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Characterization of adrenal masses with diffusion-weighted imaging

UROLOGICAL SURVEY

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Characterization of adrenal masses with diffusion-weighted imaging

Sandrasegaran K; Patel AA; Ramaswamy R; Samuel VP; Northcutt BG; Frank MS; Francis IR

Department of Radiology, Indiana University School of Medicine, Indianapolis, 46202, USA

AJR Am J Roentgenol. 2011; 197: 132-8

OBJECTIVE: The purpose of this article is to assess the role of diffusion-weighted MRI in characterizing adrenal masses.

MATERIALS AND METHODS: A retrospective review of the MRI database from August 2007 to July 2009 was performed.

The MRI examinations of 48 patients, with 49 lesions, were reviewed independently and blindly by two experienced abdominal radiologists who measured the signal intensities on in-phase and opposed-phase T1-weighted imaging and apparent diffusion coefficient (ADC). ADC measurements and quantitative parameters of chemical shift imaging (signal intensity index and adrenal-to-spleen ratio) were assessed separately and in combination. Lesions with indeterminate signal intensity index (< 16.5%) were considered benign if ADC was greater than or equal to 1.0 × 10(-3) mm(2)/s and malignant if ADC was less than 1.0 × 10(-3) mm(2)/s.

Stepwise logistic regression analysis and receiver operating characteristic curves analysis were performed.

RESULTS: There were 12 malignant and 37 benign lesions. On multivariate analysis, the only significant predictors of lesion status were signal intensity index from reviewer 2 (p = 0.05) and lesion size (p = 0.04); ADC values were not found to be useful. On receiver operating characteristic curve analysis, there was no significant difference in area under the curve for ADC, signal intensity index, adrenal-to-spleen ratio, or the combined signal intensity index and ADC assessment. For lesions that were indeterminate according to signal intensity index, ADC values greater than 1.50 × 10(-3) mm(2)/s were found only in benign lesions, and nine of 11 lesions with ADC less than 1.0 × 10(-3) mm(2)/s were malignant.

CONCLUSION: In general, ADC values are not useful in differentiating adrenal lesions. However, when ADC values are applied to lesions that are indeterminate on signal intensity index, they may help in differentiating a subset of benign and malignant lesions.

Editorial Comment

Adrenal incidentalomas are found in about 6% of patients submitted to abdominal computed tomography. Based on distinct radiologic criteria classified as morphologic (size, shape, rate of growing), histologic (lipid content of the mass on CT without contrast or on chemical-shift imaging on MRI without contrast) and physiologic (absolute washout of contrast on CT), the vast majority of adrenal incidentalomas are adequately characterized as a benign or malignant. Lipid rich adrenal adenoma loses signal intensity when protons from water and fat are on opposed-phase in comparison with imaging when these protons are inphase. Signal intensity index higher than 16.5% is usually found in benign adenomas. Indeterminate adrenal lesion represents a lesion with signal intensity index below 16.5%. In such situation, the authors showed that use of ADC values obtained with diffusion-weighted imaging (DWI) might be useful in differentiating benign from malignant adrenal lesions.

Although in our protocol for DWI of adrenal masses we use a different "b-value" (b-factor of 1000), we have found no utility of DWI even in this selected group of patients with indeterminate lesion on CSI. Actually we have seen two out of 13 adrenal adenomas showing the lowest ADC values. As pointed out by the authors, the different proportion of lipid-poor adenomas and fat-containing adrenal metastases may explain distinct results with DWI.

Dr. Adilson Prando

Head, Department of Radiology and

Diagnostic Imaging, Vera Cruz Hospital

Campinas, São Paulo, Brazil

E-mail: adilson.prando@gmail.com

Publication Dates

  • Publication in this collection
    16 Feb 2012
  • Date of issue
    Dec 2011
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