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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%)

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Myasthenia Gravis (MG)

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

    • Decreased number of acetylcholine receptors at neuromuscular junctions

    • Believed to be autoimmune process

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Epidemiology

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  • • 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

      -Hypogammaglobulinemias

      -Autoimmune diseases, such as rheumatoid arthritis and lupus

    • MG is more commonly associated with lymphocytic variety

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Symptoms and Signs

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  • • 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

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Laboratory Findings

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  • • MG

    • -90% have serum antibodies against acetylcholine receptors

      -70% have germinal center formation on thymic biopsy

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Imaging Findings

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  • Chest film: Anterior mediastinal mass

    CT scan: Useful in assessing extent of lesion

    MRI: Can assess vascular invasion

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  • 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

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Rule Out

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  • • Lymphoma

    • -Can be difficult to differentiate histologically from thymoma

    • Thymic carcinoma

    • -Very aggressive variant of thymic lesions

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  • • Tissue histology necessary to make diagnosis

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Surgery

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  • • 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

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Indications

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  • • 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

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Contraindications

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  • • Lymphoma not indication for thymectomy

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Medications

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  • • Postoperative radiation therapy indicated for stage II

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Myasthenia Gravis (MG)

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  • • 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

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Treatment Monitoring

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  • • Response rate exceeds 70% with chemotherapy

    • 75% of patients with MG improve after thymectomy

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Complications

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  • • Thymyectomy complications are low, except ...

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