Background: Different paravertebral pathologies in posterior mediastinum may cause diagnostic difficulties. Usually, the symptoms are not specific, and the changes are found during routine investigations. In roentgenograms, they do not have specific features so more accurate imaging modality must be chosen to define whether it is benign or malignant. This can be made by using a CT or MRI scan. It is crucial to choose the right strategy for each pathology, as the aim of imaging may vary in different situations. The aim of our study was to evaluate and compare the features of pathological findings in the posterior mediastinum. Materials and methods: We performed the retrospective observational study at LUHS hospital Kauno Klinikos Radiology clinic. Medical health records and x-ray, CT and MRI radiologic view made between 2015 and 2019 were analyzed. Patients who underwent CT and MRI scanning repeatedly for clarification of diagnosis were investigated PET/CT or were operated for histological confirmation of diagnosis and who had pathologic findings in posterior mediastinum were selected. Results: The study consisted of 81 patients with verified posterior mediastinal masses. A variety of clinical diagnoses were confirmed, 70,4% (n = 57) of the masses were oesophagal tumours, and the remaining cases consisted of benign cysts and other cysts like lesions. Oesophagal tumours were most commonly located in the middle thoracic part of the oesophagus and presented itself as a circular wall thickening with a homogenous structure and a rare rate of local invasion of adjacent structures. There was a statistically significant difference between attenuation on CT scan before and after the administration of intravenous contrast medium (p<0,001). The majority of cystic masses 66,7% (n=16) presented with a well-defined circumscribed border on a conventional radiograph. CT images showed that 79,2% (n=19) masses were heterogeneous and had a various degree of contrast enhancement. In diffusion-weighted magnetic resonance imaging, ADC values was measured with an average of 1,860,99 * 10-3mm2/s. PET/CT showed hypermetabolism in 41,7% (n=10) of the masses and possibly benign, no metabolic changes in the remaining 58,3% (n=14). There was no statistically significant difference in mean attenuation measured on CT between metabolically active and inactive masses (p=0,546). There was a statistically significant difference in apparent diffusion coefficient between metabolically active and inactive masses (p=0,005). Conclusion: Conventional chest radiography can be helpful to define the anatomical location, borders and size of the masses. Multislice computed tomography can help to obtain information about densities and CE of the lesion. In different sequences of MRI masses have an isointense or hyperintense signal which provides additional information about the inner structure of lesion. Apparent diffusion coefficient (ADC) in MRI can be helpful distinguishing malignant from benign masses.
Keywords: computed tomography, magnetic resonance imaging, posterior mediastinum