Thymolipoma
Summary
Benign thymic mass composed of mature fat plus thymic tissue. Often very large and pliable, so it can drape over the heart and mimic cardiomegaly on CXR.
Epidemiology and clinical
- Rare overall; reported around 2% to 9% of thymic tumours
- Any age, often discovered in adults
- Frequently asymptomatic; symptoms are usually from mass effect when giant
Associations
- Reported with Myasthenia gravis and other autoimmune phenomena, but not a reliable pairing
Imaging
CXR
- Apparent cardiomegaly or anterior mediastinal opacity
- Can “slump” toward the diaphragm and conform to the cardiac silhouette
CT (most helpful)
- Predominantly fat attenuation anterior mediastinal mass
- Internal soft tissue strands/nodules representing thymic tissue
- Usually well-defined and non-invasive in behaviour
MRI
- Fat signal: high T1/T2, suppresses on fat-sat
- Thymic soft tissue components may enhance
Key differentials
- Mediastinal lipoma: almost pure fat, minimal soft tissue
- Teratoma: fat plus calcification/fluid, more mixed elements
- Well-differentiated liposarcoma: thicker septa, nodular non-fat soft tissue, more aggressive features
- Prominent pericardial fat pad / Morgagni hernia: check continuity with abdomen or typical location
