Mediastinum


 * **Epidemiolgy:** || Thymomas Epidemiology: Thynomas account for 20% of medialstinal tumors in adults, and are the most common lesion found in the anterior mediastinum.

Mediastinal Germ Cell tumor Epidemiology: Represent only 3-10% of tumors originating in the mediastinum. 7 ||
 * **Etiology** || Thymomas Etiology: roughly 33% to 50% are associated with myasthenia gravis (a neuromuscular autoimmune disorder). Small percentages are related to both red cell aplasia and hypogammaglobulinemia.

Mediastinal Germ Cell tumor Etiology: Significantly more common in males, pure seminomas are most common in the third decade of life. Nonseminomatous germs cell tumors can occur from the ages of 15 to 35. 1 ||
 * **Signs & Symptoms:** || Thymomas Signs and symptoms:
 * Chest pain
 * Dysphagia
 * Weight loss
 * Anorexia
 * Hoarseness
 * Dyspena
 * Superior Vena Cava Syndrome syndrome (SVC): a condition, most common in lesions of the right lobe extending into the mediastinum, where the tumor puts pressure on the superior vena cava. This pressure can result in the inability to lie flat, swelling of the face neck and arm, cyanosis, and difficulty breathing. This condition will present during the regional phase. 2

Mediastinal Germ Cell tumor Signs and symptoms: *Spindle (depending on source) 1 || Table2 || Malignant Mediastinal Germ Cell Tumors: Tracheal Tumors: Grade: GX Grade cannot be assessed (Undetermined grade) G1 Well-differentiated (Low grade) G2 Moderately differentiated (Intermediate grade) G3 Poorly differentiated (High grade) G4 Undifferentiated (High grade) || Stage I: Completely encapsulated microscopically & no microscopic encapsulation Stage II: 1. Microscopic invasion into surrounding fatty tissue or pleura 2. Microscopic invasion into capsule Stage III: Microscopic invasion into adjacent organs Stage IV: A. Pleural or pericardial implants B. Lymphatogenous/hematogenous metastasis ||
 * In cases of benign teratomas and seminomas patients may be asymptomatic
 * Pain in the neck and arms (from substernal pressure)
 * Dyspnea
 * Cough
 * Hemoptysis
 * SVC ||
 * **Diagnostic Procedures:** || Table1[[image:uwlmedicaldosimetry2012/DSCN0928.JPG width="560" height="665"]] ||
 * **Histology:** || * Lymphocytic 1
 * Epithelial 1
 * Mixed (lymphoepithelial) 1
 * **Lymph node drainage:** || [[image:uwlmedicaldosimetry2012/DSCN0926.JPG width="480" height="398"]]
 * **Metastatic spread** || Thymomas:
 * 39%-64% of thyomas are non-invasive with the most common form of spread being direct invasion of surrounding critical structures
 * The most common area of metastatic spread is seen in the pleural cavity.
 * Other common sites of metastatic spread include the superior vena cava, brachial cephalic vein, the lungs, and the pericardium.
 * Distant mets are rare, but common sites include bone and the liver. 5
 * If metastatic disease is involved, lymph nodes are most commonly involved, including the middle and posterior mediastinal nodes along with the retroperitoneal nodes. 5
 * Approximately 33% of tracheal cases have metastatic involvement at diagnosis.
 * Frequency of metastatic spread depends on the histology of the tracheal tumors.
 * The main route of spread for tracheal tumors is to regional lymph nodes.
 * Spread also occurs through direct extension into surrounding critical structures and distant metastases include the liver and bone. 5 ||
 * **Grading:** || The American Joint Commission on Cancer recommends the following guidelines for grading tumors: 6
 * **Staging:** || Masaoka Thymic Staging System: 6
 * **Radiation side effects:** || Mediastinal iradiation may cause acute symptoms which include fatgue, transient skin reactions, cough, dysphagia, and dyspnea. Cardiac toxicities such as coronary artery disease, and restricted myopathy may develop. Other late toxicities include mucosal fibrosis, radiation-induced osteoporosis with possible rib fracture, and radiation myelitis. Younger patients may develop radiation-induced secondary neoplasms. Female patients may develop breast cancer. 4 ||
 * **Prognosis:** || ** Thymoma Prognostic Factors ** 3
 * Invasiveness (stage of disease)
 * Completeness of resection of tumor
 * Autoimmune diseases
 * Age
 * Mediastinal Germ Cell Tumor Prognostic Factors ** 3
 * Histologic type
 * Extrathoracic involvement
 * Superior vena cava syndrome
 * Lymphadenopathy
 * Hilar disease
 * Incomplete resection ||
 * **Treatments:** || The prefered method of treatment is surgery, followed by radiation therapy for stage II tumors. For stage III and IV tumors, a multimodality approach including chemotherapy can be used. 4

Typical radiation doses range from 30 to 60 Gy given in 1.8 or 2.0 Gy per fraction. Postoperative dose after thymoma resection is 45 to 50 Gy in 1.8 to 2.0 Gy per fraction. For microscopically positive resection margins and grossly positive margins, doses of 54 and 60 Gy, respectively, can be administered. 3

Typical volumes treated should include the entire thymus or tumor bed, mediastinum, and part of involved adjacent lung, plus a 2 cm margin. Treatment portals may include single anterior field, opposed anterior-posterior fields, wedge pair, and multifield arrangments. 3 || Image courtesy of: Nocolaou N. Prevention and Management of Radiation Toxicity. In: Pazdur R, Coia LR, Hoskins WJ, Wagman LD, eds. Cancer Management: A Multidisciplinary approach [e-book]. 10th ed. CMPMedica; 2007. Available from: CancerNetwork. Accessed June 4, 2012. ||
 * **TD 5/5:** || To minimize cardiotoxicity, the volume of the heart recieving 25 Gy or more should be less than 50% of the cardiac volume. Lung tolerances using V20 and V5 should be applied. 4
 * **References:** || # Chao KC, Perez CA, Brady LW. Radiation Oncology Management Decisions. 3rd ed. Philadelphia, PA; Lippincott Williams & Wilkins. 2011: 341-345.
 * 1) Washington CM. Principles and Practice of Radiation Therapy. 3rd ed. St. Louis, Missouri; Mosby Inc: 402.
 * 2) Perez CA, Brady LA, Halpern EC, Schmidt-Ullrich RK. Principles and Practice of Radiation Oncology. 4th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2004.
 * 3) Hoppe RT, Phillips TL, Mack III M. Leibel and Phillips Textbook of Radiation Oncology. 3rd ed. Philadelphia Pa: Elsevier Saunders; 2010.
 * 4) Chao KC, Perez CA, Brady LW. //Radiation Oncology Management Decisions//. 3rd ed. Philadelphia, PA; Lippincott Williams & Wilkins. 2011:305-320.
 * 5) MedicineNet. Tumor grade. Available at: []. Accessed June 5, 2012.
 * 6) Malignant Mediastinal Germ Cell Tumors. Available at:[] .Accessed June 9 2012 ||

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