Size Better Predicts Adrenal Malignancy compared to Hounsfield Units on Unenhanced CT​

Objective: Hounsfield units (HU) may better determine malignant adrenal tumors than size criterion of >4 cm by CT imaging. This study determines if HU are more effective than size criterion in predicting adrenal... [ view full abstract ]

Objective: Hounsfield units (HU) may better determine malignant adrenal tumors than size criterion of >4 cm by CT imaging. This study determines if HU are more effective than size criterion in predicting adrenal malignancy. 

 Methods: A retrospective review of 40 patients who underwent adrenalectomy with reviewable unenhanced CT scans at a single institution was performed. 32 patients had benign, and 8 had malignant adrenal tumors on final pathology. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and accuracy from 2 to 6 cm; and 10 to 40 HU were compared for benignity and malignancy using unpaired t-tests

 Results: Adrenal tumors 2 to 4 cm by CT had sensitivity of >85% and specificity of <55%, whereas tumors 5 to 6 cm had sensitivity <63% and specificity >70% for malignancy. PPV, NPV, and accuracy for malignancy by size: 24.2%, 100%, and 35.9% for 2cm; 25.9%, 91.7%, and 46.2% for 3cm; 33.3%, 94.4%, and 61.5% for 4cm; 35.7%, 88%, and 69.2% for 5cm; 80%, 88.2%, and 87.2% for 6cm. Sensitivity, specificity, PPV, NPV, and accuracy for malignant adrenal tumors by HU were: 100%, 16.1%, 23.5%, 100%, and 33.3% 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: Adrenal tumor size >4cm better predicts adrenal malignancy than HU on unenhanced CT. While use of HU has gained popularity, surgeons should remain confident using size for determining malignancy in adrenal tumors by CT imaging.