Thymolipoma is a rare, benign anterior mediastinal mass of thymic origin, containing both thymic and mature adipose tissue.
Thymolipomas comprise ~5% (range 2-9%) of all thymic neoplasms, but are less common than a mediastinal lipoma of non-thymic origin. There is no recognised sex predilection and reported age range between 3-56 years, with a mean age of 22 years.
Most thymolipomas are asymptomatic and found incidentally, often due to imaging of respiratory tract infection 1. Symptoms, when present are attributable to displacement of mediastinal structures. Approximately 25% complain of non-specific symptoms such as cough, dyspnoea and chest pain, which may or may not be the result of the mass.
Thymolipomas are composed of a mixture mature adipose tissue with islands of thiymic tissue. The aetiology remains uncertain, with hypotheses proposed including 1
- true neoplasm of the thymus
- variant of a thymoma
- hyperplasia of mediastinal fat
- neoplasm of mediastinal fat which engulfs thymic tissue
Irrespective of cause, these tumours are slow-growing, only gradually increasing in size and are usually large at the time of diagnosis.
- aplastic anemia
- Graves disease
- Hodgkin lymphoma
- chronic lymphocytic leukaemia
They occur mostly in the cardiophrenic angles.
A thymolipoma can grow to a very large size before discovery.
Typically these tumours appear as large anterior mediastinal masses. The larger tumours tend to hang down one or either side of the pericardium, and being soft, they mold themselves to the adjacent mediastinum and diaphragm and often mimic cardiomegaly 1. The predominantly fat density can be difficult to identify on plain radiography, however in larger masses that abut the diaphragm, the diaphragm can still be seen.
On CT thymolipomas typically appears almost entirely fatty with some areas of inhomogeneous soft tissue density that represent thymic tissue.
Thymolipomas have fat and soft tissue signal characteristics:
- T1: typically the adipose tissue within the tumour returns high T1 signal and thymic component a more intermediate T1 signal
- STIR FS: shows complete suppression; consistent with subcutaneous fat
Treatment and prognosis
Surgically local resection curative, no reports of recurrence, metastasis or mortality.
History and etymology
First reported by Lange in 1916. The term was coined by Hall in 1948.
On CT the differential is much narrower and includes
- 1. Rosado-de-christenson ML, Pugatch RD, Moran CA et-al. Thymolipoma: analysis of 27 cases. Radiology. 1994;193 (1): 121-6. Radiology (abstract) - Pubmed citation
- 2. Casullo J, Palayew MJ, Lisbona A. General case of the day. Thymolipoma. Radiographics. 1992;12 (6): 1250-4. Radiographics (citation) - Pubmed citation
- 3. Gamanagatti S, Sharma R, Hatimota P et-al. Giant thymolipoma. AJR Am J Roentgenol. 2005;185 (1): 283-4. AJR Am J Roentgenol (full text) - Pubmed citation