As far as we know, the present report represents the first report to distinguish adrenal ganglioneuromas from lipid-poor adenomas using dual-phase enhanced CT scan as described. With the increased use of abdominal CT-scans, incidental detection of adrenal tumour is becoming more often. It is vital to discriminate adrenal ganglioneuromas from adenomas, particularly in the presence of a lipid-poor adrenal tumour. This retrospective study focused on several CT quantifiable parameters obtained from the unenhanced and dual-phase enhanced CT for differentiation of adrenal ganglioneuromas from lipid-poor adenomas. Our results manifested that CT value (CTU, CTA, CTV, DEAP, DEPP), age, tumor diameter, shape, and calcification were significant differently between the adrenal ganglioneuromas and lipid-poor adenomas.
In our study, we found that ganglioneuromas had a higher CTU than lipid-poor adenomas (P < .001), but a large overlap occurred between these 2 entities. Lee, Miyake et al pointed out that the threshold of 15-25 HU on noncontrast CT was a cut off for discrimination between adenomas and nonadenomas[19, 20]. The CTU criterion yielded 100% specificity, but the sensitivity of 46.8% was not high to become a discriminator. For our enhanced CT parameters, the CTA and CTV of lipid-poor adenomas were significantly higher than that of the ganglioneuromas. (P < .001). The threshold value of 51.5 HU of CTA, and 53.5 HU of CTV, respectively yielded 67.6%, and 88.0% sensitivity and 100%, and 88.1 % specificity for discrimination between ganglioneuromas and lipid-poor adenomas. Results from prior reports indicate that the mean enhanced CT value of the lipid-poor adenomas ranged from 55 HU to 83 HU[4, 11, 21]. Besides, the accessory quantitative parameters such as DEAP and DEPP were also significantly different between lipid-poor adenomas and ganglioneuromas which were obtained from dual-phase enhanced CT. Previous reports have confirmed that absolute or relative percentage washout of contrast material obtained from delayed contrast-enhanced CT scans (5min, 10min, 15min, 30min) is a useful method for the differentiation of lipid-poor from adrenal nonadenomas which reached a relatively high sensitivity and specificity[4, 22]. However, the high diagnostic efficiency was at the expense of long time of CT scan which also means more radiation dose for patients. Hence, our results suggested that CT attenuation value from early contrast CT could achieve considerable diagnostic efficiency for the differentiation between adrenal ganglioneuromas from lipid-poor adenomas compared with delayed contrast CT, which had vital clinical application value.
Adrenal lipid-poor adenomas were 14 years older, ranging from 20 to 76 years (mean, 52.4 years), than adrenal ganglioneuromas that ranged from 14 to 74 years (mean, 38.1 years) (P < .001). A prior study addressed that the discovery rate of adrenal adenomas increases with age. Our results showed that the mean age of lipid-poor adenomas were older than 50 years which were similar to previous reports, whereas precedent case reports on adrenal ganglioneuromas viewed that they mostly occur in older children and young which were not consist with our findings [4, 21, 24]. However, our results showed that age did not have a high diagnostic effectiveness in distinguishing lipid-poor adenomas from adrenal ganglioneuromas with a sensitivity and specificity of 63.4% and 85.7%, respectively, when the cut-off was set at 50.5 years old. Consequently, our analysis suggested that age may not be a useful discriminatory factor for distinguishing adrenal ganglioneuromas from adrenal lipid-poor adenomas.
The mean size of adrenal ganglioneuromas was 14 mm larger than lipid-poor adenomas (P < 0.05). Nevertheless, prior studies have reported overlap in size between adenomas and nonadenomas, which was also noticeable in this study[22, 25, 26]. The size criterion yielded 93.1% specificity, but the sensitivity of 45.2% was not high to be acknowledged as a discriminator.
Our results showed that most ganglioneuromas (88.1% [37 of 42]) were of oval or irregular shape, but lipid-poor adenomas (85.2% [184 of 216]) were more likely to have a round or oval shape (P < 0.05). In general, round, oval shapes are considered as a feature of benign tumor, while the irregular contour is associated with malignant lesions. Although the difference of shape between ganglioneuromas and adenomas is significant, it is not infallible as criterion in discriminating between ganglioneuromas and adenomas due to the fact that there is considerable overlap in shape. In our study, both cystic degeneration and hemorrhage were not likely to occur in ganglioneuromas and adenomas. It has been reported that cystic degeneration and hemorrhage typically occurs in adenomas when the size was larger than 4 cm.
The described calcification discovery rate ranged from 30 to 60% in ganglioneuromas, whereas only small cases have reported the presence of calcifications in adenomas[29–31]. In our study, the detection rate of calcification was 23.8% (10 of 42 ) in ganglioneuromas, compared with 6.0% (13 of 216) for lipid-poor adenomas (P < 0.05). Hence, we speculated that the presence of calcifications was more conducive to the diagnosis of ganglioneuromas.
Our study had several limitations. First, the number of ganglioneuromas was relatively smaller than that of lipid-poor adenomas due to its rarity. Second, our study had the connatural disadvantages of retrospective analysis, such as detection and selection biases. Besides, our data were obtained by using different devices. However, we insist that our data exploited beneficial information related to ganglioneuromas and lipid-poor adenomas. Finally, we did not compare absolute percentage washout ratio (APW) and relative percentage washout ratio (RPW) between these two groups whose diagnostic values have been confirmed in the discrimination of adenomas versus nonadenomas.
In conclusion, enhanced CT of the abdomen is a suitable approach for distinguishing ganglioneuromas from lipid-poor adenomas.