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Mediastinal tumours are frequently asymptomatic and first noted on routine chest radiograph. In most cases, evaluation should proceed to spiral computed tomography (sCT) of the chest with iodinated contrast material. The specific location and appearance of tumours on sCT is instrumental in planning further diagnostic and treatment strategies. Primary tumours in the anterior mediastinum account for half of all mediastinal masses. They comprise various benign and malignant neoplasms, but a wide variety of nonneoplastic lesions (developmental, inflammatory) can present as a localised mass in this compartment. The most common primary anterior mediastinal tumours are thymoma, teratoma and lymphoma; all other lesions are rare. Nonneoplastic conditions include thymic cysts, lymphangioma and intrathoracic goitre. Understanding the pathology, clinical presentation, imaging and diagnosis of the major tumour types is instrumental in the safe and efficient work-up of a mediastinal mass. Patients with primary mediastinal masses and cysts will usually undergo surgical resection; radiological and clinical features should prompt limited biopsy specimens followed by oncologic consultation, and chemotherapy or radiotherapy when appropriate. The objective of this review was to examine the role of diagnostic imaging in the management of masses of the anterior mediastinum.

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Objectives: To evaluate the usefulness of diffusion-weighted magnetic resonance for distinguishing thymomas according to WHO and Masaoka-Koga classifications and in predicting disease-free survival (DFS) by using the apparent diffusion coefficient (ADC). Methods:Forty-one patients were grouped based on WHO (low-risk vs. high-risk) and MasaokaKoga (early vs. advanced) classifications. For prognosis, seven patients with recurrence at followup were grouped separately from healthy subjects. Differences on ADC levels between groups were tested using Student-t testing. Logistic regression models and areas under the ROC curve (AUROC) were estimated. Results:Mean ADC values were different between groups of WHO (low-risk=1.58±0.20×10-3mm2/sec; high-risk=1.21±0.23×10-3mm2/sec; p<0.0001) and Masaoka-Koga (early=1.43±0.26×10-3mm2/sec; advanced=1.31±0.31×10-3mm2/sec; p=0.016) classifications.Mean ADC of type-B3 (1.05±0.17×10-3mm2/sec) was lower than type-B2 (1.32±0.20×10-3mm2/sec; p=0.023). AUROC in discriminating groups was 0.864 for WHO classification (cutpoint=1.309×10-3mm2/sec; accuracy=78.1 %) and 0.730 for Masaoka-Koga classification (cut-point=1.243×10-3mm2/sec; accuracy=73.2 %). Logistic regression models and two-way ANOVA were significant for WHOclassification (odds ratio[OR]=0.93, p=0.007; p<0.001), but not for Masaoka-Koga classification (OR=0.98, p=0.31; p=0.38). ADC levels were significantly associated with DFS recurrence rate being higher for patients with ADC≤1.299× 10-3mm2/sec (p=0.001; AUROC, 0.834; accuracy=78.0 %).Conclusions: ADC helps to differentiate high-risk from lowrisk thymomas and discriminates the more aggressive type-B3. Primary tumour ADC is a prognostic indicator of recurrence. Key Points• DW-MRI is useful in characterizing thymomas and in predicting disease-free survival.• ADC can differentiate low-risk from high-risk thymomas based on different histological composition • The cutoff-ADC-value of 1.309×10-3mm2/sec is proposed as optimal cut-point for this differentiation • The ADC ability in predicting Masaoka-Koga stage is uncertain and needs further validations• ADC has prognostic value on disease-free survival and helps in stratification of risk