Key Points

• Mediastinal masses are uncommon, with mediastinal cysts accounting for 20% of such masses.
• Confusion regarding mediastinal cysts and duplications is, in large part, due to the plethora of ambiguous names associated with this entity.
• Bronchogenic cysts are commonly symptomatic in contrast to esophageal cysts, which are asymptomatic.
• Complete excision is the treatment of choice and is indicated in most patients for increasing size or treatment of symptoms or complications.
• Resection can often be done using minimally invasive techniques; however, largely due to associated inflammatory changes, open techniques may be necessary.

Mediastinal masses are relatively uncommon disorders that remain an interesting diagnostic and therapeutic challenge for thoracic surgeons. Cysts account for approximately 20% of all such masses. A review of all surgically treated mediastinal masses at the Mayo Clinic over a 40-year period revealed that 18.4% were cystic.[1] Similarly, in a series of 400 consecutive patients with primary lesions of the mediastinum, 99 (25%) had a primary cystic lesion.[2] Furthermore, these same authors identified a combined total of 2799 patients with mediastinal lesions with cysts representing 9% to 26% of mediastinal lesions.[2] Finally, Oldham found in a collection of 214 mediastinal cysts from 5 separate authors that 41% were bronchogenic, 35% were pericardial, 10% were enteric, and 14% were nonspecific.[3]

The terms describing mediastinal cysts have been plagued by ambiguity resulting in confusion. Mediastinal cysts have been alternatively called bronchogenic, bronchoesophageal, enteric, enterogenous, esophageal, and duplication cysts.[4] Difficulty with the classification arises because theoretically all tissue types within the mediastinum may become cystic, and thus classification based solely on location can be misleading. For example, bronchogenic cysts are usually in the subcarinal or peritracheobronchial areas associated with the major airways, esophagus, or cardiac structures; however, bronchogenic cysts may also occur within the lung parenchyma. The term duplication is confusing because it is not descriptive of the cyst’s origin. Maier, in 1948, used the cyst’s anatomic location to differentiate these lesions.[5] Others have used the histology of the epithelial lining as the defining characteristic. Fallon and associates, in 1954, utilized the cyst’s embryologic origin as well as the anatomic location to classify these lesions.[6]

This chapter focuses on bronchogenic, esophageal (duplication), neurenteric, pericardial, thymic, thoracic duct, pancreatic, and parathyroid cysts, which will be individually discussed. Because most mediastinal cysts are congenital in origin and embryologic development is an important factor in classification, we will focus first on a brief review of the development of the lung and esophagus.