C. C. Taylor1, G. A. Rubio1, J. D. Egusquiza2, M. LoPinto1, J. I. Lew1 1University Of Miami,Division Of Endocrine Surgery, DeWitt Daughtry Family Department Of Surgery,Miami, FL, USA 2University Of Miami,Department Of Radiology,Miami, FL, USA
Introduction: Many recent studies suggest unenhanced CT attenuation values expressed in Hounsfield units (HU) are superior for differentiating between benign and malignant adrenal tumors. Surgical removal is warranted when the risk of malignancy is significant (i.e. adrenal tumor >4cm), or if the tumor is hyperfunctional biochemically. With recent enthusiasm for its use to differentiate between benign and malignant adrenal tumors, the purpose of this study was to determine if HU are more effective than tumor size by unenhanced CT in predicting adrenal malignancy.
Methods: A retrospective review of prospectively collected data of 40 patients who underwent adrenalectomies with reviewable unenhanced transverse CT scans at a single institution was performed. Based on final pathology, 32 patients had benign adrenal tumors and 8 had malignant tumors. CT densities were obtained in HU by placement of a region of interest (ROI) over the adrenal gland, avoiding any necrotic or hemorrhagic areas. Adrenal tumor size was determined using the maximum diameter on transverse CT views. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy at 2, 3, 4, 5, and 6 cm; and at 10, 20, 30, and 40 HU were also compared. Size and HU on CT were compared for benign and malignant adrenal tumors using unpaired T-tests.
Results: Of 40 patients studied, those with benign adrenal tumors had statistically (p<0.001) smaller diameters (3.6cm +/- 1.5) than malignant tumors (7.7cm +/- 4.4) [ROC curve 0.813, p<0.05]. The mean HU of benign tumors (26.5HU +/- 27) were not significantly different (p=0.28) compared to malignant tumors (37.8HU +/- 21) [ROC curve 0.659, p=0.169]. Unenhanced CT had a sensitivity of >85% and specificity of <55% for adrenal tumors measuring 2 to 4cm and a sensitivity of <63% and specificity >70% for tumors measuring 5 to 6cm. PPV, NPV, and accuracy for determining malignancy in adrenal tumors by size were: 24.2%, 100%, and 35.9% respectively at 2cm; 25.9%, 91.7%, and 46.2% at 3cm; 33.3%, 94.4%, and 61.5% at 4cm; 35.7%, 88%, and 69.2% at 5cm; and 80%, 88.2%, and 87.2% at 6cm. The sensitivity, specificity, PPV, NPV, and accuracy for determining malignancy in adrenal tumors by HU were: 100%, 16.1%, 23.5%, 100%, and 33.3% respectively at 10HU; 87.5%, 32.3%, 25%, 90.9%, and 43.6% at 20HU; 62.5%, 54.8%, 26.3%, 85%, and 56.4% at 30HU; and 50%, 83.9%, 44.4%, 86.7%, and 76.9% at 40HU.
Conclusion: This study suggests adrenal tumor size remains a better predictor for adrenal malignancy than HU on unenhanced CT. At 4cm, tumor size has a better sensitivity and specificity for predicting adrenal malignancy than HU. Furthermore, at 2cm or less, size is a more reliable predictor of adrenal benignity than HU. While use of HU has gained popularity, surgeons should remain confident in using tumor size as a criterion for those patients who require adrenalectomies.