Apparent diffusion coefficient characteristics of various adrenal tumors.

PURPOSE Using pathologically proven tumors and 3 methods of apparent diffusion coefficient (ADC) measurement, we examined the potential of diffusion-weighted imaging (DWI) to differentiate adrenal tumors. METHODS We evaluated adrenal tumors of 52 patients who underwent magnetic resonance (MR) examination including DWI and adrenal resection or biopsy between July 2006 and August 2011. Tumors included 25 cortical adenomas, 14 pheochromocytomas, 6 adrenal metastases, and seven others. We defined the tumor's "solid" region as an enhancing area on contrast-enhanced MR or computed tomography (CT) and measured the ADC of the tumor's "entire" and "solid" regions within a region of interest (ROI) placed on an ADC map ("entire" and "solid" ADCs). We obtained a "minimum" ADC by placing an ROI in an area showing the lowest ADC within the "solid" region. We also calculated the ratio of "non-solid" area to "entire" tumor and compared the average "entire," "solid," and "minimum" ADCs and the ratio of "non-solid" area to "entire" tumor between benign and malignant groups. RESULTS The average "entire" ADC was significantly higher for the benign (1.35 ± 0.38 × 10(-3) mm2/s) than malignant group (1.01 ± 0.17 × 10(-3) mm2/s), and the average "solid" and "minimum" ADC and the ratio of "non-solid" area to "entire" tumor did not differ significantly between the benign and malignant groups. CONCLUSION The higher "entire" ADC value of the benign group, which might be obtained incidentally, can be considered dependent on the condition of necrosis, hemorrhage, and degeneration. ADC measurement of a tumor's "solid" region was not useful for differentiating pathologically proven adrenal tumors.