Fritz J. Baumgartner
The mediastinum can generally be classified into three compartments—anterior, middle and posterior mediastinum (Fig. 18.1). The anterior mediastinum may be subcategorized into anterior and superior mediastinum. The superior mediastinum lies above a plane extending from the sternal angle of Louis to the level of T4. The mediastinum inferior to this is divided into anterior mediastinum which is in front of the anterior pericardium, the middle mediastinum which is the space between the anterior portion of the pericardium back to the anterior portion of the vertebral body, and the posterior mediastinum which is between the anterior portion of the vertebral body to the posterior portion of the vertebral body, i.e. to include the region of the paravertebral gutters. Tumors of the anterior mediastinum include thymoma, germ cell tumors (teratoma is one type), thyroid enlargement, and lymphoma. Middle mediastinal masses include pericardial cysts, bron-chogenic cysts, lymphoma and mediastinal granulomas. The posterior mediasti-nal masses are predominantly tumors of neurogenic origin.
Evaluation of mediastinal tumors commences with the history and physical examination. The history is very important because a history of chills and night sweats may be more consistent with lymphoma rather than thymoma or germ cell tumor, for example. Physical examination, including a good systemic examination, is performed. Laboratories including alpha-fetoprotein and beta HCG for anterior mediastinal tumors, as well as catecholamine levels and urinary VMA levels are important for posterior mediastinal tumors.
There are three approaches for tissue assessment of mediastinal tumors: Percutaneous needle aspiration; mediastinoscopy; and anterior mediastinotomy (Chamberlain procedure). In general, needle aspiration biopsy of presumed thy-momas is contraindicated because of the possibility of seeding the mediastinum or pleura. Mediastinoscopy is excellent for evaluating adenopathy in the mediastinum including diagnosis of a lymphoma. It has some anatomic limitations in that it does not permit access to the anterior mediastinum, the aortopulmonary window region, or the posterior subcarinal region. An anterior mediastinoscopy will provide access to the anterior mediastinum and to the aortopulmonary window region. All mediastinal tumors require investigation by CT for evaluation of the lesion itself, as well to evaluate invasion of surrounding structures. A mediastinal tumor which is suspected of having a vascular component should be investigated with angiography.
Fig 18.1. Mediastinal compartments.
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