The anterior mediastinal compartment plays host to a number of unique pathologies, both benign and malignant. In many circumstances, the tumors may be quite large prior to detection, whereupon extrinsic compression of other mediastinal structures leads to significant symptomatology. Alternatively, small-volume disease may be seen incidentally when cross-sectional imaging is performed for alternate and unrelated symptoms. Last, a number of disease processes of the anterior mediastinum manifest secondary to biochemical activity in the form of paraneoplastic/immunologic syndromes. Whatever the presentation, accurate delineation of the specific underlying disease process is essential to determining the appropriate treatment strategy.
Unlike other common neoplastic pathologies of the chest (lung, esophagus), clearly defined and potentially modifiable risk factors for malignancy tend not to be relevant with respect to anterior mediastinal disease processes. In that context, understanding the unique demographic profiles of patients presenting with anterior mediastinal pathology allows for a focused diagnostic approach and limits the often costly utilization of unnecessary studies.1 The mediastinum is generally divided into three separate compartments (anterior, middle, and posterior), the anatomic boundaries of which have been previously described. In the modern era, the definitions are based primarily on criteria identified on cross-sectional imaging.2 Taken together, roughly half of all mediastinal masses are located in the anterior mediastinum, with the rest evenly split between the middle and posterior compartments. Upon further evaluation of those tumors of the anterior mediastinum, nearly 60% are malignant. This finding distinguishes the anterior from the middle and posterior spaces, where the incidence of malignancy is generally <25%.3 With such a high likelihood of malignancy, establishing a diagnosis in an efficient and timely manner is paramount. Bearing in mind the significant overlap in cross-sectional radiographic characteristics of typical anterior mediastinal pathology (i.e., germ cell, lymphoma, thymoma), CT alone is rarely diagnostic. Recognizing the need for standardization of the image-based evaluation of mediastinal tumors, the International Thymic Malignancy Interest Group (ITMIG) has published an algorithm to provide guidance to the diagnostic approach.1
Although the general diagnostic approach to anterior mediastinal mass is beyond the scope of this chapter, it is important to recognize that age and sex are often the two most relevant pieces of clinical information when evaluating a patient with a newly identified mediastinal lesion. The differential diagnosis of a new anterior mediastinal mass can be effectively narrowed with an understanding of the common demographic profiles of the various pathologies. Symptoms at presentation are relevant as well, since the likelihood of malignancy is increased in the presence of symptoms.3 Given the increasingly common incidental identification of lesions on cross-sectional imaging, the absence of symptoms should not necessarily reassure the clinician. A biochemical evaluation is often warranted, with laboratory studies including alpha-fetoprotein (AFP), β-human chorionic gonadotropin (β-hCG), and lactate dehydrogenase (LDH).
Thymic malignancies, primary seminomatous and non-seminomatous germ-cell tumors, and lymphoma are the most common primary malignant ...