-SI index were 100/88.8 % and 60/97.4 %.


CONCLUSIONS
MRI, using multi-variate modelling, is accurate for diagnosis of AMLwvf.


CONCLUSIONS
• AMLwvf are difficult to prospectively diagnose with imaging. • MRI findings associated with AMLwvf overlap with various RCC subtypes. • T2W-SI combined with chemical-shift SI-index is specific for AMLwvf but lacks sensitivity. • T2W-SI combined with AUC CE-MRI is sensitive and specific for AMLwvf. • Models incorporating two or more findings are more accurate than univariate analysis.
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9. nschieda@toh.on.ca.
Nicola
N
Schieda
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9.
Marc
M
Dilauro
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9.
Bardia
B
Moosavi
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9.
Taryn
T
Hodgdon
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9.
Gregory O
GO
Cron
Department of Medical Imaging, The Ottawa Hospital, 1053 Carling Avenue, Ottawa, Ontario, Canada, K1Y 4E9.
Matthew D F
MD
McInnes
Department of Anatomical Pathology, The Ottawa Hospital, The University of Ottawa, 501 Smyth Road, 4th floor CCW, Room 4278, Ottawa, Ontario, Canada, K1Y 4E9.
Trevor A
TA
Flood
D000273:Adipose Tissue / Q000000981:diagnostic imaging*; D000328:Adult; D000368:Aged; D018207:Angiomyolipoma / Q000000981:diagnostic imaging* / Q000473:pathology; D002292:Carcinoma, Renal Cell / Q000000981:diagnostic imaging* / Q000473:pathology; D003287:Contrast Media; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D007680:Kidney Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D016015:Logistic Models; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D012372:ROC Curve; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D047368:Tumor Burden
D003287:Contrast Media
Angiomyolipoma; Contrast enhanced; Magnetic resonance imaging; Minimal fat; T2 weighted imaging