Thymic cysts are cysts that occur within, or arise from, the thymus.
Thymic cysts are uncommon lesions and are estimated to account for approximately 1-3% of all anterior mediastinal masses 4. Approximately 50% of congenital thymic cysts are incidentally discovered during the first 2 decades of life. Acquired cysts may present much later.
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:
- contains thymic tissue in their wall
- often unilocular
- rare and derive from a patent thymopharyngeal duct.
- acquired: often multi locular
- secondary to thoracotomy
- following chemotherapy or radiotherapy for mediastinal malignancy
- in association with thymic tumours
- may be unilocular or multilocular
- multilocular thymic cysts are the sequelae of a variety of inflammatory processes and usually occur in asymptomatic men
Can be broadly divided into:
Larger lesions can sometimes occur in combination.
Large multilocular thymic cysts are seen in approximately 1% of children with human immunodeficiency virus infection 5.
May not even be visible (especially small lesions). If visible thymic cysts often indistinguishable from other non-lobulated thymic -anterior mediastinal lesions on radiographs.
Typically manifest 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 haemorrhage or infection occurs as a complication. Curvilinear calcification of the cyst wall occurs in a small proportion of cases.
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.
If cervical consider
- branchial cleft cyst: any type dependant on location
If mediastinal consider
- 1. Brown LR, Aughenbaugh GL. Masses of the anterior mediastinum: CT and MR imaging. AJR Am J Roentgenol. 1991;157 (6): 1171-80. AJR Am J Roentgenol (abstract) - Pubmed citation
- 2. Moskowitz PS, Noon MA, Mcalister WH et-al. Thymic cyst hemorrhage: a cause of acute, symptomatic mediastinal widening in children with aplastic anemia. AJR Am J Roentgenol. 1980;134 (4): 832-6. AJR Am J Roentgenol (citation) - Pubmed citation
- 3. Zhang M, Endo M, Adachi S et-al. Multilocular thymic cyst: MR findings. AJR Am J Roentgenol. 1994;163 (2): 479-80. AJR Am J Roentgenol (citation) - Pubmed citation
- 4. Choi YW, Mcadams HP, Jeon SC et-al. Idiopathic multilocular thymic cyst: CT features with clinical and histopathologic correlation. AJR Am J Roentgenol. 2001;177 (4): 881-5. AJR Am J Roentgenol (full text) - Pubmed citation
- 5. McErlean A, Huang J, Zabor EC, Moskowitz CS, Ginsberg MS. Distinguishing benign thymic lesions from early-stage thymic malignancies on computed tomography. Journal of thoracic oncology : official publication of the International Association for the Study of Lung Cancer. 8 (7): 967-73. doi:10.1097/JTO.0b013e3182904bc2 - Pubmed
- 6. Jeung MY, Gasser B, Gangi A, Bogorin A, Charneau D, Wihlm JM, Dietemann JL, Roy C. Imaging of cystic masses of the mediastinum. Radiographics : a review publication of the Radiological Society of North America, Inc. 22 Spec No: S79-93. doi:10.1148/radiographics.22.suppl_1.g02oc09s79 - Pubmed