대한흉부영상의학회 Korean Society of Thoracic Radiology

Discussion

Diagnosis With Brief Discussion

Diagnosis

Thymic Cyst

Radiologic Findings

Chest PA shows homogeneous opacity involving over two thirds of the right hemithorax with convex upper margin on lateral view. Fluid shifting is not seen on decubitus view.
Chest CT scan shows huge thin-walled cystic mass in right hemithorax with mediastinal shifting and passive atelectasis of middle and lower lobe collapse.

Brief Review

Thymic cysts are uncommon mediastinal lesions that account for only 1% to 2% of all tumors in the anterior mediastinum. It can be either congenital or acquired.
It has been suggested that most of them are probably derived from remnants of the fetal thymopharyngeal duct.

Pathologically, the cysts are unilocular or multilocular and range in size from microscopic to as large as 18cm in maximal diameter.
Histologically, the cyst wall is lined by squamous, transitional, or simple cuboidal or columnar epithelium.
Thymic tissue can be identified focally in the cyst wall and , in fact, is necessary to make the diagnosis.
An important point in pathologic differential diagnosis is the observation that
some malignant tumors, including thymoma, Hodgkin's disease, and germ cell tumors, can show prominent cystic change, occasionally associated with a relatively small amount of neoplastic tissue; consequently, thorough sampling of every thymic cyst must be carried out to exclude the possibility of neoplasia, especially if the cyst wall is focally thickened.

On CT, thymic cysts typically have water density and thin walls.
Occasionally, soft tissue septa or ringlike calcifications are seen within the cyst or foci of linear calcification in the cyst wall, presumably as a result of previous hemorrhage.
Most patients are asymptomatic. The prognosis is excellent.

References

Fraser and Pare's ; Diagnosis of diseases of the chest. 4th ed. 1999. W. B. saunders company

Keywords

Mediastinum, Benign tumor,