Mediastinal lymph nodes: assessment with diffusion-weighted MR imaging.

Purpose: To prospectively determine whether the diffusion-weighted magnetic resonance imaging is useful to distinguish between malignant and benign mediastinal lymph nodes.

Materials And Methods: Thirty-five patients (14 women, 21 men; mean age 52 years) with 91 lymph nodes in the mediastinum detected by computed tomography underwent 1.5 Tesla (T) diffusion-weighted MR imaging before mediastinoscopy (n = 29) and mediastinotomy (n = 6). Diffusion-weighted MR images were acquired with a b factor of 50, and 400 s/mm(2) using single-shot echo-planar sequence.

Results: Of the 35 patients, 18 had diagnosis of malignant tumor. Of the 18 patients with tumor, 8 had nonsmall cell carcinoma, and 10 had small cell carcinoma. Ninety-one mediastinal lymph nodes were detected in the 35 untreated patients: 19 were pathologically diagnosed as metastatic lymph nodes, and 72 lymph nodes were diagnosed as nonmetastatic lymph nodes, including 50 sarcoidosis, 14 reactive lymphoid hyperplasia, and 8 necrotizing granulamatous lymphadenitis. The apparent diffusion coefficient (ADC) was significantly lower in metastatic lymph nodes (1.012 +/- 0.025 x 10(-3) mm(2)/s; P < 0.0005) than in benign lymph nodes (1.511 +/- 0.075 x 10(-3) mm(2)/s). On the ADC map, malignant nodes showed hyperintense (n = 2, 10.52%), hypointense (n = 14, 73.68%), and mixed intensity (n = 3; 15.78%), whereas benign nodes showed hyperintense (n = 57; 79.16%), hypointense (n = 3; 41.6%), isointense (n = 6; 8.33%), and mixed intensity (n = 6; 8.33%).

Conclusion: Diffusion-weighted MR with ADC value and signal intensity can be useful in differentiation of malignant and benign mediastinal lymph nodes.