1-Well defined epithelial lesions comprise 15-20% of all mediastinal masses.
2-Sharply defined wall.
Paper thin wall.
Clear fluid content(0-20 HU).
3-It can be differentiated from other cysts seen in other parts of the body in that the presence of septation and marginal calcification could be accepted as normal findings seen in a simple cyst and not as a complicated one.
4-No solid component or mural nodules and no enhancement( as we mentioned before the presence of a cyst containing mural nodule, wall enhancement or shows wall thickness deviate it from cystic lesion to a solid one).
5-If you see a cyst with the most of its parenchyma seen in the lung area while a small part of it is seen in the mediastinum, diagnose it as a mediastinal lesion and not as lung lesion, as it is very difficult to a lung cyst(benign and soft) to deviate into mediastinum, but it is very easy to a mediastinal cyst to merge from mediastinum to the lung area(this rule is not a typical in case of bronchogenic carcinoma).
1)Anterior mediastinal cyst = Pericardial cyst(related to right cardiophrenic angle).
D.D.from hydatid cyst:
-Pericardial cyst is mediastinal lesion causes lung compression but hydatid is a lung lesion do not cause lung compression.
-It is common in clinical practice to see pericardial cyst in the right cardiophrenic angle but not common to see hydatid cyst in such a position.
-In case of pericardial cyst, its border take the shape of heart border(mediastinal border as seen in CT image below).This could not be seen in hydatid cyst.
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| Pericardial cyst by chest X-ray |
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| Pericardial cyst by CT |
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| Pericardial cyst T1: here you can seen the mediastinal fat surrounding the cyst denoting that this cyst is in the mediastinum and not in the lung. |
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| Pericardial cyst T2 |
-Occur most common near the carina but usually occurs at any site.
-Usually protrude to the right side as Terato dermoid cyst.
-Presence of air in the cyst means occurrence of infection or tracheobronchial connection.
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| Bronchogenic cyst near tracheal bifurcation |
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| Bronchogenic cyst with fluid level |
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| Bronchogenic cyst with fluid level |
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| MRI T1 of a bronchogenic cyst surrounded by fat denoting its mediastinal origin |
3-Posterior mediastinal cyst: Esophageal duplication cyst: usually related to esophagus.
-Rare lesion.
-Fluid level means presence of infection or connection to esophagus.
-Difference between it and neuroenteric cyst is that the former is associated with vertebral anomalies.
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