Renal masses: quantitative analysis of enhancement with signal intensity measurements versus qualitative analysis of enhancement with image subtraction for diagnosing malignancy at MR imaging.
OBJECTIVE
To retrospectively compare quantitative and qualitative methods of assessing magnetic resonance (MR) imaging contrast enhancement as the basis for diagnosing renal malignancy.


METHODS
MR imaging was performed by using a gadolinium-enhanced breath-hold fat-suppressed three-dimensional T1-weighted gradient-echo sequence in 71 patients (48 men and 23 women; mean age, 62 years; age range, 26-87 years) with 93 renal lesions for which pathologic correlation was available. For quantitative measurements of enhancement, the relative increase in signal intensity values was measured by one investigator with manually defined regions of interest, and the threshold of an increase of 15% or greater was used to distinguish malignant from benign masses. For qualitative assessment, two investigators independently reviewed the subtracted images of all lesions and subjectively determined whether enhancement was present or absent. The sensitivity, specificity, and positive and negative predictive values for each method were calculated and compared. Mean (+/- standard deviation) and median values of relative enhancement were also calculated for benign and malignant lesions.


RESULTS
At pathologic analysis, 74 (80%) of the 93 lesions were malignant, and 19 (20%)-including seven oncocytomas-were benign. For diagnosing malignancy based on enhancement alone, sensitivity and specificity, respectively, were 95% (70 of 74 lesions) and 53% (10 of 19 lesions) at quantitative analysis and 99% (73 of 74 lesions) and 58% (11 of 19 lesions) at qualitative analysis. All seven oncocytomas were considered to be malignant with both methods. When the oncocytomas were excluded, specificities increased to 83% (10 of 12 lesions) and 92% (11 of 12 lesions) for the quantitative and qualitative evaluations, respectively. Three of the four malignant lesions incorrectly characterized as benign at quantitative assessment were hyperintense on unenhanced MR images; all were diagnosed correctly at qualitative evaluation.


CONCLUSIONS
Image subtraction enables accurate assessment of renal tumor enhancement, particularly in the setting of masses that are hyperintense on unenhanced MR images.
Hecht
Elizabeth M
EM
Department of Radiology, New York University Medical Center, 560 First Ave, Suite HW 202, New York, NY 10016, USA.
Israel
Gary M
GM
Krinsky
Glenn A
GA
Hahn
Winnie Y
WY
Kim
Danny C
DC
Belitskaya-Levy
Ilana
I
Lee
Vivian S
VS
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002292:Carcinoma, Renal Cell / Q000175:diagnosis*; D003287:Contrast Media / Q000008:administration & dosage; D003937:Diagnosis, Differential; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007089:Image Enhancement; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D007668:Kidney / Q000473:pathology; D007674:Kidney Diseases / Q000175:diagnosis; D007680:Kidney Neoplasms / Q000175:diagnosis*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009378:Neoplasms, Multiple Primary / Q000175:diagnosis; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013382:Subtraction Technique
D003287:Contrast Media; D019786:Gadolinium DTPA