Management of Mild Thymic Hyperplasia
Therapeutic intervention is usually not required for mild thymic hyperplasia, particularly if the lesion is less than 30mm, given the low risk of progression or malignancy. 1
Diagnostic Confirmation
Before deciding on observation versus intervention, proper characterization is essential:
- CT imaging with IV contrast is the standard initial modality to assess thymic lesions 1
- Chemical-shift MRI should be obtained if CT findings are equivocal, as it can detect microscopic fatty infiltration characteristic of hyperplasia (showing homogeneous signal decrease on opposed-phase images) that is not observed in thymoma 1
- PET scanning is not recommended for thymic mass assessment, as thymic hyperplasia can show hypermetabolism similar to malignant lesions 1
Size-Based Treatment Algorithm
The 30mm threshold is critical for management decisions:
Lesions <30mm (Mild Hyperplasia)
- Observation without therapeutic intervention is the recommended approach 1
- No biopsy is required 1
- Imaging surveillance to confirm stability
Lesions ≥30mm
- Surgical resection becomes necessary due to increased risk of progression or malignancy 2, 3
- Complete thymectomy (including residual thymus gland and perithymic fat) via median sternotomy is the preferred surgical approach 1, 2
Clinical Context Considerations
Identify potential underlying causes that may influence management:
- Rebound hyperplasia should be considered after stress, injuries, chemotherapy, radiotherapy, anti-hormonal treatment, or corticosteroids 1
- Lymphoid hyperplasia is most commonly associated with myasthenia gravis, hyperthyroidism (particularly Graves' disease), connective tissue disease, or vascular disease 1, 4
- Systematic immunological workup is recommended including complete blood count with reticulocytes, serum protein electrophoresis, anti-acetylcholine receptor antibodies, and anti-nuclear antibodies 1
Imaging Features Supporting Hyperplasia Diagnosis
On CT, thymic hyperplasia typically demonstrates:
- Low-attenuation, symmetric appearance 1
- Fatty pattern maintaining the bi-pyramidal shape of the thymus 1
- Preservation of normal thymic architecture 5, 6, 7
Common Pitfalls to Avoid
- Do not pursue biopsy for small lesions (<30mm) with imaging characteristics consistent with hyperplasia, as this adds unnecessary risk without changing management 1
- Do not rely on PET avidity to distinguish hyperplasia from malignancy, as both can show increased uptake 1
- Avoid misdiagnosing lymphocyte-rich thymoma as hyperplasia—true hyperplasia maintains well-developed corticomedullary architecture with scattered Hassall corpuscles and no cytologic atypia 7
When Surgical Intervention Is Indicated
Surgery becomes necessary when: