Role of diffusion-weighted imaging in the differential diagnosis of benign and malignant lesions of the chest-mediastinum.

Purpose: We retrospectively evaluated the role of diffusion-weighted imaging (DWI) with fat and background signal suppression in the differential diagnosis of benign and malignant lesions of the chest-mediastinum by calculating the mean apparent diffusion coefficient (ADC) values. Materials and methods: Thirty-four patients with lung nodules/mediastinal masses underwent magnetic resonance (MR) imaging of the chest with conventional and DWI sequences. All patients had been previously studied with computed tomography (CT). After magnetic resonance (MR) imaging the patients underwent transthoracic CT-guided biopsy or mediastinoscopy. After the histopathological diagnosis had been obtained, the lesions were retrospectively divided into five groups: adenocarcinomas (n=16), squamous cell carcinomas (n=12), chronic pneumonias (n=2), malignant mediastinal tumours (n=2) and typical carcinoids (n=2). We compared ADC values in the different lesion groups using the Mann-Whitney U test. Results: There were statistically significant differences (p<0.05) between ADC values of benign and malignant lesions. Using an ADC value of 1.25×10⁻³ mm²/s as a threshold, we were able to differentiate malignant from benign lesions with 91% diagnostic accuracy, 90% sensitivity, 100% specificity, 100% positive predictive value and 57% negative predictive value. Conclusions: Short-tau inversion-recovery echo-planar imaging (STIR-EPI) sequences applied to the chest-mediastinum provided potentially useful images for the differential diagnosis of benign and malignant lesions.