Minal C. Jagtiani MBBS, MD, Presenter: Nothing to Disclose

Giles Walter Boland MD, Abstract Co-Author: Principal, RCG HealthCare Consulting

Michael Austin Blake MBBCh, Abstract Co-Author: Nothing to Disclose

Elkan F. Halpern PhD, Abstract Co-Author: Research Consultant, Hologic, Inc

Peter F. Hahn MD, PhD, Abstract Co-Author: Nothing to Disclose

To study the inter- and intra- observer variation between two experienced adrenal imagers for their ability to differentiate lipid rich from lipid poor adrenal lesions on non- contrast CT.

All consecutive adrenal protocol studies (non-contrast and washouts) from November 2007 through March 2008 were analyzed. Thickening of the adrenal gland and myelolipomas were excluded for purposes of this study. Two adrenal imagers (R1 and R2 - with a combined experience of 29 years in adrenal imaging) independently assessed adrenal nodules for size and attenuation on the non- contrast images. For each reader, a region of interest was drawn over each nodule, covering two- thirds of the lesion and excluded regions of marked heterogeneity or calcification. Hounsfield (HU) value and standard deviation (SD) were recorded twice for each lesion, by each reader. Inter and intra-observer variability for measured length and average HU and SD were analyzed by the Bland- Altman analysis and t-test.

Ninety four patients (F: M 62: 31; age range 26-90; mean age 58± 12) and 101 discrete nodules (L: R 68: 33, mean size 2.08± 0.98, range 0.95- 5.65 cm) were analyzed. No inter-observer variability was observed for length (p= 0.01). Average length of lesions measured by R1 was 2.02± 1.08 cm, as compared to R2 which was 2.14± 0.93 cm. Range of measurements by R1 was 0.7 to 6.2 cm, while the range for R2 was 1 to 5.1 cm. There was no significant intra-observer difference for ROI measurements in Reader 1 (p= 0.7) or Reader 2 (p= 0.4). However, the ROI inter-observer variability was significantly different (p= 0.002). Range and mean HU for R1 and R2 were -21- 47 HU, 13.3± 14.5 and -22.5 - 43 HU, 14.6± 14.4 respectively. Average difference between the mean of the two readings (R1 and R2) is 0.67 HU ± 2.19. Of 101 lesions, R1 identified 43 lesions as benign (<10HU), while R2 identified 38 benign according to the same criteria. Conversely R2 identified 5 additional lesions as benign, which were deemed indeterminate by R1.

Significant inter-observer variability amongst experienced adrenal imagers exists when attempting to characterize adrenal lesions as lipid rich versus lipid poor.

Significant inter-observer differences, even for experienced imagers, undermines the ability of the test to differentiate lipid rich from lipid poor lesion.

Jagtiani, M, Boland, G, Blake, M, Halpern, E, Hahn, P, Characterization of Adrenal Lesions on Non-contrast CT: Inter and Intra- Observer Variation Differentiating Lipid Rich from Lipid Poor Lesions.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013070.html