Mediastinal tumors are among the most difficult lesions examined by the surgical pathologist for several reasons. First, many different types of lesions occur in this location (figure 1 and figure 2). Second, biopsies often consist of small, crushed specimens. Third, few pathologists have significant experience with mediastinal pathology because specimens from this location are relatively uncommon.
Since many tumors that occur in the mediastinum are undifferentiated and have overlapping histologic features, one must consider a broad differential diagnosis and perform a thorough evaluation of each biopsy specimen. This is particularly important since appropriate therapy for various mediastinal tumors differs considerably and may significantly impact survival. Additionally, it may not be apparent whether the tumor actually arises in the mediastinum or from adjacent lung.
The pathology of mediastinal tumors is reviewed here. The clinical evaluation of mediastinal masses is discussed elsewhere, and clinical and management issues of the specific tumor types are reviewed in the relevant topics. (See "Evaluation of mediastinal masses".)
EXAMINATION OF SPECIMENS
One of the most difficult problems in the diagnosis of mediastinal tumors can be obtaining an adequate biopsy specimen. As some mediastinal tumors are not treated surgically (eg, lymphoma), diagnosis is often attempted with needle core or minimally invasive surgical biopsies. Biopsies may be non-diagnostic because the lesion is not sampled adequately or because crush artifact or extensive necrosis, fibrosis, or cystic change obscures the diagnostic lesion. (See "Evaluation of mediastinal masses".)
Intraoperative frozen sections are often used in the setting of surgical procedures: