Mediastinal Anatomy

Mediastinal anatomy is complicated which is close to a number of important tissues and organs. Moreover, tissue biopsy is difficult. Hence, it is difficult to establish a diagnosis and differentiate benign from malignant lymph nodes. There are invasive and noninvasive methods for evaluation of enlarged mediastinal lymph nodes. Invasive methods contain mediastinoscopes, thoracoscopes, transbronchial needle aspiration (TBNA), endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) and endoscopic ultrasound-guided fine needle aspiration (EUS-FNA). Although these methods can obtain pathological results,they are harmful for patients. The traditionalnoninvasive methods include computed tomography (CT) and magnetic resonance imaging
SUVmaxis preferred over SUVavg as there is a variability of about 35% between observers when SUVavg is used and this reduces to 3% when SUVmax is used[6].The SUVmax cutoff value of 2.5 is used commonly to differentiate between benign and malignant lesions[7].Kumar's study about 35 cases of mediastinal lymphadenopathy diseases showed that appropriately increasing the cut off values can improve the specificity, while maintaining an acceptable sensitivity[8]. When 2.5 or 6.2 was used as the cutoff value, the sensitivity, specificity, positive predictive value(PPV), negative predictive value (NPV), and accuracy were 93%, 40%, 54%, 89%, 63% and 87%, 70%, 68%, 87%, 77%, respectively[8]. However it has been shown that there is a significant number of false positivity (due to inflammatory diseases) and false negativity (due to low-grade