Approach to Mediastinal Masses
- Clinical Presentation:33% of all masses present in patients less than 15 years oldIf small, usually asymptomatic and found incidentally (cautious work up)If large, usually present with respiratory distress (frantic work up)
-The anterior mediastinal compartment is bordered by the sternum anteriorly, and the ventral cardiac surface posteriorly.
-This compartment contains fat, ascending aorta, lymph nodes, internal mammary artery and vein, adjacent osseous structures (ribs and sternum), thymus.
-Therefore will most likely see masses typical to these structures, ie a lymphoma in lymph nodes.
It is located above a horizontal line drawn from the angle of Louis posteriorly to the spine.
Structures in the superior mediastinal compartment include the thyroid gland, aortic arch and great vessels, proximal portions of the vagus and recurrent laryngeal nerves, esophagus and trachea.
The borders are composed of the anterior mediastinal compartment ventrally, and the anterior surface of the spine, posteriorly.
Structures in the middle mediastinal compartment include the esophagus (which will not be visible unless there is a problem), vagus nerve, recurrent laryngeal nerve, heart, proximal pulmonary arteries and veins (hilar), trachea and root of the bronchial tree, and superior and inferior vena cava
The posterior mediastinum borders the anterior surface of the spine posteriorly to the ribs.
Structures in the posterior mediastinal compartment include the descending aorta, adjacent osseous structures (the spine and ribs) and nerves, roots, spinal cord, and the azygous and hemiazygous veins.
Anterior Mediastinal Masses: (4 T's) (30% of mediastinal masses)
- Thyroid (Ectopic)
- (Terrible) Lymphoma
Middle Mediastinal Masses (A + B) (30% of mediastinal masses)
- Adenopathy (infection [bacterial, granulomatous], neoplasm [leukemia / lymphoma, metastases])
- Bronchopulmonary foregut malformations (Esophageal duplication cyst, bronchogenic cyst, sequestration)
Posterior Mediastinal Masses: (N) (40% of mediastinal masses)
- Sympathetic ganglion tumors: neuroblastoma, ganglioneuroblastoma, ganglioneuroma (95% of posterior mediastinal masses)
- Neurenteric cyst
- Extramedullary hematopoesis
- Paravertebral soft tissue mass from infection
- PA and lateral chest films are the first step in distinguishing from which mediastinal compartment the mass is arising from.
- Computed tomography or magnetic resonance imaging is the next step, better characterizing the nature and extent of the lesion, thus narrowing the differential diagnosis. MRI is especially good at looking for spinal canal invasion in posterior mediastinal masses
- Tissue biopsy is required for definitive diagnosis, and surgical resection for definitive cure.
Case 37 - Eight year old male with a heart murmur
PA and lateral chest films show a large anterior mediastinal mass causing narrowing and rightward deviation of the trachea. The mass is not calcified.
CT exam show a low density mass in the anterior mediastinum with irregular walls with calcium in it.
Dx Teratoma, Anterior Mediastinal
Three year old male with an incidentally noted chest mass
single slice from an enhanced chest CT exam shows the mass to be non-enhancing, posterior to the right bronchi, and next to the esophagus.
Dx: Esophageal Duplication
Eighteen year old female with an incidentally noted chest mass
Esophageal duplication cyst
Eleven year old male with upper respiratory symptoms and wheezing.
Slice from an enhanced chest CT exam shows a multi-loculated non enhancing mass in the anterior mediastinum
Five year old male with cough and fever
Soft tissue in the anterior mediastinum compatible in appearance with thymus
Twelve year old female with a chest mass
PA and lateral chest films show a large, lobulated anterior mediastinal mass displacing the trachea to the right.
A chest CT exam shows the mass to extend from the neck to the diaphragm, compressing the tracheal and left mainstem bronchus leading to left lower lobe atelectasis. The chest wall mass is partially eroding the sternum and there is periosteal reaction. Axillary adenopathy is present also.
Dx:Lymphoma, Hodgkin, Anterior Mediastinal, Sternal Involvement
PA and lateral chest films show a mediastinal mass that had enlarged in the 4 year interval that may be spreading the right 5th and 6th ribs apart.
An enhanced chest CT exam shows a homogeneous mass, of fatty density, with a few septations, in the right posterior mediastinum causing some anterior displacement of the right mainstem bronchus.
Dx:Lipoma, Posterior Mediastinal
PA and lateral chest films show an anterior mediastinal mass and a large right pleural effusion.
Two contiguous slices from an enhanced chest CT exam show a homogenous, solid, anterior mediastinal mass and a large right pleural effusion.
Dx-Lymphoma, Non-Hodgkin, Anterior Mediastinal
PA and lateral chest films show a soft tissue mass in the right posterior costophrenic sulcus.
Final Diagnosis:Intrathoracic Kidney
PA and lateral chest films from the day of admission demonstrate a large round opacity in the left lower lobe that abuts the diaphragm
Two coronal T1 weighted images and one axial T2 weighted image from an MRI exam from the 5th hospital day demonstrate a posterior mediastinal mass that extends into the retrocrural regions of the chest bilaterally and that enhances uniformly. There is no evidence of metastatic disease.
large mass in the posterior mediastinum on the left.
Bone window images from a chest CT exam from the day of diagnosis demonstrate a large spherical calcified left paravertebral mass measuring 12 x 11 x 8 cm in size. There is a pleural effusion and a shift of mediastinal structures to the right. The mass appears to extend via the retrocrural space into the abdomen causing displacement of the left kidney and inferior vena cava. The mass crosses the midline. Some minimal thoracic vertebral body remodeling and rib thinning is seen on the left. No spinal canal invasion or liver metastases are seen
MRI exam performed 3 weeks after diagnosis. Coronal and sagittal T1 weighted images without contrast, and coronal and axial T2 weighted MRI images could not definitely identify the left adrenal gland, and therefore suggested it could be the origin of the midline mass. There was evidence of tumor invasion into several neural foramina and the spinal canal.
- . Almost all of them originate in the anterior mediastinum within or in close contact with the thymus. There is a variety of benign and malignant germ cell neoplasms. The majority of germ cell neoplasms (60–70%) are benign including mostly mediastinal teratoma and dermoid cysts that occur with equal frequency in males and females.
- On CT scans, the tumour is heterogeneous and limited with well-defined margins. Dermoid cysts and teratomas contain areas of different densities including fat, soft tissue and cystic
- Fatty and cystic components are present in about half of the cases. Occasionally a fat–fluid level may be present and is highly suggestive of the diagnosis. Curvilinear, spherical or irregular calcifications within the mass may be seen Identification of a tooth, while rare, is diagnostic.
Germ Cell Tumors
- Malignant germ-cell neoplasms have a male predominance. They include mediastinal seminoma, mediastinal choriocarcinoma, embryonal cell carcinoma, yolk sac tumour and teratocarcinomas
- On the radiograph, the mass is similar to benign germ cell neoplasm excepted that the mass itself is often lobular in outline. Metastases may be seen in the lung, pleura or bone. CT or MR features of the tumour are similar to other primary malignant tumours arising within the anterior mediastinum
- The mass is lobular and asymmetrical. The margins may be well-defined or irregular. The adjacent mediastinal fat planes may be obliterated, although this is not a feature of definite invasion. The tumour may appear as either a homogeneous soft tissue mass or a heterogeneous mass containing areas of contrast enhancement interspersed with areas of decreased attenuation due to necrosis or haemorrhage
- Calcifications are uncommon.
- Mediastinal lymphadenopathy may be present
- primary malignant neoplasm of the lymphoreticular system, particularly of the lymphocytes and histiocytes and the derivatives of these two cell types, surrounded by non-neoplastic inflammatory cells. Lymphomas include Hodgkins disease and non Hodgkins lymphoma. Both frequently involve the chest.
- neoplasm arising from thymic epithelium. It is the most common cause of a thymic mass. It presents as an anterior mediastinal mass.
- Thymomas occur usually between the ages of 40 and 60 years old, in males or females equally. They are very unusual in patients under the age of 20. Thymomas generally occur as incidental findings discovered on a chest radiograph in otherwise healthy individuals. They may also occur in association with other abnormalities such as myasthenia gravis, red cell aplasia and hypogammaglobulinaemia. Myasthenia gravis, the most frequent association of the three, is present in roughly 50% of patients with thymoma. Approximately 15% of patients with myasthenia gravis have a thymoma
- On the chest radiograph, thymomas are depicted as a round or lobulated mass located in the anterior mediastinum
- . On lateral films, they often appear as a well-defined mass in the normally clear restrosternal space.
- Sometimes, the tumour is situated more inferiorly adjacent to the left or right borders of the heart and occasionally as low as the cardiophrenic angle.
- Occasionally the tumour is too small (1 cm) to be depicted on the chest radiograph, and is only detected on CT scans Punctuate or curvilinear calcifications may be seen in both benign or invasive thymomas.
- On CT scans, benign thymomas appear as a round or oval mass located in the prevascular space of the mediastinum, or at any level from the thoracic inlet to the diaphragm within the anterior mediastinum. Intratumoral calcifications are present in 20 – 30% of the cases and areas of cystic degeneration are common
- Invasive thymomas typically appear as irregular masses growing along pleural surfaces.
- may be congenital or acquired.
- On plain radiographs, thymic cysts are indistinguishable from other nonlobulated thymic masses, notably thymomas
- CT scans show a well-defined cystic mass demonstrating CT attenuation values typically consistent with fluid. The appearance, however, may vary if haemorrhage or infection complicate the cyst. Curvilinear calcification of the cyst wall may occur in a few cases.
Thyroid mass, mediastinal,
- usually a colloid or adenomatous goitre, and occasionally a carcinoma.
- The great majority of mediastinal thyroid masses represent a downward extension of a thyroid mass that originates in the neck. They may extend into the anterior, middle and posterior compartments of the mediastinum. When located in the anterior mediastinum, thyroid masses are almost always located posterior to the great vessels, most often in a paratracheal location. A true primary ectopic mediastinal goitre is very rare. Most patients are asymptomatic; symptoms, however, may arise from compression of the trachea and oesophagus.
- On chest radiographs, intrathoracic thyroid masses have a well-defined spherical or lobular outline. They may displace and narrow the trachea. Posteriorly placed thyroid masses separate normal trachea and the oesophagus. Occasionally they may compress the brachiocephalic veins and cause superior vena cava obstruction. On CT scans the mediastinal mass due to thyroid goitre typically contains:
- - foci of high attenuation on enhanced scans reflecting the high iodine content of thyroid tissue;
- - foci of calcifications (usually dense and well defined, with a nodular, curvilinear or circular configuration); and
- - intense and prolonged enhancement following intravenous contrast The key feature for the diagnosis is demonstration of continuity of the mass with the cervical thyroid gland. This is easily obtained by helical CT scan over the lower neck and chest. Chest MR may also be used. Radioiodine scan may also onfirm the diagnosis by demonstration of radioiodine uptake from foci of functional thyroid tissue within the mass. Distinction between benign and malignant goitre by imaging is not possible unless the tumour clearly invades the adjacent structures.
- On the chest radiograph, bronchogenic cysts typically appear as smooth, sharply marginated mediastinal masses. On CT scans they appear as round or oval homogeneous masses with well-defined margins with barely or no perceptible walls. They have a certain plasticity and mould around normal anatomical structures (Fig.1). Half of them show an attenuation similar to that of water and the remainder appear of soft tissue attenuation. Occasionally they show a very high attenuation related to a milk of calcium content. Curvilinear calcification of the wall is very rare. Absence of enhancement after administration of iodinated contrast medium is the rule.
- On MR scans, bronchogenic cysts frequently show a signal intensity higher than that of muscle on T1-weighted images due to their high proteinaceous content (Fig. 1b). Uncommonly a fluid–fluid level may be present. The signal intensity on T2-weighted images is very high suggesting a cystic lesion (Fig. 1c). The absence of enhancement after intravenous injection of gadolinium allows differentiation of the cysts from solid tumours
- Chest radiograph
- On the chest radiograph, the ease with which lymph node enlargement can be recognized depends on the particular location (see lymph node classification chest). Enlargement of the right upper paratracheal nodes causes uniform or lobular widening of the right paratracheal stripe, and an increase in density of the superior vena cava of which the border may become convex to the lung. The enlarged right lower paratracheal nodes push the azygos vein laterally increasing the diameter of the combined opacities of both node and azygos arch
- The aortopulmonary nodes may cause a bulge in the angle between the aortic arch and the main pulmonary artery. If they are substantially enlarged, the left upper paratracheal nodes induce mediastinal widening.
- The radiographic features of subcarinal node enlargement include the displacement of the azygo-oesophageal line that becomes convex to the lung, an increased opacity of the subcarinal space on the posteroanterior film and a lack of visibility of the external surface of the medial wall of the intermediate bronchus.
- Enlargement of the anterior mediastinal nodes may be substantial to be visible on the chest films. In such case, mediastinal widening is frequently bilateral and lobulated in outline. Increased opacity of the retrosternal area on the lateral view may be sometimes the early sign.
- Enlarged paraoesophageal and posterior mediastinal nodes produce displacement of the azygo-oesophageal and paraspinal lines. The radiographic signs of enlargement of hilar lymph nodes are hilar enlargement, lobulation of outline or rounded mass in a portion of the hilum
- Lymph node enlargement is defined on the basis of a short-axis node diameter exceeding 1 cm. The assessment of lymph node size, however, has a limited accuracy in determining whether hilar and mediastinal lymph nodes are normal or abnormal (lung cancer staging). The larger the node, the more likely it indicates a significant abnormality. Lymph nodes having a short axis of 2 cm or more, often reflect the presence of neoplasm, sarcoidosis or infection and should always be regarded as potentially significant. In the absence of a known disease an enlarged node less than 2 cm in short axis diameter should be regarded as likely to be hyperplastic or postinflammatory. Three CT patterns may be identified:
- discrete enlarged nodes that remain well defined;
- coalescence of enlarged nodes, involving surrounding mediastinal fat and forming a single larger mass with poor margins that can indicate extension of the disease process through the node capsule; and
- diffuse mediastinal involvement characterized by infiltration of mediastinal connective tissue and fat with no recognizable nodes or node masses. The first pattern may be seen in association with all causes of lymphadenopathy whereas coalescence of enlarged nodes suggests infections, granulomatous disease and neoplasm. Diffuse mediastinal involvement is more typical of lymphoma, large cell undifferentiated carcinoma and acute or chronic mediastinitis. CT can also be used to define the density of lymph nodes. Enlarged nodes may be calcified (see calcification mediastinal lymph node), or low in density and necrotic in appearance or can enhance following intravenous injection of contrast media. Low attenuation lymph nodes after administration of contrast media, with or without rim enhancement typically reflect the presence of necrosis
- The majority of them are located in the right anterior cardiophrenic angle although they may occur anywhere in the pericardium, posterior cardiophrenic angle or superior retroaortic pericardial recess.
- On chest radiographs, they appear as well defined round or oval masses in contact with the heart
- Calcification is exceptional.
- On CT, they appear as smooth well-defined masses without any perceptible wall. They typically demonstrate fluid attenuation that may be close to water or, because of viscous fluid, may be in the soft tissue range
- Similarly the MR signal characteristics are typically that of water (low signal intensity on T1-weighted images, and bright signal on T2- weighted images) (Fig. 1c, d). but may vary depending on the cyst content. The pericardial cyst may be of almost any size.
- rare marrow expansion associated with severe anaemia, notably thalassaemia and sickle cell disease.
- It is a rare cause of masslike collections within the chest. The masses are usually asymptomatic.
- Radiologically they present typically as longitudinal, bilateral, lobulated paraspinal masses
- On CT scans the appearance is that of homogeneous mass of soft tissue or slightly higher density structure
Neuroenteric cyst, mediastinal,
- The vertebral anomalies including hemivertebrae, butterfly vertebra or spina bifida may be located at the level of the cyst.
- The cyst may be connected to the meninges through a midline defect in one or more vertebral bodies.
- Radiographically, neuroenteric cysts are round, oval or lobulated well-defined homogeneous cystic masses located in the posterior mediastinum or paravertebral area.
- Their communication with the subarachnoid spaces may be demonstrated on MR scans, which have replaced CT myelography.
- Roughly 70% of neurogenic tumours arising in the chest are benign. Usually, they occur in younger patients, in the first four decades of life. Males and females are equally affected.
- On chest radiography, neurogenic neoplasms are seen as a sharply circumscribed homogeneous mass (Fig.1). Rib erosion with a sclerotic border is suggestive of a benign lesion. The presence of frank bone destruction or spread to multiple ribs is suggestive of malignancy. Calcification may be present in all types of neurogenic neoplasm
- On CT scans, neurogenic neoplasms typically appear as homogeneous soft tissue density although many of them have a low attenuation attributed to the lipid elements in the nerve sheaths or cystic degeneration. Due to their vascularization, they enhance after the administration of intravenous contrast medium.
homogeneous mass abutting the right border of the heart which corresponds to a schwannoma of the right phrenic nerve.
- CT is recommended as the primary imaging modality for assessing masses localized within the anterior and middle compartments of the mediastinum. It provides information on the precise location of the mass and its relationship to adjacent structures. It can determine whether the mass is cystic or solid, and whether it contains calcium or fat.
- Contrast enhancement provides information concerning the vascularization of the mass and its relationship with adjacent structures.
- Radioiodine scan is required if thyroid goitre is suspected.
- MRI is superior to contrast enhanced CT, however, in assessing the relationships of the mass to vascular structures and in determining vascular invasion.
- For masses localized in the posterior compartment of the mediastinum, MRI is preferentially used because of its superior ability in assessing the relationship of the mass to the adjacent spine. In case of suspicion of oesophageal abnormality, a barium swallow is indicated.