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Homogeneous T1 Hyperintense Renal Lesions with Smooth Borders: Is Contrast-enhanced MR Imaging Needed?
Amir H Davarpanah1, Michael Spektor1, Mahan Mathur1
1From the Department of Radiology, Division of Abdominal Imaging of Massachusetts General Hospital, Boston, Mass (A.H.D.), and Yale-New Haven Hospital, 20 York St, New Haven, CT 06510 (M.S., M.M., G.M.I.).
Abstract:
Purpose To retrospectively determine if homogeneous high T1 signal intensity (SI) masses with smooth borders on unenhanced magnetic resonance (MR) images can be characterized as benign. Materials and Methods Institutional review board approval was obtained for this HIPAA-compliant retrospective study, with waiver of informed consent. MR images in 84 patients with hemorrhagic or proteinaceous cysts and 50 patients with renal cell carcinoma (RCC) were evaluated. Sixty-three cysts and 49 RCCs underwent unenhanced computed tomography (CT). SI ratio and CT attenuation were determined. Two radiologists evaluated lesions as follows: score 1, homogeneous with smooth borders; score 2, mildly heterogeneous with mildly lobulated borders; score 3, moderately heterogeneous and irregular borders; and score 4, markedly heterogeneous with markedly irregular borders. Statistical analysis was performed by using multivariable logistic regression, Welch t test, Z test, Fisher-exact test, Shapiro-Wilk test, and receiver operating characteristic curve analysis. A diagnostic criterion was formulated by using classification and regression tree analysis. Results SI ratio and attenuation of hemorrhagic or proteinaceous cysts were significantly higher than those of RCCs (SI ratio: cyst 2.4 ± 0.8, RCC 1.5 ± 0.3; attenuation: cyst 51.9 ± 21.5, RCC: 34.8 ± 10.0). Reader 1 scored morphology of 68 (81%) hemorrhagic or proteinaceous cysts as score 1 on MR images and as score 45 (71%) on CT scans. Reader 2 scored morphology of 59 (70%) hemorrhagic or proteinaceous cysts as score 1 on MR images and as score 43 (68%) on CT scans. Two-step classification tree suggested that homogeneous high T1 SI lesions with smooth borders and SI ratio of greater than 1.6 predict the lesion as benign cysts. Similar algorithm for CT suggested threshold of 51 HU. Increasing threshold to 2.5 for SI ratio and 66 for Hounsfield units resulted in 99.9% confidence for characterizing benign cysts. Conclusion The retrospective assessment shows that morphologic assessment and SI quantification on unenhanced T1-weighted MR images can be used to differentiate benign hemorrhagic or proteinaceous cysts from RCC, although prospective assessment will be needed to confirm these results. (©) RSNA, 2016.
Insights
Homogeneous high T1 signal intensity masses with smooth borders on unenhanced MRI can reliably identify benign cysts. This imaging characteristic, along with a specific signal intensity ratio, helps differentiate these cysts from renal cell carcinoma (RCC).
Area of Science:
- Radiology
- Medical Imaging
- Oncology
Background:
- Differentiating benign hemorrhagic or proteinaceous cysts from renal cell carcinoma (RCC) is crucial for appropriate patient management.
- Unenhanced magnetic resonance (MR) imaging characteristics, particularly signal intensity (SI) and lesion morphology, may aid in this differentiation.
Purpose of the Study:
- To retrospectively evaluate if homogeneous high T1 signal intensity (SI) masses with smooth borders on unenhanced MR images can be accurately characterized as benign.
Main Methods:
- Retrospective analysis of unenhanced MR and computed tomography (CT) images from 84 patients with cysts and 50 with RCC.
- Radiologists assessed lesion morphology using a 4-score system.
- SI ratio and CT attenuation values were quantified.
Main Results:
- Hemorrhagic/proteinaceous cysts demonstrated significantly higher SI ratios and CT attenuation compared to RCC.
- A classification tree analysis identified homogeneous high T1 SI lesions with smooth borders and an SI ratio > 1.6 as predictive of benign cysts.
- Increasing thresholds for SI ratio and CT attenuation provided higher confidence in characterizing benign cysts.
Conclusions:
- Morphologic assessment and SI quantification on unenhanced T1-weighted MR images can differentiate benign hemorrhagic/proteinaceous cysts from RCC.
- Further prospective studies are warranted to confirm these findings.
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