eMedicine Specialties > Radiology > Chest
Mediastinum, Germ Cell Tumors: Imaging
Updated: Jul 25, 2008
Radiography
Findings
Smooth, well-defined anterior mediastinal tumor with heterogeneous attenuation associated with calcific intratumoral nodules suggests a mediastinal teratodermoid. Note also the curvilinear calcification.
Coned view of the superior mediastinum shows a well-defined anterior mediastinal tumor with calcific intratumoral nodules suggestive of a mediastinal teratodermoid. Note also the curvilinear calcification
Smooth, well-defined anterior mediastinal tumor with uniform attenuation. At surgery, a mediastinal dermoid was diagnosed. Note the hilum-overlay sign, suggestive of an anterior or posterior mediastinal mass. See also Images 6-7 in Multimedia.
Lateral conventional tomogram in the same patient as in Image 4 shows a smooth, well-defined, uniformly attenuating anterior mediastinal mass with no calcification.
Lobulated but smooth and well-defined superior mediastinal mass with uniform attenuation. See also Image 9 in Multimedia.
Another patient with a biopsy proven anterior mediastinal dermoid extending across both sides of the midline.
Standard chest radiography is usually the first imaging procedure performed in an individual with symptoms referable to the thorax (see Images above and Images 1-2, 4, 8, 10, 13-15, 17-19 in Multimedia).
Most asymptomatic anterior mediastinal masses, particularly benign masses, are discovered incidentally on PA and lateral chest radiographs. The radiographs are often obtained for reasons unrelated to the germ cell tumor (GCT). The lateral chest radiograph is valuable in localizing the mass to the appropriate mediastinal compartment; it provides a clue as to what may be the pathology, and it limits the number of disorders in the differential diagnosis. This information, combined with the patient's age, sex, and associated clinical findings, aids the radiologist in the appropriate choice of further diagnostic techniques.
On chest radiographs, benign tumors appear as well-circumscribed, anterior mediastinal masses. Calcification can be seen in up to 26% of cases. Malignant lesions are less well defined than benign ones; they have fuzzy margins, and they may obliterate fat planes between the great vessels and the pericardium. The sternum may be eroded, and associated lung and bone lesions and mediastinal lymphadenopathy may be depicted. Calcification occurs in less than 1% of malignant anterior mediastinal masses.
Degree of Confidence
Despite major advances in cross-sectional imaging, the conventional chest radiograph retains a major role in the initial diagnosis of mediastinal masses. It guides the clinician in what to ask next in the investigation of the patient with a mediastinal mass. The radiograph may be reassuring when a well-defined asymptomatic anterior mediastinal mass with calcification is detected.
Standard chest radiography is universally available, noninvasive, and inexpensive; it also imparts a low dose of radiation, and the images are easy to interpret.
False Positives/Negatives
Differential diagnosis. Mediastinal widening in a child with acute lymphatic leukemia caused by mediastinal lymphadenopathy.
Differential diagnosis. Chest radiograph shows extensive mediastinal lymphadenopathy due to non-Hodgkin lymphoma.
Differential diagnosis. Posteroanterior chest radiograph shows a mass in continuation with the aortic knuckle. Findings on contrast-enhanced CT confirmed that the mass was an aortic aneurysm (not shown).
Differential diagnosis. Posteroanterior (top left) and lateral (top right) chest radiographs and CT scans in mediastinal (bottom left and middle) and bone window (bottom right) show an Askin tumour with bone destruction.
As with any other anatomic imaging study, the appearances of an anterior mediastinal mass are nonspecific, with a wide differential diagnosis. Differentiation between benign and malignant lesions may not be possible. CT is superior at depicting calcification and obliteration of fat planes, mediastinal lymphadenopathy, and bone erosions. Most patients with anterior mediastinal masses are further evaluated with cross-sectional imaging.
Computed Tomography
Findings
Contrast-enhanced axial CT scan shows an ill-defined anterior mediastinal mass with irregular borders that is infiltrating the mediastinal fat. CT-guided needle biopsy revealed a mediastinal seminoma.
Differential diagnosis. Contrast-enhanced CT through the anterior mediastinum shows a minimally enhancing anterior mediastinal mass. At surgery, a malignant thymoma was diagnosed.
Contrast-enhanced CT through the anterior mediastinum shows a minimally enhancing anterior mediastinal mass. At surgery, a malignant thymoma was diagnosed (see also Image 11 in Multimedia).
Contrast-enhanced CT scan obtained through the mediastinum in 56-year-old man shows an infiltrative enhancing tumor. Note the pleural effusion. Biopsy confirmed a sarcomatous-type germ cell tumor.
Posteroanterior chest radiograph and nonenhanced CT scans obtained through the mediastinum in 18-year-old man shows a large tumor involving the anterior, middle, and posterior mediastinum. Note the left pleural effusion. Biopsy confirmed a malignant teratoma.
Benign anterior mediastinal masses are typically depicted on CT as well-marginated, lobulated, encapsulated, mixed solid and cystic masses. The lesions typically extend to 1 side of the midline. In 13% of patients with an anterior mediastinal mass, the tumor extends into the middle and posterior mediastinal compartments. Cystic areas that are often multilocular and thinly septate are found in up to 88% of cases (see Images above and Images 4, 11-12, 16 in Multimedia).
Tumors are predominantly cystic in 80% of cases. About 50-73% of benign tumors have fat content, and 25-50% tumors are calcified. A fat-fluid layer may be found in up to 11% of patients; pleural effusion may be found in up to 17% of cases; and pericardial effusion may be found in 5%.
CT may useful in differentiating ruptured from unruptured mediastinal teratomas. Severe symptoms (chest pain or hemoptysis) are more common in patients with ruptured tumors (71%) than in patients with unruptured tumors. With ruptured mediastinal teratomas, the internal components are generally inhomogeneous, whereas with unruptured tumors, each internal compartment of the mass shows homogeneous attenuation. Other CT findings in ruptured tumors include fat-containing masses in adjacent lung parenchyma, consolidation or atelectasis in the adjacent lung, pericardial effusion, and pleural effusions.
Mature teratomas of the mediastinum typically appear on CT as heterogeneous anterior mediastinal masses containing areas of soft tissue, fluid, fat, or calcium attenuation, or any combination of these. Fluid-containing cystic areas, fat, and calcification occur frequently. Cystic lesions without fat or calcium are seen in 15% of tumors. Fat-fluid levels, considered highly specific for the diagnosis of mediastinal mature teratoma, are uncommon. CT is the imaging technique of choice in the evaluation of these lesions.
Malignant lesions are ill defined and have irregular borders, which infiltrate the mediastinal fat.21,22
Degree of Confidence
CT is the imaging modality of choice in the evaluation of mediastinal lesions. CT is an excellent modality for determining the exact location of the mediastinal tumor, as well as its relationship to adjacent structures. It also is useful in differentiating masses that originate in the mediastinum from those that encroach upon the mediastinum from the lung or other structures. CT scans may help in differentiating various tissue attenuations, and they are highly accurate in differentiating fluid, fat, calcification, and cysts from solid tumors. CT may be used to assess the degree of vascularity of mediastinal tumors.
CT scanning is better than other cross-sectional imaging studies in revealing evidence of local invasion of adjacent structures by a mass or the presence of intrathoracic metastases. Fat-fluid levels are considered highly specific for the diagnosis of mediastinal mature teratoma, but they are uncommon.
False Positives/Negatives
Although CT is highly sensitive in the diagnosis of anterior mediastinal masses, its specificity is low with regard to differentiating benign from malignant lesions and in classifying malignant lesions of various histologic types.
Magnetic Resonance Imaging
Findings
Continuing developments in MRI have resulted in improved image quality and decreased acquisition times. MRI is largely used as an adjunct to CT scanning in the evaluation of mediastinal tumors. In this setting, MRI provides additional information about the nature, location, and extent of disease.
MRI reveals masses of heterogeneous signal intensity, and it is more sensitive than CT in depicting infiltration of the adjacent structures by fat plane obliteration. It is performed as an ancillary study.
CT is more accurate than MRI in detecting mediastinal tumors, but MRI appears to be better than CT for evaluating spread through the capsule of the tumor, as well as infiltration of adjacent areas of mediastinal fat.
MRI is an accurate, noninvasive technique in the evaluation of superior vena cava syndrome and/or mediastinal and thoracic-inlet venous obstruction caused by mediastinal tumors.23
Degree of Confidence
The fact that MRI does not require ionizing radiation, as well as its multiplanar capability, makes MRI an excellent modality for both the initial diagnosis of a mediastinal mass and for follow-up evaluation after treatment. The vascular images provided are superior to CT scans and can better delineate the relationship of an identified mediastinal mass to adjacent intrathoracic vascular structures. MRI may be used to differentiate between a suspected mediastinal mass and a vascular abnormality, such as an aortic aneurysm.
MRI contrast agents may be used when iodinated contrast material is contraindicated. MRI provides increased detail of the subcarinal and aortopulmonary window areas, as well as of the inferior aspects of the mediastinum at the level of the diaphragm. MRI is preferred to CT scanning in the evaluation of invasion or extension of tumors, especially tumors closely associated with the heart. In addition, MRI is superior to CT for defining masses impinging upon the thoracic inlet or occurring at the thoracoabdominal level.
False Positives/Negatives
As with other cross-sectional imaging modalitites, MRI is nonspecific with regard to tissue diagnosis of anterior mediastinal masses.
Ultrasonography
Findings
Mediastinal sonogram obtained through the right parasternal area of an anterior intercostal space shows a mass of uniform echogenicity with posterior acoustic enhancement in the same patient as in Images 5-6 in Multimedia.
Mediastinal sonogram obtained through the suprasternal notch in the same patient as in Image 11 shows an ill-defined tumor with a heterogeneous echo pattern. At surgery, a teratodermoid was diagnosed. The mass contained small foci of calcification.
Patient with asymmetrically placed anterior mediastinal mass. Lateral linear tomogram shows a well-defined, uniformly attenuating mass (not shown), sonogram shows a mass with smooth, uniform echotexture. The patient had not undergone surgery, and findings on follow-up over several years showed little change.
Ultrasonography has traditionally been used to differentiate solid from cystic masses in places other than the mediastinum; its role has been extended, and it is now used to differentiate such masses in the anterior mediastinum. Sonograms may assist in determining a connection between a mass and adjacent structures. These studies are more useful in the evaluation of masses associated with the heart, as well as in vascular abnormalities (see Images above and Images 7, 9 in Multimedia).
In general, given the accuracy and detail provided by CT scanning, MRI, and selected radionuclide scans, sonographic techniques are generally not used as primary tools in the evaluation of mediastinal tumors and cysts.24
Degree of Confidence
In addition to determining the size and topographic characteristics of mediastinal masses, sonography precisely depicts the internal structure of the tumor; sonographic findings may suggest a specific diagnosis when considered in light of the clinical presentation and the location of the tumor.
False Positives/Negatives
Ultrasonography remains operator dependent, and the anterior mediastinum may not be accessible because of the thoracic bony cage. As with other cross-sectional imaging modalities, tissue diagnosis may not be possible because the differential diagnosis of solid, cystic, and complex mediastinal masses is extensive.
Nuclear Imaging
Findings
Radioiodine scans are particularly useful in identifying anterior mediastinal masses at the level of the thoracic inlet, such as the substernal extension of cervical thyroid goiter. Because germ cell tumors and thyroid abnormalities may both appear as anterior mediastinal masses, radioiodine scans may help to confirm or eliminate the involvement of thyroid tissue.
Indium-111 octreotide and pentetreotide scans may help in differentiating germ cell tumors from mediastinal carcinoids. Like other neuroendocrine tumors, carcinoids have somatostatin receptors and can therefore be imaged with somatostatin analogues (octreotide, pentetreotide) tagged to an appropriate radioisotope. Single-photon emission CT (SPECT) and subtraction techniques improve detection.
Sarcoid anterior mediastinal lymphadenopathy may be differentiated from GCT by use of radionuclide scanning. Gallium-67–avid sarcoid disease has been reported in more than 90% of cases of pulmonary involvement.
Positron-emission tomography (PET) has been studied extensively for use in the evaluation of a number of neoplasms, such as lung cancers, colorectal cancers, breast cancers, lymphomas, and melanomas. Its use in the evaluation of mediastinal tumors is under investigation.
Degree of Confidence
Through advances in physiologic imaging of mediastinal lymph nodes with fluorodeoxyglucose (FDG) positron-emission tomography (PET) imaging, this modality now provides better diagnostic accuracy than that obtained with anatomic CT scanning or MRI.
At present, an imaging strategy that uses both FDG-PET and CT scanning appears to be the most accurate, noninvasive, and cost-effective means of assessing nodal status in patients with non – small cell lung cancer. The use of FDG-PET in the imaging and staging of germ cell tumors has not yet been investigated.25,26
False Positives/Negatives
The uptake of technetium-99m pertechnetate and radioiodine is not specific for thyroid tissue, and uptake may occur in ectopic gastric mucosa in duplication cysts and Barrett's esophagus. Gallium-67 uptake may occur in neoplastic, inflammatory, and infective foci. The results of FDG-PET are also nonspecific, and findings must be correlated with clinical presentation and other imaging findings.
Angiography
Findings
Conventional angiography has been used to differentiate mediastinal masses from vascular abnormalities and to demonstrate the relationship between known masses and adjacent vascular structures. MRI and magnetic resonance arteriography (MRA) appear to satisfactorily define masses in this area.
Degree of Confidence
Angiography is invasive, but it is still regarded as the criterion standard in imaging the heart and major blood vessels. However, MRA and CT angiography are increasingly being used in these roles.
False Positives/Negatives
False-negative results may occur in cases involving aneurysms that are associated with laminar intraluminal thrombus. The sensitivity and specificity of angiography in the diagnosis of aortic aneurysms are 85% and 95%, respectively.
More on Mediastinum, Germ Cell Tumors |
| Overview: Mediastinum, Germ Cell Tumors |
 Imaging: Mediastinum, Germ Cell Tumors |
| Follow-up: Mediastinum, Germ Cell Tumors |
| Multimedia: Mediastinum, Germ Cell Tumors |
| References |
| Further Reading |
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Keywords
germ cell tumors, germ cell neoplasm, mediastinal germ cell tumor, GCTs, Klinefelter syndrome, teratoma, seminoma, epidermoid cyst, dermoids, dermoid cyst, mediastinal dermoid
