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Published online before print November 26, 2008, 10.1148/radiol.2502080302

(Radiology 2009;250:474.)

A more recent version of this article appeared on February 1, 2009
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© RSNA, 2008

Genitourinary Imaging

Distinguishing Adrenal Adenomas from Nonadenomas: Combined Use of Diagnostic Parameters of Unenhanced and Short 5-minute Dynamic Enhanced CT Protocol1

Takuro Kamiyama, MD, Yoshihiko Fukukura, MD, PhD, Tomohide Yoneyama, MD, Koji Takumi, MD, and Masayuki Nakajo, MD, PhD

1 From the Department of Radiology, Kagoshima University Graduate School of Medical and Dental Sciences, 8-35-1 Sakuragaoka, Kagoshima 890-8544, Japan. Received February 14, 2008; revision requested April 30; final revision received July 4; accepted July 23; final version accepted August 27. Address correspondence to T.K. (e-mail: takuro3{at}m2.kufm.kagoshima-u.ac.jp).

Purpose: To retrospectively examine the diagnostic values of individual parameters obtained from unenhanced and 35-second and 5-minute contrast material–enhanced (enhanced) computed tomography (CT) in distinguishing adenomas, particularly lipid-poor adenomas, from nonadenomas and to determine the best diagnostic method by using these parameters.

Materials and Methods: This retrospective study had institutional review board approval; the need for informed consent was waived. The study population consisted of 61 patients (20 men and 41 women; mean age, 58 years) with 68 adrenal masses (53 adenomas and 15 nonadenomas). In each patient, unenhanced CT was followed by 35-second and 5-minute enhanced CT. Adenomas were classified as 30 lipid-rich (≤10 HU) and 23 lipid-poor (>10 HU) adenomas by using unenhanced attenuation. The diagnostic parameters were tumor size, unenhanced attenuation, 35-second and 5-minute enhanced attenuation, wash-in and washout attenuation, percentage enhancement washout ratio (PEW), and relative PEW (RPEW). The sensitivity, specificity, and accuracy for diagnosing adenomas were calculated by using a threshold level of each parameter determined by the least sum of false-positive and false-negative cases and a combination of the threshold levels with 100% specificity.

Results: The best results were obtained by using a combination of the threshold levels with 100% (15 of 15) specificity (presence of at least one of the following criteria for diagnosing adenomas: unenhanced attenuation of ≤19 HU, 5-minute attenuation of ≤50 HU, PEW of ≥45%, and RPEW of ≥31%). Sensitivity was 94% (50 of 53) or 87% (20 of 23) and accuracy was 96% (65 of 68) or 92% (35 of 38) for diagnosing total adrenal adenomas or lipid-poor adenomas, respectively.

Conclusion: Combining the diagnostic parameters of the CT protocol can yield diagnostic results comparable to those with previously reported longer dynamic enhanced CT protocols.

© RSNA, 2008