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Mediastinal MassMediastinal Mass

ANATOMY

The mediastinum is a narrow, vertically oriented structure that resides between the medial parietal pleural layers of the lungs.

Mediastinal Divisionssuperior anteriormiddle posterior

The superior mediastinum :The space between the thoracic inlet and the superior aspect of the aortic arch All mediastinal structures above animaginary line drawn between the sternal angle and the fourth thoracic intervertebral disk on the lateral chest radiograph

The anterior mediastinum is the space anterior to the heartand great vessels on the lateral chest radiograph. It is borderedanteriorly 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 spaces

Posterior mediastinum : Descending aorta Esophagus Azygos and hemiazygos veins Thoracic duct Sympathetic ganglia and intercostal nerves Lymph nodes

Localize to the mediastinum

The following characteristics indicate that a lesion originates The following characteristics indicate that a lesion originates within the mediastinumwithin the mediastinum : :

Unlike lung lesions, a mediastinal mass Unlike lung lesions, a mediastinal mass will not will not contain air contain air bronchogramsbronchograms . .

The margins with the lung will be The margins with the lung will be obtuseobtuse . . Mediastinal lines (azygoesophageal recess, anterior and Mediastinal lines (azygoesophageal recess, anterior and

posterior junction lines) will be posterior junction lines) will be disrupteddisrupted . . There can be associated There can be associated spinal,spinal, costal costal or or sternal sternal

abnormalitiesabnormalities..

LEFTLEFT: A lung mass abutts the mediastinal surface and creates : A lung mass abutts the mediastinal surface and creates acute angles with the lung.acute angles with the lung.RIGHTRIGHT: A mediastinal mass will sit under the surface of the : A mediastinal mass will sit under the surface of the mediastinum, creating obtuse angles with the lungmediastinum, creating obtuse angles with the lung..

On the x-ray on the left there is a lesion that has an On the x-ray on the left there is a lesion that has an acute border with the mediastinum. acute border with the mediastinum. This must be a lung mass (This must be a lung mass (pancoast tumorpancoast tumor))The chest radiograph on the right shows a lesion with an The chest radiograph on the right shows a lesion with an obtuse angle to the mediastinum. obtuse angle to the mediastinum. This must be a mediastinal mass(This must be a mediastinal mass( thymomathymoma ) )..

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 Distinction of tumor from fibrosis PET>MR>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 false-negative 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

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.

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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 difficulttwo conditions can coexist

Differentioal diagnose; cystic degeneration of a thymoma lymphoma germcell neoplasm lymphangioma

The CT shows an anterior mediastinal mass with water The CT shows an anterior mediastinal mass with water density attenuation.density attenuation.

This is typical for aThis is typical for a thymic cyst thymic cyst..

Thymic CarcinoidNeuroendocrine 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 chest wall involvement should suggest the diagnosis.

LymphomaMost 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.