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