الفهرس 
Chapter 1: Anatomy of MediastinumOnly 14 pages are availabe for public view
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Abstract
Mediastinal masses span a wide histopathological and radiological spectrum, primary thymic neoplasms, thyroid masses and lymphomas are the most common in adults. Conventional radiography has a limited role in assessment of mediastinal masses. CT provides better contrast resolution and depicts the exact site, size, shape, number, contour and tissue characterization of mediastinal masses.
PET/CT: It combines the functional information of PET with the benefit of detailed anatomic data from CT. However, it is expensive, relatively unavailable with the disadvantage of exposure to ionizing radiation and radioactive material. Magnetic Resonance Imaging advantages are lack of ionizing radiation, confirm cystic nature of mediastinal cystic masses, superior soft tissue contrast in assessment of mediastinal masses and chest wall invasion by a tumor.
Diffusion describes the microscopically visualized random motion of water molecules as they diffuse through extracellular space. regions of high mobility ’ rapid diffusion’ is dark signal, regions of low mobility ’ restricted diffusion’ is bright signal.
Diffusion differentiates of benign from malignant mediastinal masses. Malignant lesions have more tightly packed cells with a more compact architecture and, consequently, there is restricted diffusion of water molecules in malignant lesions showing lower ADC values as compared with benign lesions.
Diffusion differentiates of central mass from post obstructive collapse.in T1W1 the post-obstructive atelectasis often show higher signal intensities than the central tumour.in DWI the central bronchogenic carcinomas will show higher signal intensity and lower ADC values than benign obstructive atelectasis, according to differences in cellularity and grade of occupancy of the interstitium.
The mean ADC value in metastatic lymph nodes is less than that in nodes without metastases and similar to that in primary lesions, in which movement is limited due to high cellularity.
Diffusion MR imaging can be used for detection of distant metastasis e.g. bone metastasis, liver metastases and suprarenal metastasis.
DWI was tested for the differentiation between probably benign (transudative) effusions from probably malignant (exudative) ones. Malignant effusion will show higher signal intensity in DWI and lower ADC value.
Mediastinal-hilar lymphadenopathy has a wide spectrum of differential diagnosis. Lymphoma and sarcoidosis form a great part of the differential diagnosis as the malignant and benign counterparts.
The ADC of lymphoma is lower than that of sarcoidosis. In 2013, Gümüştaş et al., reported that the mean ADC for lymphoma was (1.13x10-3) mm2/s and for sarcoidosis was (2.065 x10-3) mm2/s.
Conclusion:-
DWI differentiates of malignant mediastinal tumors from benign lesions and this is essential for treatment planning as well as for prediction of prognosis.