RESUMEN
The purpose of this study is to illustrate the role of US, CT and MRI in the characterization of adrenal metastases in patients with known primary cancer. Thirty metastatic adrenal masses and 10 adenomas were prospectively identified in 35 oncologic patients on non contrast and contrast enhanced CT scans of the chest and abdomen. All patients were studies with US, CT as well as chemical shift MRI [1.5 T]. Using CT, regions of interest were obtained at non enhanced, dynamic [60 seconds post contrast enhancement], and delayed [10 minutes post contrast enhanced] 3-8 mm thickness CT scans of the adrenal glands. These measurements were used to calculate a relative percentage contrast wash out as follows: 1-HU on delayed images/ HU on dynamic images x 100%. A relative percentage wash out threshold of 50% was applied with calculation of sensitivity and specificity of the protocol. Also the attenuation characteristics, size, shape and relation to nearby structures were determined on CT images. On MRI, the adrenal mass / splenic ratio [ASR] was calculated applying the chemical shift MRI protocol using 2.3 msec [out of phase images] and 4.6 msec [in phase images] echotime. The percentage of signal remaining in the out of phase images relative to the in phase images was determined. Diagnoses were confirmed by fine needle aspiration cytology, imaging findings and follow up findings. The study group included 35 patients with adrenal masses; 25 had 30 adrenal metastases and 10 patients had 10 adrenal adenomas. The malignant metastatic group included 20 men and 5 women. The mean age of 65 years. The non malignant group included 10 patients with adrenal adenomas, 8 women and 2 men, with mean age of 52 years. The primary malignant lesions were bronchogenic carcinoma in 14 patients, hepato-cellular carcinoma, renal cell carcinoma, infiltrating breast duct carcinoma, in 2 patients for each, colorectal, urinary bladder, uterine and prostatic carcinoma in one patient for each as well as one patient with pleural mesothelioma. US was performed as part of the routine diagnostic work up of patients. It could detect 23/30 [77%] adrenal metastases and 5/10 [50%] adrenal adenomas. Analysis of the CT images showed mean size of metastatic lesions of 4 cm [rang 3.3-12 cm], irregular shape in 25/30 [83%] lesion and heterogeneous attenuation in 26/30 [87%] lesion. The mean size of adrenal adenomas was 2.2 cm [range 1-3.2 cm], all were regular in shape and 90% shows homogeneous attenuation pattern. The mean CT attenuation values of the 30 metastatic lesions was 32 +/- 7.2HU. Only one lesion showed attenuation <18 HU. Adrenal adenomas shows mean attenuation values of 6 +/- 9.2 HU [range -20 to 19HU]. Only one adenoma showed attenuation >18 HU. The sensitivity: specificity ratio for the diagnosis of adrenal metastasis applying the CT attenuation characteristics was 97%: 90% at a threshold value of 18HU. Twenty nine of 30 [97%] metastatic lesions were correctly diagnosed as malignant with relative wash out threshold of 50% on delayed scans. All showed <50% contrast wash out. 90% adenomas shows contrast wash out of >50% at delayed post contrast scans. Therefore, the sensitivity and specificity of the protocol were 97% and 90% respectively. The analysis of the MR images revealed that signal intensity was not useful to reliable characterization of the adrenal metastatic lesions. Applying chemical shift imaging, 29/30 [97%] adrenal masses showed no significant signal loss in out of phase images. On the other hand, all adenomas [100%] showed marked signal loss in the out of phase images. The sensitivity and specificity of the protocol was 97% and 100% in differentiation of benign from metastatic adrenal masses. CSI was proved to be the most sensitive technique for differentiating adrenal adenoma from metastases. When CT examinations are equivocal, CSI would be the next imaging study of choice for characterization of adrenal masses