Though biochemical testing is recommended for the workup of incidental adrenal nodules with reported accuracy of over 90% for diagnosis of pheochromocytoma[3, 8, 30], these tests may be falsely positive[9]. To differentiate the PHEOs from incidental adrenal nodules, especially the result of biochemical testing is positive, we investigate the magnetic resonance imaging characteristics. In our study, there is distinct significance in tumor size (LD: 39.83 ± 19.23 mm versus 24.19 ± 9.43 mm; p = 0.001) among PHEOs from non-PHEOs, although we didn't include it in the final logistic regression analysis. On one hand, pheochromocytomas demonstrated higher T2W and T2-spair signal intensity compared to adenoma, similar to what has been published previously[31]. Varghese et al were the first to assess adrenal lesions SI at T2-weighted MRI comparing pheochromocytomas and adenomas, showing that a majority of adenomas showed low T2-weighted signal[24]. As we all know that very high T2W signal intensity is a representative characteristic of pheochromocytoma; nevertheless, approximately 30% of pheochromocytomas are not bright on T2W[24]. On the other hand, T2-weighted SI ratio was also significantly higher in PHEOs adenomas compared with non-PHEOs, independent predictive factor for differentiating PHEOs. Moreover, for chemical shift and chemical shift ratio, significant differences obtained to distinct pheochromocytomas from adrenal nodules in our study. Our study is concordant with what has been proved previously[32]. Our study suggested that the values of ADC might add helpful information in differentiating pheochromocytomas from non-pheochromocytomas. Adenomas indicate with low ADC values on MRI which was attributed to lipid content and intensive packed cells[33, 34].
Our study specifically evaluated a common clinical problem, which is the management of an incidentally discovered adrenal nodule in a patient that shows the result of biochemical testing beyond the upper reference limit. The most efficient variable was selected to differentiate PHEOs from adrenal incidentalomas by logistic regression analysis, with the high sensitivity, specificity and accuracy. However, our present study has some limitations that need to be addressed in future studies. First, the number of samples included is limited, which might limit the capacity of the data analyses. It may be that inclusion criteria are quite strict, received MRI and biochemical testing must be present is positive。However, only patients with pathological diagnosis have been included in the investigation, which is also considered a strength. Second, it was a single-center retrospective study that may have been subject to selection bias, may limit broader applicability of our results; verification of our results in other institutions is necessary. Third, we didn't compare the effects of heterogeneity on them, although attempted to reduce impact by measuring methods. Moreover, three radiologists are blinded to the pathologic diagnosis reviewed all existing MRI images to reduce differences. However, we included more magnetic resonance parameters to study the characteristics of magnetic resonance imaging to differentiate pheochromocytomas among adrenal tumors more comprehensively compared to previous studies. Future research should include a great deal of samples to evaluate for potential improvements in accuracy by adding additional variables (including size and demographic variables) into logistic regression analysis.
In conclusion, our study demonstrates that the T2-weighted SI ratio, with highly sensitivity, specificity, and overall accuracy to differentiate adrenal pheochromocytomas from adrenal tumors. Pheochromocytoma is badly dangerous and needs to be treated with caution. Therefore, it is crucial to identify PHEOs accurately, when the outputs of biochemical testing exceed the upper limit of the reference value. These observations and propose thresholds are required to validate in the future multicenter studies, which could enable diagnosis in clinical practice.