The mediastinum is located between the two lungs and contains the heart, thymus, large vessels, trachea, main bronchi, esophagus, lymph nodes and some important nerves. In the mediastinum, bronchi, esophagus and thymus-related diseases, especially tumors are common. In addition, diseases that cause growth in lymph nodes like lymphoma, and metastatic tumors of the lymph nodes such as lung, head and neck tumors, are also quite common.

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The masses in the mediastinum can be biopsied in three ways: 1. Surgical biopsy (mediastinoscopy). 2. Bronchoscopic biopsy. 3. Percutaneous biopsy. In the surgical method, an incision is made in the lower part of the neck and a mediastinoscope is inserted into the mediastinum cavity and biopsies are taken. Surgical biopsy is an invasive procedure performed under general anesthesia and through an incision, and it may not be possible to take samples from some locations of the mediastinum. Bronchoscopic biopsy is an ideal biopsy technique for lesions adjacent to the trachea and main bronchi, but it is less accurate because it is made with a thin needle, but it is not usually possible to take a biopsy from tumors not adjacent to main bronchi.

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Although percutaneous biopsy is a very useful technique for mediastinal masses, it is applied only in a few centers, like lung biopsy. For mediastinal biopsy, under local anesthesia and CT guidance, a needle is advanced to the target mass and then a thinner trucut needle is passed through this needle (coaxial system) to obtain multiple pieces from the target mass. In order not to cause pneumothorax, the mediastinum can be extended and the lung tissue can be pushed aside by injecting fluid through the needle.  Mediastinal biopsy can be performed in several ways: 

 

1.Transsternal approach: The chest wall is crossed with a  needle from the sternum and multiple biopsies are taken from the target mass with a coaxial trucut needle. This approach is safe and effective for the thymus or lymph node masses behind the sternum.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

2. Parasternal approach: It is done by advancing the needle next to the edge of the sternum and not through the bone. It is commonly performed for masses located in the anterior mediastinum and around the aortic arch.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3. Paravertebral approach: The needle is advanced through the space between the lung and the edge of the spine, without passing the lung tissue, and when the target is reached, multiple biopsies are taken with the coaxial trucut needle. It is mostly used in the masses located in the posterior mediastinum (lymph nodes and the tumors of esophagus, trachea and main bronchi tumors).

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

4. Transpulmonary approach: In the transsternal, parasternal and paravertebral approaches, there is no risk of pneumothorax since the needle is not passed through the lung. However, in some cases, it is not possible to reach the target tumor with any of these approaches. In these cases, as a last resort, the needle is advanced through the lung into the target mass and trucut biopsies are taken with the coaxial system. In the transpulmonary approach, the risk of pneumothorax is higher than that of normal lung biopsy because the lung membrane (pleura) is punctured twice. Despite that, in experienced hands, this biopsy can be performed without a serious problem in the vast majority of cases.

 

Video information: "CT-guided lung and mediastinum biopsies"