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INTRODUCTION

Mediastinal masses encompass a diverse spectrum of solid tumors, vascular abnormalities, and cysts, arising from and associated with each of the structures found within the mediastinum.1–4 Cystic lesions account for up to 25% of reported mediastinal masses.1,3–5 These cysts may be congenital or acquired, or they may represent cystic degeneration of a previously solid tumor. In this chapter, we focus on congenital cystic lesions within the mediastinum, specifically addressing foregut cysts including bronchogenic cysts, enterogenous (esophageal duplication) cysts, and neurenteric cysts. Together, they constitute up to 9% of all primary mediastinal masses. We will also briefly consider simple cysts arising from the thymus, pericardium, and thoracic duct. Many other solid mediastinal neoplasms (dermoids, teratomas, thymomas, parathyroid adenomas, and thyroid goiters) may present with cystic components. These lesions are discussed separately in Chapter 82.

ANATOMY

Cysts may arise in each of the three anatomic compartments of the mediastinum. The boundaries of these compartments, based on cross-sectional imaging, were recently codified by the International Thymic Malignancy Interest Group, with small but significant changes to previous descriptions.6–9

The prevascular compartment is bounded superiorly by the thoracic inlet, inferiorly by the diaphragm, laterally by the parietal mediastinal pleura, anteriorly by the sternum, and posteriorly by the anterior aspect of the pericardium, as it wraps around the heart and vessels in a curvilinear fashion. Thymic cysts and endocrine lesions, such as thyroid goiters and cystic adenomas of the parathyroid gland, are found in this compartment.6,7

The visceral compartment is the site of origin of most congenital foregut cysts. The boundaries of the visceral compartment include the thoracic inlet superiorly and the diaphragm inferiorly. The anterior border is the anterior aspect of the pericardium as it wraps around the heart and vessels in curvilinear fashion. The posterior border is defined as a vertical line transecting each thoracic vertebrae 1 cm posterior to its anterior margin. Bronchogenic cysts, enterogenous cysts, pericardial cysts, and thoracic duct cysts arise in this compartment.6,7

The paravertebral compartment also extends from the thoracic inlet superiorly to the diaphragm inferiorly. The anterior border is the “visceral-paravertebral compartment boundary line” (1 cm posterior to the anterior margins of the vertebrae). The posterolateral margin is defined as the vertical line against the posterior margin of the chest wall at the lateral margin of the transverse processes of the thoracic spine. The paravertebral compartment includes both costovertebral sulci and segmental nerve roots, as well as the sympathetic chain and paravertebral soft tissues. Neurenteric cysts arise within this compartment.6,7

It is important to note that lesions that arise primarily within the mediastinum may also extend above the chest into the neck or below the diaphragm into the retroperitoneum, where they present as extrathoracic mass lesions. In addition, cysts within one mediastinal compartment may ...

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