cyst of the thymus

School ager
with respiratory distressCXR AP shows an abnormal contour to the left superior mediastinum in the region of the aortic arch which is too prominent for the patient’s age. Axial CT with contrast of the chest shows a low density lesion within the thymus compressing the brachiocephalic vein.The diagnosis was thymic cyst.
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Cervical
thymic cyst in an adult. Well-defined, homogeneous non-enhancing mass in the lower left anterior part of the neck, located medially to the sternoclediomastoid and anteriorly to the left common carotid artery and jugular vein.
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Cervical
thymic cyst in an adult. Image showing no relationship between the cystic mass (yellow arrow) and lower pole of the left thyroid lobe (blue arrow).
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Thyroglossal
duct pathology and mimics. Thymic Cyst. Axial contrast-enhanced CT image demonstrates a cystic mass (asterisk) in the left neck base between the right and left common carotid arteries (arrowhead), extending into the superior mediastinum. Bilateral subclavian arteries are also visualized (arrows)
insightsimaging.springeropen.com • CC-by-4.0
A diagnostic
approach to the mediastinal masses. Conventional radiograph can provide information pertaining to the size, anatomical location and density of a central mass. Right: Frontal chest radiograph shows a sharply defined area of increased opacity with a loss of the cardiac silhouette at the border of the right side of the heart (*). Contrast-enhanced CT scan reveals a thin-walled water-attenuation lesion (*) in the right cardiophrenic angle (pericardial cyst). Middle: Lateral chest radiograph and contrast-enhanced CT scan show a unilocular, well-defined and homogeneously hypodense mass in the anterior mediastinum with peripheral calcification (open arrows) (thymic cyst). Left: Chest radiograph shows the aortopulmonary window with an abnormal convex border (arrow). Contrast-enhanced CT scan demonstrates a multilobulated mass in the anterior mediastinum (arrow), which accounts for the distortion of the AP window (nodular sclerosis Hodgkin disease)
insightsimaging.springeropen.com • CC-by-2.0
A diagnostic
approach to the mediastinal masses. A well-marginated mass with a homogeneous attenuation, usually in the range of water attenuation (0–20 HU) and without an enhancement of the wall or infiltrative appearance are the typical features of benign mediastinal cysts. Probably thymic cystic (a) and pericardial cyst (b)
insightsimaging.springeropen.com • CC-by-2.0
A diagnostic
approach to the mediastinal masses. Congenital thymic cyst in a 47-year-old man. Contrast-enhanced CT scan demonstrates a unilocular unenhanced lesion in the anterior mediastinum which shows a homogeneous fluid-attenuation (arrow)
insightsimaging.springeropen.com • CC-by-2.0
A diagnostic
approach to the mediastinal masses. Acquired thymic cyst in a 43-year-old man. a Contrast-enhanced CT scan shows a well-defined water-attenuation multiloculated mass (*) in the anterior mediastinum. b Sagittal T2-weighted MR sequence demonstrates a multiloculated mass with typical high signal intensitiy and fine internal septa within (arrow)
insightsimaging.springeropen.com • CC-by-2.0
Role of
different imaging modalities in the evaluation of normal and diseased thymus. Sixty-year-old male patient complaining of dyspnea. a Reconstruction image showing right-sided opacity not silhouetting the cardiac border. b–d Contrast-enhanced axial CT chest mediastinal and lung windows showing anterior mediastinal fluid attenuating non-enhancing cystic lesion. It shows a thin rim with no enhancement. CT diagnosis and histopathological confirmation revealed “thymic cyst”
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Radiopaedia • CC-by-nc-sa 3.0 • de

Thymic cysts are cysts that occur within or arise from the thymus.

Epidemiology

Thymic cysts are uncommon lesions and are estimated to account for approximately 1-3% of all anterior mediastinal masses . They are however reported to be the second most common type of primary mediastinal cyst .

Clinical presentation

A large proportion of patients with thymic cysts (i.e. around 60%) are considered to be asymptomatic. Approximately 50% of congenital thymic cysts are incidentally discovered during the first 2 decades of life. Acquired cysts may present much later. If symptoms are present, the most common have to reported to be cough, dyspnea, and chest pain .

Pathology

The presence of Hassall's corpuscles in the cyst wall is diagnostic, especially in congenital lesions. The cysts often contain turbid fluid or gelatinous material.

They can be seen in a variety of settings:

  • congenital: 
    • contains thymic tissue in their wall
    • often unilocular
    • rare and derive from a patent thymopharyngeal duct.
  • acquired: often multilocular
    • secondary to thoracotomy
    • following chemotherapy or radiotherapy for mediastinal/intrathoracic malignancy
    • inflammatory
    • in association with thymic tumors
    • may be unilocular or multilocular
      • multilocular thymic cysts are the sequelae of a variety of inflammatory processes and usually occur in asymptomatic men
Location

Can be broadly divided into:

  • cervical: cervical thymic cyst (CTC)
  • mediastinal/thoracic: mediastinal thymic cyst (MTC)

Larger lesions can sometimes occur in combination.

Associations

Large multilocular thymic cysts are seen in approximately 1% of children with human immunodeficiency virus infection .

Radiographic features 

Thymic cysts can fluctuate both in size and attenuation over time on CT and MRI.

Plain radiograph

May not even be visible (especially small lesions). If visible thymic cysts often indistinguishable from other non-lobulated thymic/anterior mediastinal lesions on radiographs.

CT

Typically manifests as unilocular or multilocular cystic masses with well-defined walls. Lesions can be lobulated and may have soft-tissue attenuation components. Some thymic cysts may have increased CT attenuation if hemorrhage or infection occurs as a complication. Curvilinear calcification of the cyst wall occurs in a small proportion of cases. According to one study, cysts had a mean attenuation value of around 23 HU and a maximal attenuation value of 58 HU.

MRI

In uncomplicated cases, signal characteristics are similar to any simple cyst and are:

  • T1: low signal
  • T2: high signal 
  • T1 C+ (Gd): no intrinsic enhancement

If hemorrhage or infection occurs, the cysts can demonstrate high signal intensity on both T1 and T2-weighted images and are also referred to as complicated cysts.

Differential diagnosis

See also

Siehe auch:
und weiter:
Assoziationen und Differentialdiagnosen zu Thymuszyste:
cystic
mediastinal masses
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mediastinales
Teratom
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primäre
Thymusneoplasien
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lymphatische
Malformationen
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