Ultrasonography of the Adrenal Gland

With appropriate techniques and using liver, spleen or kidney as an acoustic window, normal adrenal gland and adrenal lesions can be delineated by ultrasonography. The right adrenal gland is usually evaluated by transverse oblique scans and coronal scans, respectively, through the anterior and middle axillary line, while the left adrenal gland is investigated by an oblique coronal scan mainly through the posterior axillary line. For adrenal lesions, ultrasonography has a sensitivity of 74–97%, a specificity of 61–96%, and an accuracy of 70–97%. The diagnostic accuracy depends on the scanning technique and expertise of the operator, the body status of the patient, the size and functional status of the lesion, and the ultrasonographic quality. Small adrenal nodules, ileus, obesity, fatty liver, and large body status account for most of the reasons for decreased accuracy. Small adrenal nodules less than 3 cm in diameter mainly comprise functioning cortical adenomas, nonfunctioning cortical adenomas, nodular hyperplasia, and metastases. Most small adrenal masses are homogeneous and hypoechoic, and the echo patterns are nonspecific. Large adrenal masses greater than 3 cm in diameter mainly include primary adrenocortical carcinoma, lymphoma, metastasis, lymphoma, and pheochromocytoma. The echogenicity of a large adrenal mass may be hyperechoic and heterogeneous because of the higher incidence of necrosis and hemorrhage. Other uncommon adrenal masses are myelolipoma, hematoma, granulomatous lesions, hemangioma, and adrenal cysts of various origins. The differential diagnoses of a hyperechoic adrenal mass include neuroblastoma, myelolipoma, and tumor with central necrosis or heterogeneity. Calcification is encountered in both benign and malignant processes. It is sometimes difficult to differentiate benign adrenal masses from malignant lesions. Dynamic computed tomography, magnetic resonance imaging, and positron emission tomography play critical complementary roles in such an instance.