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  • • Thymic tumors occur in anterior mediastinum and include thymomas, lymphomas, Hodgkin lymphoma

    • Most common type often difficult to distinguish from lymphoma

    • 3 predominant cell types

    • -Lymphocytic (25%)

      -Epithelial (25%)

      -Lymphoepithelial (50%)

Myasthenia Gravis (MG)

  • • Neuromuscular disorder characterized by weakness and fatigability of voluntary muscles

    • Decreased number of acetylcholine receptors at neuromuscular junctions

    • Believed to be autoimmune process


  • • 30% of patients with thymoma have MG

    • Thymoma develops in 15% of patients with MG

    • Thymomas associated with paraneoplastic syndromes including:

    • -Cytopenias

      -Red cell aplasias


      -Autoimmune diseases, such as rheumatoid arthritis and lupus

    • MG is more commonly associated with lymphocytic variety

Symptoms and Signs

  • • 50% of asymptomatic cases identified on chest film

    • Chest pain dysphagia, MG, dyspnea, or superior vena cava syndrome most common if symptomatic

    • Easy fatigability in patients with MG

Laboratory Findings

  • • MG

    • -90% have serum antibodies against acetylcholine receptors

      -70% have germinal center formation on thymic biopsy

Imaging Findings

  • Chest film: Anterior mediastinal mass

    CT scan: Useful in assessing extent of lesion

    MRI: Can assess vascular invasion

  • Myasthenia Gravis (MG): Decremental response in muscular contraction to repeated stimulation with improvement after edrophonium administration (short-acting anticholinesterase)

    Definitive diagnosis: Histologic tissue analysis

    • Do not biopsy small, well-encapsulated mediastinal masses

    • Complete excision, otherwise risk tumor seeding

Rule Out

  • • Lymphoma

    • -Can be difficult to differentiate histologically from thymoma

    • Thymic carcinoma

    • -Very aggressive variant of thymic lesions

  • • Tissue histology necessary to make diagnosis


  • • Treatment of choice for thymoma is total thymectomy

    • Performed via median sternotomy, trap door, or clamshell approach

    • Cervical incision not useful for malignant disease, only for benign disease


  • • Stages I, II, III should be aggressively resected

    • En bloc resection with associated structures is warranted if complete resection is possible

    • Large (> 5 cm) neoadjuvant chemotherapy may shrink tumor

    • Large lesions with gross invasion-biopsy to confirm histologic diagnosis, then neoadjuvant therapy prior to resection

    • MG indication for early thymectomy


  • • Lymphoma not indication for thymectomy


  • • Postoperative radiation therapy indicated for stage II

Myasthenia Gravis (MG)

  • • Anticholinesterase drugs initial treatment and used aggressively in postoperative period

    • Corticosteroids used in select cases

    • Plasmapheresis can minimize need for anticholinesterase agents

    • Avoid muscle relaxants and atropine

Treatment Monitoring

  • • Response rate exceeds 70% with chemotherapy

    • 75% of patients with MG improve after thymectomy

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