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Updated: May 18, 2026
In Vivo, Percutaneous, Needle Based, Optical Coherence Tomography of Renal Masses
Published on: March 30, 2015
Angiomyolipoma with minimal fat: can it be differentiated from clear cell renal cell carcinoma by using standard MR
Nicole Hindman1, Long Ngo, Elizabeth M Genega
1Department of Radiology, New York University Langone Medical Center, New York, NY, USA.
Purpose:
To retrospectively assess whether magnetic resonance (MR) imaging with opposed-phase and in-phase gradient-echo (GRE) sequences and MR feature analysis can differentiate angiomyolipomas (AMLs) that contain minimal fat from clear cell renal cell carcinomas (RCCs), with particular emphasis on small (<3-cm) masses.
Materials And Methods:
Institutional review board approval and a waiver of informed consent were obtained for this HIPAA-compliant study. MR images from 108 pathologically proved renal masses (88 clear cell RCCs and 20 minimal fat AMLs from 64 men and 44 women) at two academic institutions were evaluated. The signal intensity (SI) of each renal mass and spleen on opposed-phase and in-phase GRE images was used to calculate an SI index and tumor-to-spleen SI ratio. Two radiologists who were blinded to the pathologic results independently assessed the subjective presence of intravoxel fat (ie, decreased SI on opposed-phase images compared with that on in-phase images), SI on T1-weighted and T2-weighted images, cystic degeneration, necrosis, hemorrhage, retroperitoneal collaterals, and renal vein thrombosis. Results were analyzed by using the Wilcoxon rank sum test, two-tailed Fisher exact test, and multivariate logistic regression analysis for all renal masses and for small masses. A P value of less than .05 was considered to indicate a statistically significant difference.
Results:
There were no differences between minimal fat AMLs and clear cell RCCs for the SI index (8.05%±14.46 vs 14.99%±19.9; P=.146) or tumor-to-spleen ratio (-8.96%±16.6 and -15.8%±22.4; P=.227) when all masses or small masses were analyzed. Diagnostic accuracy (area under receiver operating characteristic curve) for the SI index and tumor-to-spleen ratio was 0.59. Intratumoral necrosis and larger size were predictive of clear cell RCC (P<.001) for all lesions, whereas low SI (relative to renal parenchyma SI) on T2-weighted images, smaller size, and female sex correlated with minimal fat AML (P<.001) for all lesions.
Conclusion:
The diagnostic accuracy of opposed-phase and in-phase GRE MR imaging for the differentiation of minimal fat AML and clear cell RCC is poor. In this cohort, low SI on T2-weighted images relative to renal parenchyma and small size suggested minimal fat AML, whereas intratumoral necrosis and large size argued against this diagnosis.
Insights
Magnetic resonance (MR) imaging with opposed-phase and in-phase gradient-echo sequences has poor accuracy in differentiating minimal fat angiomyolipomas (AMLs) from clear cell renal cell carcinomas (RCCs). Small size and low T2 signal intensity suggest AML, while necrosis and larger size indicate RCC.
Area of Science:
- Radiology
- Oncology
- Medical Imaging
Background:
- Renal masses require accurate differentiation for appropriate clinical management.
- Minimal fat angiomyolipomas (AMLs) and clear cell renal cell carcinomas (RCCs) can present similar imaging characteristics, posing a diagnostic challenge.
- Distinguishing these entities, especially small renal masses (<3 cm), is crucial.
Purpose of the Study:
- To evaluate the efficacy of magnetic resonance (MR) imaging, specifically opposed-phase and in-phase gradient-echo (GRE) sequences, in differentiating minimal fat AMLs from clear cell RCCs.
- To assess the utility of MR feature analysis in characterizing small renal masses (<3 cm).
Main Methods:
- Retrospective analysis of MR images from 108 pathologically proven renal masses (20 minimal fat AMLs, 88 clear cell RCCs).
- Calculation of signal intensity (SI) index and tumor-to-spleen SI ratio using opposed-phase and in-phase GRE sequences.
- Independent assessment by two radiologists of subjective MR features including fat, T1/T2 SI, cystic degeneration, necrosis, hemorrhage, and vascular invasion.
Main Results:
- No significant difference in SI index or tumor-to-spleen ratio between minimal fat AMLs and clear cell RCCs (P > .05).
- Diagnostic accuracy for SI index and tumor-to-spleen ratio was low (AUC = 0.59).
- Intratumoral necrosis and larger size were predictive of clear cell RCC (P<.001), while low T2 SI, smaller size, and female sex were associated with minimal fat AML (P<.001).
Conclusions:
- Opposed-phase and in-phase GRE MR imaging demonstrate poor diagnostic accuracy for differentiating minimal fat AML from clear cell RCC.
- Small size and low T2-weighted signal intensity relative to renal parenchyma are suggestive of minimal fat AML.
- Intratumoral necrosis and larger size are indicative of clear cell RCC.
