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page1 Mediastinal Mass ANATOMY The mediastinum is a narrow, vertically oriented structure that resides between the medial parietal pleural layers of the lungs. Mediastinal Divisions superior anterior middle posterior The superior mediastinum : The space between the thoracic inlet and the superior aspect of the aortic arch All mediastinal structures above an imaginary line drawn between the sternal angle and the fourth thoracic intervertebral disk on the lateral chest The anterior mediastinum is the space anterior to the heart and great vessels on the lateral chest radiograph. It is bordered anteriorly by the sternum and posteriorly by the pericardium Anterior mediastinum: Internal mammary vessels Internal mammary and prevascular lymph nodes Thymus Middle mediastinum Heart and pericardium Ascending and transverse aorta Main and proximal right and left pulmonary arteries Confluence of pulmonary veins Superior and inferior vena cava Trachea and main bronchi Lymph nodes and fat within mediastinal : Posterior mediastinum Descending aorta Esophagus Azygos and hemiazygos veins Thoracic duct Sympathetic ganglia and intercostal Localize to the mediastinum The following characteristics indicate that a lesion originates within the mediastinum: Unlike lung lesions, a mediastinal mass will not contain air bronchograms. The margins with the lung will be obtuse. Mediastinal lines (azygoesophageal recess, anterior and posterior junction lines) will be disrupted. There can be associated spinal, costal or sternal abnormalities. LEFT: A lung mass abutts the mediastinal surface and creates acute angles with the lung. RIGHT: A mediastinal mass will sit under the surface of the mediastinum, creating obtuse angles with the lung. On the x-ray on the left there is a lesion that has an acute border with the mediastinum. This must be a lung mass (pancoast tumor) The chest radiograph on the right shows a lesion with an obtuse angle to the mediastinum. This must be a mediastinal mass( thymoma ) . Utility of MDCT, MR, and PET in the Evaluation of :Mediastinal Masses MDCT = MR Confirming the presence of a mass versus tortuous vascular structure Localization of mass to anterior, middle, or posterior compartment Suspected aneurysm or vascular anomaly Detection of fluid MDCT = MR = US Detection of calcium CT Tracheal involvement MDCT > MR Involvement of spinal canal MR > MDCT Thoracic inlet lesions MR = MDCT Contraindication to iodinated contrast MR > MDCT Percutaneous biopsy of mediastinal mass CT ,US Thyroid Masses In a small percentage of patients with thyroid disease extension of the thyroid through the thoracic inlet into the superior mediastinum may occur. usually discovered as incidental findings on chest radiographs; a minority of patients will present with complaints of dyspnea or dysphagia Thyroid goiters arising from the lower pole of the thyroid or the thyroid isthmus can enter the superior mediastinum anterior to the trachea (80% of cases) or to the right and posterolateral to the trachea (20% of cases). : On chest radiographs An anterosuperior mediastinal mass typically deviates the trachea laterally and either posteriorly (anterior masses) or anteriorly (posterior masses) Radioiodine studies should be performed as the initial imaging procedure, although falsenegative results do occur. CT findings: (1) well-defined margins, (2) continuity of the mass with the cervical thyroid, (3) coarse calcifications, (4) cystic or necrotic areas, (5) baseline high CT attenuation (because of intrinsic iodine content), (6) intense enhancement (>25 H) and prolonged enhancement MR is useful in depicting the longitudinal extension of thyroid goiters without the use of intravenous contrast. Thymomas or thymic epithelial neoplasms Second most common primary mediastinal neoplasms in adults after lymphoma. Arise from thymic epithelium and contain varying numbers of intermixed lymphocytes. Traditional classification Thymomas, which are histologically benign but may be either encapsulated (noninvasive) or invasive, thymic carcinomas, in which the epithelial component shows signs of frank malignancy. WHO has recently classified these neoplasms based upon the morphology of the epithelial component and the ratio of epithelial cells to lymphocytes. The classification system divides these neoplasms into types A, AB, B1, B2, B3, and C, with a spectrum of histologic changes ranging from the classic encapsulated thymoma (A), to thymic carcinoma (C), The average age at diagnosis of thymoma is 45 to 50; Rare in patients under the age of 20. Most often associated with myasthenia gravis, Other autoimmune diseases associated with thymoma : pure red cell aplasia, Graves disease, Sjogren syndrome , hypogammaglobulinemia. Patients with myasthenia gravis, 10% to 28% have a thymoma, Patients with thymoma (30% to 54%) have or will develop myasthenia On chest radiographs, • Thymomas are seen as round or oval, smooth or lobulated soft tissue masses near the origin of the great vessels at the base of the heart CT is best for characterizing thymomas and detecting local invasion Higher-grade thymomas(types B3 and C) tend to show larger size, more irregular margins, heterogeneous enhancement, regions of necrosis, mediastinal nodal metastases, and calcification. Invasion of the thymic capsule 33% to 50% of patients. In the majority of these patients, this determination cannot be made by CT or MR . Local invasion of pleura, lung, pericardium, chest wall, diaphragm, and great vessels occurs in 10% to 15% of patients. . Contiguity of a thymoma with the adjacent chest wall or mediastinal structures cannot be used as reliable evidence of invasion of these structures. Drop metastases to dependent portions of the pleural space are a recognized Extrathoracic metastases are rare, Transdiaphragmatic spread of a pleural tumor into the retroperitoneum has been described. Tt is important to image the entire thorax and upper abdomen in any patient with suspected invasive disease : Thymic cyst May be congenital or acquired. Congenital unilocular thymic cysts are remnants of the thymopharyngeal duct. Acquired multilocular thymic cysts are postinflammatory associated with AIDS, prior radiation or surgery, and autoimmune conditions(myasthenia gravis,aplastic anemia,sjogren syndrom) in these latter conditions, clinical and radiologic distinction of multilocular thymic cyst from thymoma may be difficult two conditions can coexist Differentioal diagnose; cystic degeneration of a thymoma lymphoma germcell neoplasm lymphangioma The CT shows an anterior mediastinal mass with water density attenuation. This is typical for a thymic cyst. Thymic Carcinoid Neuroendocrine tumors of the thymus are rare malignant neoplasms arise from thymic cells of neural crest origin ([APUD] or Kulchitsky cells). The most common histologic type is carcinoid tumor, Ranges in differentiation and behavior from typical carcinoid to atypical carcinoid to small cell carcinoma. 40% of patients have Cushing syndrome The carcinoid syndrome is uncommon. This lesion is indistinguishable from thymoma on plain radiographs and CT scans. Thymic hyperplasia Enlargement of a thymus that is normal on gross and histologic examination. occurs primarily in children as a rebound effect in response to an antecedent stress, discontinuation of chemotherapy, or treatment of hypercortisolism. An association with Graves disease has also been noted Found in 60% of patients with myasthenia gravis. Most patients with thymic hyperplasia have normal or diffusely enlarged glands on CT : Thymic Lymphoma Thymus is involved in 40% to 50% of patients with the nodular sclerosing subtype of Hodgkin disease. Its radiographic appearance is indistinguishable from that of other solid neoplasms arising within the thymus. The presence of lymph node enlargement in other portions of the mediastinum or anterior Lymphoma Most common primary mediastinal neoplasm in adults. Hodgkin disease involves the thorax in 85% of patients at the time of presentation (25% of patients with limited to the mediastinum at the time of diagnosis). The majority (90%) of patients with intrathoracic involvement have mediastinal lymph node enlargement( most commonly involves the anterior mediastinal and hilar ) The anterior mediastinum is the most frequent site of a localized nodal mass in patients with Hodgkin disease( particularly nodular sclerosing ) Isolated enlargement of mediastinal or hilar nodes outside the anterior mediastinum should suggest an alternative diagnosis.