Objective: To retrospectively evaluate the usefulness of the apparent diffusion coefficients (ADCs) and dynamic contrast-enhanced magnetic resonance (MR) imaging for differentiation of malignant from benign pheochromocytomas at 3.0-T MR.
Methods: The Institutional Review Board approved this retrospective study, and informed consent was waived. Forty patients with pheochromocytomas underwent diffusion-weighted (DW) MR imaging in addition to T1- and T2-weighted sequences, chemical shift imaging techniques, and dynamic contrast-enhanced MR imaging at 3.0-T MR imaging system. In each patient, precontrast single-shot spin-echo echo-planar DW imaging was performed with b values of 0 and 800 seconds/mm2. In each patient, 3-dimensional fat-saturated T1-weighted dynamic contrast-enhanced MR imaging was performed at baseline (precontrast), during the arterial phase, and 1, 2, 3, and 5 minutes after contrast injection. Diagnosis was based on pathologic findings in surgical specimens. Independent samples t test was used to compare ADCs of benign and malignant pheochromocytomas. Receiver operating characteristic curve analysis was used to test the ability of ADCs in differentiating malignant from benign pheochromocytomas. Differences in dynamic contrast-enhanced patterns between malignant and benign pheochromocytomas were analyzed.
Results: Pathologic diagnoses revealed that 29 pheochromocytomas (three from both adrenal glands of the same patient) were benign and 13 were malignant. With b values of 0 and 800 seconds/mm2, mean ± SD ADC of malignant pheochromocytomas ([1.175 ± 0.132] × 10−3 mm2/s) was larger than that of benign ones ([0.918 ± 0.124] × 10−3 mm2/s), and the difference was significant (P < 0.001). Apparent diffusion coefficients obtained with b values of 0 and 800 seconds/mm2 were effective for distinguishing malignant from benign pheochromocytomas (area under the receiver operating characteristic curve, 0.906): A threshold value of 1.016 × 10−3 mm2/s permitted distinction with high sensitivity (93.3%) and specificity (77.8%). In dynamic contrast-enhanced MR imaging, malignant pheochromocytomas got peak signal intensity earlier (at arterial phase) than benign ones (at 1 minute after contrast injection).
Conclusion: In our limited study, ADCs in DW imaging with b values of 0 and 800 seconds/mm2 and dynamic contrast-enhanced pattern of malignant pheochromocytomas were significantly different from that of benign ones, suggesting that DW imaging and dynamic contrast-enhanced MR imaging may be useful in preoperative characterization and prognosis of pheochromocytomas, especially for those without obvious metastasis and vascular invasion.