Thymoma

Definition

· tumour of the epithelial component of the thymus
thymus sits in anterior mediastinum; posterior to sternum, anterior to pericardial sac

Epidemiology

· mean age of 50

Aetiology

· associated with a number of autoimmune disorders

— Myaesthenia Gravis

— aplastic anaemia

— SLE

--> 20% of myaesthenia gravis is associated with thymoma

— thymectomy has an unpredicatable effect on the MG in these cases

Pathophysiology

· myaesthenia gravis is muscle weakness and early fatigue 2° to antibodies to the ACh receptor on skeletal muscle

· usually affects the eyes, facial muscles and muscles of mastication

· diagnosed with the anticholinesterase EDROPHONIUM which transiently improves strength

· thymectomy is indicated with partial remission in 80% and total in 30%

· treatment with antichoinesterases (PYRIDOSTIGMINE) has variable effect

Pathology

· lobulated

· may be cystic

· most benign (80%)

· some with atypia are malignant and termed thymic carcinoma

· cytokeratin markers may be helpful in diagnosis

Clinical

· incidental XR finding

· pressure symptoms, chest pain, occasionally compression of airway, veins, phrenic or RLNs
Treatment

- Do not biopsy if reasonably resectable; dissemination risk
- Us. can be differentiated by radiologic apperance from other anterior mediastinal lesions and if parathymic syndromes, no BHCG or AFP (Germ cell tumours
- Resected via median sternotomy.
- Adjuvant therapy if invading beyond capsule; multomodal with meoadjuvant chemo and radiation therapy.

Prognosis

· 15% die of their tumour

· large size (>15cm); invasion of local structures or metastases are bad signs