Value of the CT "capsular sign" as a potential indicator of acute adrenal ischemia

Acute adrenal ischemia represents a rare cause of adrenal insufficiency which should be promptly diagnosed in order to preserve adrenal vitality and function. Our study aims to retrospectively evaluate the diagnostic accuracy of the CT capsular sign as an indicator of adrenal ischemia and its association with vascular involvement. Between January 2013 and January 2014, 69 consecutive patients (47 men, 22 women; mean age 46; range 22-67) with suspected adrenal insufficiency based on clinical and biochemical data underwent 320-row CT examination in our Emergency Department. Written informed consent was obtained for the CT examinations, and the institutional review board approval was obtained for our retrospective study. CT multi-planar images were retrospectively and independently analyzed by two radiologists searching for the patency of adrenal vessels, enlarged adrenals, the presence of the "capsular sign" represented by a peripheral subtle hyperdense line around a hypodense enlarged adrenal, and the presence of any periadrenal inflammatory changes. All CT findings were then compared with the surgical findings (n = 5), follow-up examinations (n = 20), or autopsy (n = 4). Sensitivity, specificity, diagnostic accuracy (DA), positive predictive value (PPV), and negative predictive value (NPV) were calculated for the "capsular sign" and were further evaluated by ROC analysis. Acute adrenal ischemia occurred in 29/69 patients (42 %), unilateral in 20, and bilateral in 9. Forty of sixty-nine patients (58 %) had no evidence of adrenal disease on CT. Thrombosis of the main adrenal vein was found in 20/29 (69 %) and non-venous ischemia in 9/29 (31 %). The capsular sign was found in 24/29 patients (83 %). Sensitivity, specificity, DA, PPV, and NPV values of 83, 100, 93, 100, and 89 %, respectively, were obtained. The capsular sign represents a CT indicator of acute adrenal ischemia, with a specificity of 100 % and leading to a prompt diagnosis in the early phase of the disease.