The mediastinum BY Dr Nikhil Bansal

The MediastinumBy Dr Nikhil Bansal

Introduction•Mediastinal disease is usually initially demonstrated

on a CXR and appear as a mediastinal soft tissue mass, widening or pneumomediastinum.

•However it may appear normal in the presence of mediastinal disease which is subsequently clearly demonstrated by CT or MRI.

NORMAL ANATOMY

Mediastinal Boundaries

Compartment Anteriorly Posteriorly

Anterior Sternum Anterior aspect of trachea and posterior margin of heart

Middle Anterior aspect of trachea and posterior margin of heart

A vertical line drawn along the thoracic vertebrae 1 cm behind their anterior margins

Posterior Vertical line drawn along the thoracic vertebrae 1 cm behind their anterior margins

Costovertebral junction

A M P

Mediastinal ContentsCompartment Main Strictures

Anterior Fat, lymph nodes, thymus, heart, ascending aorta

Middle Trachea, bronchi, lymph nodes, oesophagus, descending aorta

Posterior Para vertebral soft tissues

Mediastinal MassesCompartment % Malignant

Anterosuperior 59Middle 29

Posterior 16

Approach

1. Is the mass actually in the mediastinum or is it in the lung?

2. If in the mediastinum, then in which compartment?

3. What is the differential diagnosis for the mass?

•PA and lateral chest films are the first step in distinguishing from which mediastinal compartment the mass is arising from.

•CT & MRI 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.

Investigations

Clues to locate mass to mediastinum

Mediastinal masses are lined by parietal pleura, so will have:

Masses in the lung parenchyma typically:

– Smooth contour– Tapered borders– May be seen

bilaterally

– Are surrounded by air

– May contain air bronchograms

– Will be on one side only

Which compartment?

1. Cervicothoracic sign2. Thoracoabdominal sign3. Hilum overlay and convergence signs4. Effect on adjacent structures

Trachea Ribs Heart

Cervicothoracic sign•Described by Felson:

▫“If a thoracic lesion is in anatomic contact with the soft tissues of the neck, its contiguous border will be lost.”

•The anterior mediastinum ends at the level of the

clavicles.•The posterior mediastinum extends much higher.

•Therefore▫any mass that remains sharply outlined in the

apex of the thorax must be posterior and entirely within the chest, and 

▫any mass that disappears at the clavicles must be anterior and extends into neck

Cervicothoracic sign

Which compartment do you think this mass is in?

Click for lateral view

See sharp margin

above clavicle

Click for lateral view

Click for answer

Click for answer

Thisshouldhelp!

Cervicothoracic sign•Answer: Mass is in posterior mediastinum. We

know because it remains sharply outlined in apex of thorax, indicating that it is surrounded by lung.

•This particular example is a ganglioneuroma

Cervicothoracic sign

Which compartment do you think this mass is in?

Click for answer

Mass “disappears” at clavicle

Click for answer

Cervicothoracic sign•Answer: Mass lies in anterior mediastinum. We

know this because it disappears at the level of the clavicle where it extends into the neck.

•This particular example is Non-Hodgkins lymphoma

Thoracoabdominal sign•A sharply marginated mediastinal mass seen through

the diaphragm must lie entirely within the chest.•The posterior costophrenic sulcus extends far more

caudally than the anterior aspect of the lung

•Therefore▫Any mass that extends below the dome of the

diaphragm and remains sharply outlined must be in the posterior compartments and surrounded by lung, and

▫Any mass that terminates at dome of diaphragm must be anterior

Click for answer

Can you see the

outline of themass below

the diaphragm?

Click for answer

Thoracoabdominal sign

•Answer: Margin of mass is apparent and below diaphragm, therefore this must be in the middle or posterior compartments where it is surrounded by lung

•This example is a ‘Lipoma’

Hilum overlay and convergence signs

• Principle of hilum overlay▫The proximal

segments of the R and L main pulmonary arteries lie lateral to the cardiac silhouette on PA film

• With pericardial effusion or cardiac enlargement, this relationship is unchanged

• An anterior mediastinal mass will overlap the main pulmonary arteries, therefore they will be seen within the margins of the mass

• Hilum convergence▫To distinguish

between enlarged pulmonary artery and mediastinal mass

• If branches of the pulmonary artery converge toward a central mass enlarged PA

• If branches of PA converge toward the heart rather than the central mass mediastinal tumor

Hilum overlay sign

Can you see the pulmonary arteries on the following radiograph?

Click for answer

Hilum can be seen through mass

Click for answer

Hilum overlay sign

•Answer: this must be an anterior mediastinal mass because it overlaps rather than “pushes out” the main pulmonary arteries

•This particular example is a thymoma

Can you see the pulmonary arteries on the following radiograph?

Yes!!

Click for more info

Hilum overlay sign

•Heart is enlarged, but hilar vessels still visible lateral to the cardiac silhouette

•This case is pericardial effusion

Effect on adjacent structures

•Trachea▫May see deviation or narrowing of trachea with

anterior compartment masses

•Ribs/ vertebrae▫May see bony destruction with posterior

compartment masses

Anterior Mediastinal Masses (30% of mediastinal masses)

•The 4 T’s▫Thymoma

Generally over age 40▫Teratoma

Generally under age 40▫Thyroid

Goiter or neoplasm▫Terrible lymphoma

Thymoma

•Clinical clues▫ 70% of cases in patients

ages 40-60▫ Associated with

myasthenia gravis (in 50%)

pure red cell aplasia (in 5%)

Hypogammaglobulinemia (in 5%)

▫ Asymptomatic in 20-50%

▫ 35% are invasive▫ Tx: resection + RT if

invasive

•Radiographic clues▫ Often overlies

aortopulmonary window▫ Punctate, ringlike

calcification in 20%▫ Usually seen

unilaterally▫ 25-50% are

undectectable on CXR CT is better at 91% sensitivity

Thymic cyst

•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.

Teratoma

•Clinical clues

▫ Most patients < 30 y.o.▫ 50-75% symptomatic

with cough, dyspnea, chest pain

•Radiographic clues

▫ Well-defined, rounded or lobulated mass

▫ May contain calcification, teeth or fat

▫ Commonly have fluid-containing cystic areas

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

Thyroid goiter

•Clinical clues

▫ Affect females > males (3:1)

▫ Account for 10% of anterior mediastinal masses

▫ Usually asymptomatic

•Radiographic clues

▫ + cervicothoracic sign▫ Often displace or

narrow trachea▫ Calcification seen in

25%, and is dense and well-defined

Thyroid goiter

Trachea is deviated

to left

Mass disappears at level of

clavicle

Lymphoma

•Clinical clues

▫ Hodgkins (Reed-Sternberg cells)

▫ Bimodal distribultion: in 20s and at age >50

▫ Account for only 20-30 of all lymphomas but accounts for up to 85% mediastinal lymphoma

▫ 20-30% pts have “B” sx▫ Non-Hodgkins▫ Age > 55▫ Accounts for 80% of

lymphomas but only 20% present as mediastinal mass

•Radiographic clues

▫ Identical findings for Hodgkins and Non-Hodgkins lymphoma

▫ Mass may be multi-lobular

▫ Usually affects multiple nodes

▫ Often extends beyond anterior compartment

▫ Calcification rare prior to treatment

Mass disappears at level of

clavicle

PA and lateral chest films show a large, lobulated anterior mediastinal mass displacing the trachea to the right.

Twelve year old female with a chest mass

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 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

Germ Cell TumoursIt is a well defined round or oval soft tissue mass, which usually project to only one side of the anterior mediastinum. The soft tissue mass may also contain a peripheral rim or central nodular calcification or even a rudimentary tooth. A rapidly increase in the size of the mass show internal hemorrhage or development of malignancy.

Fat Deposition There is smooth widening of the superior mediastinum without trachial displacement.

Pleuropericardial cyst:

They appear as a well defined round, oval or triangular soft tissue mass which can alter in shape on respiration.

Anterior and middle mediastinal lymph node enlargement

Thoracic aorta aneurysm

Middle Mediastinal Masses (30% of mediastinal masses)

•The 4 A’s▫Adenopathy

TB/fungal Sarcoid Neoplasm (bronchogenic CA, mets, lymphoma, leukemia) Infections (EBV, AIDS)

▫Awful primary neoplasm Tracheal, esophageal

▫Aneurysm/vascular▫Abnormalities of development

Bronchogenic cyst- often between carina and esophagus Pericardial cyst Esophageal duplication cyst

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

Bronchogenic cysts

• 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.

Paratracheal Cystic Lesion

Posterior Mediastinal Masses: (40% of mediastinal masses)•Neurogenic tumors most common

▫Sympathetic ganglion tumors: neuroblastoma, ganglioneuroma

▫Nerve root tumors: schwannoma, neurofibroma• Less common

▫Vertebral body abscess or tumor▫Vascular: aneurysm or hematoma▫Developmental: Bochdalek hernia

Neural tumors

•Clinical

▫ 70-80% are benign▫ 50% of pts are

asymptomatic▫ Schwannoma is the

most common▫ Tx: resection

•Radiographic findings

▫ Well-defined mass with a smooth or lobulated outline

▫ Can be very large▫ +/- calcification

Posterior mediastinal mass

What is the finding in the following radiograph?

Click to see lateral view

Can easily see

posterior location

Posterior mediastinal mass

What is it? ‘Shwannoma’

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 main stem bronchus.

• Dx:Lipoma, Posterior Mediastinal

Descending aorta aneurysm

Bochdalek hernia

Thank You

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.Dx-Sequestration, Extralobar

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.

Dx-Neuroblastoma