Mediastinal fluid collection

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Approach to Imaging of Mediastinal Conditions in the Adult

Diseases of the Chest, Breast, Heart and Vessels 2019-2022 pp 27-35 | Cite as

  • Sanjeev BhallaEmail author
  • Edith Marom

Open Access

Chapter

First Online:

Part of the IDKD Springer Series book series (IDKD)

Abstract

Generating a relevant different diagnosis for mediastinal processes rests on the principles of localization and characterization.

Once a process or mass can be localized to the mediastinum, it should be localized within the mediastinum. Many of us use an approach first championed by Ben Felson. Using a lateral radiograph or sagittal CT or MR, a line is drawn from the anterior tracheal wall to the posterior inferior vena cava. This line separates the anterior mediastinum from the middle mediastinum. A second line is drawn 1 cm posterior to the anterior margin of the vertebral body. This line separates the middle from the posterior mediastinum. This approach can be useful in creating concise, meaningful differential diagnoses.

After localization, CT or MR should be performed for lesion characterization. Knowing whether a lesion has a significant vascular, fluid or fat component can be very helpful in suggesting a more specific diagnosis.

Keywords

CT MR Mediastinum ITMIG (International Thymic Malignancy Interest Group) Anterior mediastinum Middle mediastinum Posterior mediastinum 

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Learning Objectives

  • To understand an approach to the adult mediastinum based on localization of lesions within the mediastinum and attenuation/intensity features on cross-sectional imaging.

  • To highlight conditions that disregard the compartmental model.

  • To use some cases to show the additional value of MR in evaluating the adult mediastinum.

3.1 Introduction

The mediastinum is an anatomic space defined by the thoracic inlet superiorly and the diaphragm inferiorly. It extends from the sternum to the vertebral bodies. Yet, despite its landmarks, there are no structures that completely separate the mediastinum from the neck above or the retroperitoneum below. Imaging of the mediastinum and generating a relevant different diagnosis rest on the principles of localization and characterization.

Once a process or mass can be localized to the mediastinum, it should be localized within the mediastinum. Many of us use an approach first championed by Ben Felson. Using a lateral radiograph or sagittal CT or MR, a line is drawn from the anterior tracheal wall to the posterior inferior vena cava. This line separates the anterior mediastinum from the middle mediastinum. A second line is drawn 1 cm posterior to the anterior margin of the vertebral body. This line separates the middle from the posterior mediastinum. No anatomic structures actually divide the mediastinal compartments, but this approach can be useful in creating concise, meaningful differential diagnoses. Keep in mind certain processes may involve more than one compartment and that a large mass may be hard to localize.

More recently, the International Thymic Malignancy Interest Group (ITMIG) has proposed a modification of lesion localization based on MDCT. In this model, three compartments are used: prevascular, visceral, and paravertebral. The main difference from the modified Felson technique is the inclusion of the heart and aorta in the visceral compartment (middle compartment) (Fig. 3.1).

After localization, cross-sectional imaging (either CT or MR) should be performed for lesion characterization. Knowing whether a lesion has a significant vascular, fluid or fat component can be very helpful in suggesting a more specific diagnosis. PET/CT is used mainly to evaluate lymph node metastases in lung cancer. It is used as well in the evaluation of solid mediastinal masses.

This approach of localization and characterization will provide the interpreting radiologist a solid foundation in imaging the mediastinum.

3.2 Anterior Mediastinum/Prevascular Compartment

Most anterior or prevascular mediastinal masses are thymic in origin. Even lymphomas and germ cell tumors tend to arise in cells within the thymus. A useful differential list should be based on age, as germ cell tumors are almost unheard of in patients older than 45 years. Most anterior mediastinal masses tend to be lymphomas, germ cell tumors, or thymomas. Many texts will include thyroid goiter in the list for anterior mediastinal lesions. We, however, have found that most goiters tend to extend into the middle mediastinum or visceral compartment (Fig. 3.2).
Observing fluid attenuation or intensity can be very helpful in approaching anterior mediastinal masses. Pure cystic lesions are benign (usually thymic or pericardial cysts). Separating pericardial from thymic cysts is based on location as thymic cysts tend to be spade-shaped and reside in the thymic bed, while pericardial cysts tend to be rounder and are more commonly found in the right cardiophrenic angle (Fig. 3.3). As the amount of soft tissue within the lesion increases, one should consider the increased likelihood of a malignancy. Both lymphoma and cystic thymoma will tend to have soft tissue elements that will enhance on MR or CT (Fig. 3.4). Germ cell tumors also follow this rule. The classic teaching is that the germ cell tumor should be fat in attenuation. Many teratomas do contain some fat elements, but almost all are cystic (Fig. 3.5). As with the other lesions, if the soft tissue elements dominate, then a malignant germ cell tumor should be favored, such as seminoma. Interestingly, malignant germ cell tumors are quite rare in female patients.

The visualization of fat intensity or attenuation can also be very helpful. In the anterior or prevascular mediastinum, most fatty masses are benign. As described above, an anterior mediastinal mass with fat and fluid suggests a teratoma (benign germ cell tumor) (Fig. 3.5). If the mass is purely fat, it may be the very rare thymolipoma but more likely will be a fat pad or anterior hernia (Morgagni hernia). Coronal or sagittal images are quite helpful in depicting vessels originating below the diaphragm. Visualization of these are key in separating hernias from fat pads or fatty tumors. In our practices, infarction of a pericardial fat pad or fat within the Morgagni hernia may present with chest pain. In the era of the frequent use of CT in the evaluation of chest pain, these areas of fat necrosis can simulate a neoplasm. Awareness of this potential pitfall will allow the patients to be treated appropriately.

Calcification can also be helpful. The incidence of calcification in thymomas varies from 10 to 40% (Fig. 3.6). Circular peripheral calcification may occur in solid thymomas. Teratomas contain calcium in about 35% of cases. Untreated lymphomas do not calcify and about 5% of them show calcifications after radiation therapy. Peripheral circular calcification can be a finding of an aneurysm. In this location, many such aneurysms represent bypass graft aneurysms. The presence of mediastinal wires should be a clue to this potential diagnosis.

Vascular or hyperenhancing lesions may present within the anterior or prevascular mediastinum. Often, these are related to the heart, ascending aorta. Rarely, ectopic parathyroid adenomas may present as vigorously enhancing anterior prevascular masses.

Key Point

  • Most anterior mediastinal masses are of thymic origin. Patient age and attenuation characteristics are key in narrowing the differential diagnosis. MR can be helpful in characterizing cystic lesions and in diagnosing thymic hyperplasia.

3.3 Middle Mediastinum/Visceral Compartment

Most middle mediastinal or visceral compartment masses represent lymphadenopathy, foregut duplication cysts, vascular lesion, or esophageal processes. They usually present with right paratracheal widening on a frontal chest radiograph or occasionally the doughnut sign on a lateral examination. As with the anterior mediastinal conditions, assessment of attenuation or intensity can be helpful. In the ITMIG model, the heart is included in this compartment. In our experience, left ventricular and left atrial conditions may occasionally simulate middle mediastinal, visceral masses.

If the mass is fluid in characteristic, the middle mediastinal mass most likely represents a foregut duplication cyst (either bronchogenic or esophageal). These cysts occasionally are higher in attenuation as a result of infection (Fig. 3.7) or hemorrhage and may even contain a fluid-calcium level from milk of calcium. The risk of malignancy in these conditions tends to almost nonexistent. As with anterior mediastinal lesions, the ratio of soft tissue to fluid needs to be considered. A foregut duplication cyst should have no soft tissue, enhancing element. If soft tissue is encountered, one must consider a potentially more significant process, usually low-attenuating lymphadenopathy. Such low-attenuating lymph nodes may be encountered in lung cancer, mucinous neoplasms, and mycobacterial disease (Fig. 3.8). In the superior mediastinum, papillary thyroid carcinoma can rarely mimic a foregut duplication cyst.

Unlike the anterior mediastinum or visceral compartment, fat cannot be considered benign. Although esophageal or tracheal lipomas and esophageal fibrovascular polyps contain fat, so may mediastinal liposarcomas. Although rare, these lesions may insinuate through the mediastinum and often have a predilection for the middle mediastinum.

Hypervascular lesions in the middle mediastinum or visceral compartment are most often hypervascular lymph nodes, or an intrathoracic extension of a goiter. Rarely a paraganglioma may present in this space. Interestingly, many of these lesions tend to abut the left atrium. The hypervascular lymph nodes (defined as higher in attenuation than skeletal muscle) may be seen with melanoma, plasmacytoma, Castleman’s disease, Kaposi sarcoma, and thyroid and renal cell cancer (Fig. 3.9). When the high attenuating structure is tubular, a vessel must be considered. Aortic arch anomalies and azygous vein enlargement often present as a middle mediastinal mass on radiography. Azygous vein variants tend to enlarge on portable radiographs (when the patient is supine) compared with upright radiographs.

Most mediastinal lymphadenopathy will present in the middle mediastinum or visceral compartment. Occasionally, these nodes will be calcified. Most often these calcified nodes are indicative of an old granulomatous process such as healed tuberculosis or histoplasmosis or sarcoidosis, but care must be taken to remember that certain tumors also tend to present with calcified mediastinal lymph nodes, including ovarian serous adenocarcinomas, mucinous colon neoplasms, and osteosarcomas.

Another potential for a perceived middle mediastinal mass on radiography will be a dilated esophagus. Although a distal mass may also result in esophageal dilatation, it is usually only achalasia that results in esophageal widening that can be seen on a chest radiograph.

Key Point

  • Most middle mediastinal masses will consist of lymphadenopathy, duplication cysts, vascular lesions, or esophageal masses. Attenuation characteristics of the lymphadenopathy compared to skeletal muscle can be helpful at honing in on the correct diagnosis.

3.4 Posterior Mediastinum/Paravertebral Compartment

A vast majority of posterior mediastinal or paravertebral masses will be neurogenic in origin (Fig. 3.10). In adults, these tend to be benign nerve sheath tumors, usually schwannomas and neurofibromas. In kids and younger adults, these tend to be sympathetic ganglion in origin, such as ganglioneuroblastoma, neuroblastoma, or ganglioneuroma. The key in separating the two groups is to assess the overall shape, comparing Z-axis to the XY-axis. The nerve sheath tumors tend to be spherical (equal in all three axes), while the ganglion lesions are longer in the Z-axis and are more cylindrical (akin to a sausage). Osseous lesions represent the second most common group of posterior mediastinal disease. Although metastases are often considered, one cannot forget about diskitis/osteomyelitis. This latter condition can present with insidious back pain and can easily be overlooked.

As with the other compartments, attenuation or intensity can be helpful. On CT, a potential pitfall is that myelin-rich neurogenic lesions may look cystic. For this reason, we often rely on MR with posterior mediastinal/paravertebral lesions. True posterior mediastinal cystic lesions are rare. Although neuroenteric cysts exist, they are often associated with vertebral anomalies and rarely encountered de novo in adults. Instead, a cystic lesion in the posterior mediastinum is much more likely to represent a lateral meningocoele or post-traumatic nerve root avulsion.

Fatty lesions are unusual in the posterior mediastinum but when encountered may invoke extramedullary hematopoiesis. Although rare, in patients with anemia, extramedullary hematopoiesis may develop in this space. The etiology of this condition remains unknown. Some authors have postulated that it develops from extruded marrow, while others have suggested that it develops from totipotent cells in the paravertebral space. When the patient is anemic, extramedullary hematopoiesis will present with bilateral masses that enhance similar to the spleen without a connecting bridge. As the patient returns to normal hematocrit, the yellow marrow will take over. The net effect is bilateral posterior mediastinal fatty masses. In the elderly, Bochladek hernias should be included in the differential diagnosis. Often the diaphragmatic defect can be seen.

Hypervascular lesions in in the posterior mediastinum or paravertebral space are less helpful than with the other compartments. Most often these are related to an aneurysmal aorta or enlarged collateral vessels as with aortic coarctation. As described above, extramedullary hematopoiesis may be seen with bilateral hypervascular paravertebral masses.

Key Point

  • Most posterior mediastinal masses are neurogenic in origin. Osseous lesions, however, should not be forgotten. Mutiplanar reconstructions and MR are particularly helpful in this compartment.

3.5 Conditions that Disregard the Compartment Model

Certain conditions tend to disregard the compartment model of the mediastinum. Even with these lesions understanding the attenuation or intensity can be helpful. These include infection and hematoma, which will result in fat stranding and soft tissue attenuation throughout the mediastinum, often in more than one compartment.

Lymphangiomas and hemangiomas also tend to disregard the compartment model. The former tend to be fluid in their attenuation and insinuate throughout, while the latter will be higher in attenuation.

Of course, lung cancer may present with metastases to any compartment and unfortunately and tends to metastasize to more than one region.

Key Point

  • Infections, lymphangiomas, and hematomas tend to disregard the compartmental model.

3.6 Conclusion

The mediastinum represents a space that may be impacted by a large number of lesions. Regardless whether one uses the modified Felson technique or the newer ITMIG approach, having an approach based on location and characterization will allow the radiologist the ability to create a useful, targeted differential diagnosis (Table 3.1).
Table 3.1

Location and characteristic approach to mediastinal masses in the adult

Take-Home Messages

  • A solid approach to the adult mediastinum uses the patient’s age, lesion cross-sectional attenuation/intensity, and lesion location to generate the differential diagnosis.

  • This compartment model is based on certain anatomic landmarks (Fig. 3.1).

  • Although most lesions will be characterized by CT, MR may have additional value in characterizing cystic lesions, diagnosing thymic hyperplasia and separating neurogenic from osseous lesions in the posterior mediastinum/paravertebral compartment.

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Authors and Affiliations

  1. 1.Mallinckrodt Institute of Radiology, Washington UniversitySaint LouisUSA
  2. 2.Radiology DepartmentThe Chaim Sheba Medical Center, Tel Aviv UniversityRamat GanIsrael
Sours: https://link.springer.com/chapter/10.1007/978-3-030-11149-6_3
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Publicationdate

This review is based on a presentation given by Sanjeev Bhalla and was adapted for the Radiology Assistant by Marieke Hazewinkel and Robin Smithuis.
Sanjeev Bhalla is section chief of the Cardiothoracic Imaging Section of the Mallinckrodt Institute of Radiology.

This review will focus on how to narrow down the differential diagnosis of mediastinal lesions by localizing and characterizing them.

Introduction

Whenever you see a mass on a chest x-ray that is possibly located within the mediastinum, your goal is to determine the following:

  • Is it a mediastinal mass?
  • Is it in the anterior, middle or posterior mediastinum?
  • Are you able to characterize the lesion by determining whether it has any fatty, fluid or vascular components?

The table on the left is the overall table for mediastinal masses.
In the next paragraphs we will discuss each compartment separately.

Statistically, it is important to remember the following:

  • Most masses (> 60%) are:
    • Thymomas
    • Neurogenic Tumors
    • Benign Cysts
    • Lymphadenopathy (LAD)
  • In children the most common (> 80%) are:
    • Neurogenic tumors
    • Germ cell tumors
    • Foregut cysts
  • In adults the most common are:
    • Lymphomas
    • LAD
    • Thymomas
    • Thyroid masses

Localize to the mediastinum

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.

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.

A lung mass abutts the mediastinal surface and creates acute angles with the lung, while a mediastinal mass will sit under the surface creating obtuse angles with the lung (Figure).

On the left you see two different patients.
Describe the findings and continue.

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.
The chest radiograph on the right shows a lesion with an obtuse angle to the mediastinum.
This must be a mediastinal mass.
Since there is a silhouette-sign with the right heart border - which is located anteriorly - we can deduce that the mass must be located within the anterior mediastinum.

The lesion on the left was a pancoast tumor.
The lesion on the right was a thymoma, located within the anterior mediastinum.

Localize within the mediastinum

The mediastinum can be divided into anterior, middle and posterior compartments.
It is important to remember that there is no tissue plane separating these compartments.

On the lateral radiograph the anterior and middle compartments can be separated by drawing an imaginary line anterior to the trachea and posteriorly to the inferior vena cava.
The middle and posterior compartments can be separated by an imaginary line passing 1 cm posteriorly to the anterior border of the vertebral bodies.
This division allows us to make a more narrow differential diagnosis.

In many hospitals a CT will be made to further analyze and characterize anterior and middle mediastinal masses.
An MRI is usually made to analyze masses located in the posterior compartment because the majority of these masses turn out to be neurogenic in nature.
An additional CT can be performed, when bone needs to be assessed.

Anterior Mediastinum

The anterior mediastinum contains the following structures: thymus, lymph nodes, ascending aorta, pulmonary artery, phrenic nerves and thyroid.

The most common lesions that you will see in the anterior mediastinum will either be of thymic or lymph node origin.
Even the germ cell tumors arise from the pluripotent cells of the thymus.
Before you want to biopsy an anterior mediastinal mass, do not forget thta some of these lesions can be vascular in origin.

The four T's make up the mnemonic for anterior mediastinal masses::

  1. Thymus
  2. Teratoma (germ cell)
  3. Thyroid
  4. Terrible Lymphoma

On conventional radiographs look for the signs listed in the table on the left.

The finding of an obliterated retrosternal clear space is not so helpfull anymore, since nowadays many patients are obese.
In these patients the retrosternal space can be filled with fat.

Obliterated retrosternal clear space

Describe the images on the left.
Then continue.

On the PA film there is a lobulated widening of the superior mediastinum.
On the lateral chest film the retrosternal clear space is obliterated.

This happened to be a patient with lymphoma.

On the left FDG-PET images of the same patient.
There are multiple lymphatic masses in the anterior, middle and even posterior mediastinum, spreading to the neck.

Hilum Overlay Sign: hilar vessels are seen through a mediastinal mass

Hilum Overlay Sign

When there is a mediastinal mass and you still can see the hilar vessels through this mass, then you know the mass does not arise from the hilum.
This is known as the hilum overlay sign.
Because of the geometry of the mediastinum most of these masses will be located in the anterior mediastinum.

Describe the images on the left.
Then continue.

On the chest film there is a mass that has obtuse angles with the mediastinum, so it is a mediastinal mass.
The hilar vessels are seen through this mass, so it does not arise from the hilum and probably will arise from the anterior mediastinum.
The anterior location was confirmed on a CT.
Most commonly this will be a mass of thymic or lymphatic origin.
This proved to be a lymphoma in a HIV-positive patient.

Cystic masses

The anterior mediastinum is an important location for cystic masses.
Masses can be entirely cystic (thymic cysts) or have solid components (lymphoma or cystic thymoma).
Some masses are cystic with enhancing septations - in these cases you should think of a germ cell tumor.

Describe the image on the left.
Then continue.

The CT shows an anterior mediastinal mass with water density attenuation.
This is typical for a thymic cyst.

Describe the image on the left.
Then continue.

The CT shows a mass located in the anterior mediastinum.
The mass is cystic but has solid enhancing septa.
This finding is very specific for a germ cell tumor.

Now many think that germ cell tumors contain fat and if a lesion does not contain fat, it cannot be a germ cell tumor.
You have to remember, that only about 60 % of germ cell tumors contain fat, so you must realize that the absence of fat does not exclude a germ cell tumor from the differential diagnosis.
The more solid components a germ cell tumor has, the more likely the tumor is to be malignant.

Describe the image on the left.
Then continue.

The CT shows a mass located in the anterior mediastinum.
The mass is cystic but has solid enhancing components, so we are worried about lymphoma, germ cell tumor and cystic thymoma.
This proved to be a cystic thymoma.

Middle Mediastinum

The middle mediastinum contains the following structures: lymph nodes, trachea, esophagus, azygos vein, vena cavae, posterior heart and the aortic arch.

The majority of middle mediastinal masses will consist of foregut duplication cysts (eg oesophageal duplication or bronchogenic cysts) or lymphadenopathy.
Aortic arch anomalies can also present as middle mediastinal masses.

Fluid containing lesions are usually duplication cysts or necrotic lymph nodes.
A pancreatic fluid collection due to pancreatitis may also present as a mediastinal mass.
A fibrovascular esophageal polyp is a mesenchymal lesion which almost always contains fat.
Vascular lesions are arch anomalies, azygos continuation due to interrupted inferior vena cava or hyperenhancing lymph nodes.

On conventional radiographs look for the signs listed in the table on the left.

Displaced azygoesophageal recess wiil be seen on the right.
On the left you may have a pseudoparavertebral line.
This is a new interface that looks like a paravertebral line.

Describe the image on the left.
Then continue.

On the AP chest radiograph of this patient there is widening of the azygoesophageal recess on the right.
There is an apparent widening of the paravertebral line on the left.
On the lateral film the mass is anterior to the spine and therefore is located in the middle mediastinal.

On the CT the azygoesophageal recess is displaced to the right due to oesophageal varices (blue arrow) and there is also a new interface on the left.
This is a patient with cirrhosis of the liver and varices as a result of portal hypertension.

On the left a patient with a small cell lung carcinoma.
Describe the images on the left.
Then continue.

On the PA film there is a lobulated paratracheal stripe on the right.
On the lateral radiograph there is a density overlying the ascending aorta and filling the retrosternal space.
These findings indicate a mass in the anterior aswell as in the middle mediastinum.

The CT confirms the presence oof lymphomas in both the anterior and the middle mediastinum.

On the left two different patients.
One of these patients has pulmonary hypertension and the other has sarcoidosis.
Describe the images on the left.
Then continue.

On the right image there is a lobulated mass surrounding the right bronchus creating a 'doughnut' with the bronchus as the hole in the doughnut.
On the left image there is only density in the area from 9 o'clock to 3 o'clock and not in the 3 - 9 o'clock area.
So the patient on the left has pulmonary hypertension with moderately enlarged vessels while the patient on the right has sarcoidosis with widespread lymphadenopathy.

When there is a density in the 3 - 9 o'clock area, there should always be concern about mediastinal masses.

Posterior Mediastinum

The posterior mediastinum contains the following structures: sympathetic ganglia, nerve roots, lymph nodes, parasympathetic chain, thoracic duct, descending thoracic aorta, small vessels and the vertebrae.

Most masses in the posterior mediastinum are neurogenic in nature.
These can arise from the sympathetic ganglia (eg neuroblastoma) or from the nerve roots (eg schwannoma or neurofibroma).
Don't forget lymphadenopathy, the vertebrae and the descending thoracic aorta as potential causes for posterior mediastinal masses.
Cystic lesions will be either neuroenteric cysts, schwannomas or meningoceles.
Fat containing lesions will be extramedullary hematopoiesis.
When the anemia is resolved the extramedullary marrow will stop producing blood and become fatty.

On conventional radiographs look for:

  • Cervicothoracic Sign
  • Widening of the paravertebral stripes

Cervicothoracic sign

The anterior mediastinum stops at the level of the superior clavicle.
Therefore, when a mass extends above the superior clavicle, it is located either in the neck or in the posterior mediastinum.
When lung tissue comes between the mass and the neck, the mass is probably in the posterior mediastinum.
This is known as the Cervicothoracic Sign.

If we study the image on the frontal view on the left, we see a mass extending above the level of the clavicle and there is lung tissue in front of it, so this must be a mass in the posterior mediastinum.

On the left the MR of the same patient.
It turned out to be a schwannoma.

On the left images of a patient, who has a disease, that is the most commonly missed diagnosis in the emergency department resulting in the number one cause of law suits.
Study the images and then continue.

Notice the widening of the paravertebral stripes on both the left and the right on the PA radiograph.
On the lateral radiograph there is a severely narrowed disc space.

The diagnosis is discitis.

On MR you will notice the edema of the soft tissues and the high signal intensity of the disc.

More than one compartment

Since there are no tissue planes separating the mediastinal compartments, there are lesions that do not respect our approach to the mediastinum.
These lesions tend to occupy more than one compartment and include: mediastinitis, hematomas, vascular entities, bronchogenic cancer, metastases and lymphangiomas (fluid containing).

Characterize

Once you have localized a mediastinal mass, next try to charcterize it by assessing whether it has any of the following characteristics:

  • Does the mass contain fluid?
  • Does it contain fat?/li>
  • Does it enhance following the administration of intravenous contrast?

Fluid containing masses

This is a list of mediastinal msses that may contain fluid:

  • Thymic Cyst
  • Thymoma
  • Teratoma
  • Pericardial Cyst
  • Foregut Duplication
  • Meningocoele
  • Neuroenteric Cyst
  • Cystic Lymphadenopathy
  • Lymphangioma

If a mass contains fluid it could be a teratoma (on the left) or a thymic cyst (on the right).
Note that this teratoma does not contain fat.
Teratomas are the most common benign germ cell tumors.
The most common malignant germ cell tumor is the seminoma.

Describe the image on the left.
Then continue.

There is are multiple masses in both the anterior and middle mediastinum.
The attenuation values are of water density.
These findings favor the diagnosis of cystic lymphadenopathy in a patient with metastatic disease.

Describe the image on the left.
Then continue.

There is a cystic lesion in the middle mediastinum.
There is a fluid fluid level with milk of calcium.
Foregut duplication cysts occasionally contain milk of calcium like in this example of an esophageal duplication cyst.

Fat containing masses

The differential diagnosis of fat containing mediastinal masses is:

  • Thymolipoma
  • Teratoma (Germ cell tumors)
  • Esophageal lipoma
  • Fat deposition
  • Lipoma
  • Lipoblastoma
  • Liposarcoma
  • Extramedullary hematopoiesis

On the left we see an fat-containing anterior mediastinal mass.
This is the typical finding of a fat-containing teratoma.

Describe the image on the left.
Then continue.

The axial CT and sagittal MR demonstrate a lipomatous lesion within the lumen of the esophagus.
This is typical for a esophageal lipoma and its fibrovascular stalk.

Multiple enhancing lesions in multiple compartments

Enhancing masses

The differential diagnosis of enhancing mediastinal masses is:

  • Hyperenhancing lymph nodes
  • Thyroid tissue
  • Paragangliomas
  • Hemangiomas
  • Vascular Etiologies

On the left multiple enhancing lesions.
This is typical for hyperenhancing lymph nodes.

Enhancing lymphomas can be seen in:

  • Melanoma
  • Renal cell carcinoma
  • Thyroid carcinoma
  • Castlemann's disease (as in this case)
Enhancing posterior mediastinal mass in a child.

Describe the image.
Then continue.

First notice the large thymus in this young child.
There is also an enhancing mass in the posterior mediastinum extending into the vertebral canal.
This is typical for a hemangioma.

Describe the image.
Then continue.

Somewhat irregular enhancing mass in the anterior mediastinum.
This proved to be a thyroid mass.

Sours: https://radiologyassistant.nl/chest/mediastinum/masses-differential-diagnosis
Approach to Mediastinal Masses

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Fluid collection mediastinal

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Mediastinal Masses A Diagnostic Approach - Edith MAROM

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