Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content + • 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 +++ Epidemiology + • 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 +++ 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 +++ Surgery + • 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 +++ Indications + • 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 +++ Contraindications + • Lymphoma not indication for thymectomy +++ Medications + • 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 ... Your Access profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Password? Forgot Username? Sign in via OpenAthens Sign in via Shibboleth