May Be Caused by

 Common

Bronchogenic cyst

Duplication cyst

Fluid-filled esophagus

Hiatal hernia

Hydatid cyst

Lymphoma

Neurenteric cyst

Neurogenic tumor

Paraspinal abscess

Pericardial cyst

Pericardial effusion

Teratoma

Thymic cyst

Thymoma

 Uncommon

Ascites extending through esophageal hiatus

Esophagectomy with gastric or colon interposition

Loculated paramediastinal pleural effusion

Lymphangioma

Lymphocele

Meningocele

Myelomeningocele

Pancreatic pseudocyst

Perforated central venous catheter

Seroma