MEDIASTINAL MASSES

• The mediastinum is defined as the tissue compartment located between the two lungs, posterior to the sternum, anterior to the vertebral column, and extending from the thoracic inlet to the diaphragm.

• Superior - imaginary line traversing the manubriosternal joint and the lower surface of the fourth thoracic vertebra.

• Inferior – Anterior

Middle

Posterior

• Felson’ method - line extending from the diaphragm to the thoracic inlet along the back of the heart and anterior to the trachea separates the anterior and middle mediastium.

• A line that connects points 1 cm behind the anterior margins of the vertebral bodies separates the middle and posterior mediastinal compartments.

Anterior Mediastinum

• Boundaries - anteriorly by the sternum;

posteriorly by the pericardium, aorta, and

brachiocephalic vessels; superiorly by the

thoracic inlet; and inferiorly by the diaphragm.

• Contains - thymus, lymph nodes, adipose

tissue, and internal mammary vessels

Anterior Junction Line• The line is formed by the anterior apposition of the

lungs and consists of the four layers of pleura

separating the lungs behind the upper two-thirds of

the sternum.

• The line runs obliquely from upper right to lower left and does not extend above the manubriosternaljunction.

• Contains variable amount of fat.

Posteroanterior chest radiograph demonstrates the anterior junction line

CT scan shows the four layers of pleura that constitute the anterior junction line

Posteroanterior chest radiograph demonstrates the anterior junction line

Mediastinal mass

• No air bronchogram

• Margins with lung obtuse

• Mediastinal lines will be disrupted.

• Can be associated spinal ,costal or sternalabnormalities

SIGN FOR LOCALISATION

• SILHOUETTE SIGN

• HILUM OVERLAY SIGN

• HILUM CONVERGENCE SIGN

• CERVICO-THORACIC SIGN

• THORACO ABDOMINAL SIGN

ISilhouette sign

• If an intrathoracic opacity is situated inanatomic contact with a border of heart oraorta ,will obscure that border.

A radioopacity causes obliteration of rt border ofheart , is anterior in location ,Anteriormediastinum.

If it overlaps but does not obliterates , it lies inposterior or middle mediastinum.

Silhouette sign

Hilum overlay sign

• Differentiates cardic enlargement frommediastinal mass

• In mediastinal mass if Hilar vessels are seenthrough the mass indicates that the mass does not arise from hilum

• For accuracy the film should be true frontal,slight obliquity may project normal pulmonary artery medialy

Hilum overlay sign

Cervicothoracic sign

Well defined mass seen above the clavicle is

always situated in posterior compartment ,the

anterior compartment mass being in contact

with soft tissue rather than aerated lung is ill

defined

Cervicothoracic sign

Anterior mediastinal masses

• Displaced anterior junctional lines

• Obliterated cardiophrenic angle

• Obliterated retrosternal clear space

• Hilum overlay sign

• Anterior mediastinal masses

prevascular - Thymic masses

- Retrosternal thyroid

- Teratoma

- Lymph nodal mass

precardiac - Epicardial fat pad

- Morgagni ‘ s hernia

- pleuropericardial cyst

- Anterior mediastinal masses in the prevascular region can obliterate the anterior junction line.

Middle Mediastinum• Boundaries - anteriorly by

the pericardium, posteriorlyby the pericardium and posterior tracheal wall, superiorly by the thoracic inlet, and inferiorly by the diaphragm.

• Contains - heart and pericardium; the ascending and transverse aorta; SVC and IVC; the brachiocephalicvessels; the pulmonary vessels; the trachea and main bronchi; lymph nodes; and the phrenic, vagus, and left recurrent laryngeal nerves.

Right Paratracheal Stripe

• The right paratracheal stripe is seen projecting through the SVC. It is formed by the trachea, mediastinal connective tissue, and paratracheal pleura and is visible due to the air–soft tissue interfaces on either side.

• paratracheal stripe should be uniform in width with a normal width ranging from 1 to 4 mm.

• The azygos vein lies at the inferior margin of the right paratracheal stripe at the tracheobronchial angle.

Posteroanterior chest radiograph shows

the right paratracheal stripe (arrow).

The azygos vein is seen at the inferior

margin of the stripe at the

tracheobronchial angle.

CT scan shows the right wall of the

trachea with medial and lateral air–soft

tissue interfaces caused by air within the tracheal lumen

and right lung.

The right paratracheal stripe can be widened due to abnormality of any of its components, from the

tracheal mucosa to the pleural space.

Middle Mediastinal Masses

• Lymphadenopathy

• Aortic aneuyrsm

• Enlarged pulmonary artery

• Foregut duplication cyst

• Tracheal lesions

Posterior Mediastinum

• The posterior mediastinum is bounded anteriorly by the posterior trachea and pericardium, anteroinferiorlyby the diaphragm, posteriorlyby the vertebral column, and superiorly by the thoracic inlet.

• Contents -Esophagus, descending aorta, azygos and hemiazygos veins, thoracic duct, vagus and splanchnicnerves, lymph nodes, and fat

Posterior

• Extent: posterior to a line 1 cm behind the anterior margin of the vertebral column, anterior to the chest wall

Posterior Mediastinal Masses

• Esophageal lesions, hiatal hernia

• Foregut duplication cyst

• Descending aorta aneuyrsm

• Neurogenic tumour

• Paraspinal abscess

• Lateral meningocele

• Extramedullary haematopoiesis

Azygoesophageal Recess

• The azygoesophageal recess is the interface between the right lung and the mediastinal reflection, with the esophagus lying anteriorly and the azygos vein posteriorly within the mediastinum.

• On X-ray,it appears as a line –

- in its upper 1/3rd , it deviates to the right at the level of the carina to accommodate the azygos vein arching forward.

- middle 1/3rd , the line has a variable appearance: It is usually straight.

- lower 1/3rd , usually straight. ( air in esophagus)

Posteroanterior chest radiograph shows the azygoesophageal line

CT scan shows the azygoesophageal recess

(white arrow) formed by the esophagus

anteriorly (black arrow) and the azygos vein

posteriorly(arrowhead).

• The azygoesophageal recess reflection is a pre-vertebral structure and is, therefore, disrupted by prevertebral disease.

• It has an interface with the middle mediastinum; thus, the resulting line seen at radiography can be interrupted by abnormalities in both the middle and posterior compartments.

Posteroanterior chest radiograph demonstrates a subcarinal abnormality with increased opacity (*), splaying of the carina, and abnormal convexity of the

upper and middle thirds of the azygoesophageal line (arrowheads)

Corresponding CT scan helps confirm a subcarinal mass (arrow), which proved to be a bronchogenic cyst.

Posterior Junction Line

• Seen above the level of the azygos vein and aorta and that is formed by the apposition of the lungs posterior to the esophagus.

• usually extend from third to fifth thoracic vertebrae.

• posterior junction line can be seen above the suprasternal notch and lies almost vertical, whereas the anterior junction line deviates to the left.

Collimated posteroanterior chest radiograph shows the posterior junction line (arrow) projecting through the tracheal air column.

CT scan shows the posterior junction line (arrow), which is formed by the interface between the lungs posterior to the mediastinum and

consists of four pleural layers.

Posteroanterior chest radiograph shows a mass (arrow) obliterating the posterior junction line. Note that the mass extends above the level of the clavicle and has a well-demarcated outline due to the

interface with adjacent lung (arrowhead).

CT scan helps confirm the posterior location of the mass (arrow), which proved to be a bronchogenic cyst.

Paraspinal Lines

• The paraspinal lines are created by the interface between lung and the pleural reflections over the vertebral bodies.

• The left paraspinal line is much more commonly seen than the right. The descending aorta holds the pleural reflection off the vertebral body, allowing the lung–soft tissue interface to be more tangential to the x-ray beam.

• The left paraspinal line runs parallel to the lateral margin of the vertebral bodies and can lie anywhere medial to the lateral wall of the descending aorta

On a collimated posteroanterior

chest radiograph, the left

paraspinal line (arrow) is seen separate and

distinct from the vertebral body

(black arrowhead) and the descending thoracic aorta

CT scan shows the left paraspinal line. The descending aorta holds the pleural reflection (arrow) away from the vertebral body, which allows the lung–soft

tissue interface to be more tangential to the x-ray beam and therefore visualized as a line

• The paraspinal lines are disrupted by paravertebral disease—which commonly includes diseases originating in the intervertebral disks and vertebrae—and by neurogenic tumors.

Posteroanterior chest radiograph shows a mass (arrow) effacing the left paraspinal line. The lateral wall of the descending aorta is seen as a separate

entity (arrowhead).

CT scan shows a paraspinal abscess (arrow) effacing the paraspinal lines. The air–soft tissue interface between the lung and aorta remains intact (arrowhead), thereby preserving the normal radiographic appearance of

the lateral aortic wal

Posteroanterior chest radiograph shows lateral displacement of the lateral margin of the descending thoracic aorta due to an aortic aneurysm

(arrowheads).

CT scan also demonstrates the aneurysm (arrow).

THE NORMAL THYMUS

• The thymus has two lobes, the right and the left, which are fused superiorly near the thyroid gland and smoothly molded to the anterior aspect of the great vessels and anterior heart.

• It occupies the thyropericardic space. The thymus is rarely found in an ectopic location, usually the neck.

• The left thymic lobe usually is larger than the right.

Thymus gland

• Roughly a bi-lobed structure

• DEVELOPMENT- bilateral 3rd pharyngeal pouches

• EVOLUTION- largest at birth or during infancy increases slightly during 1st decade of life and decrease thereafter.

• Normal weight- 5 – 50 gm

Radiology of thymus gland

• On conventional chest radiograph it is consistently visible only in infants and young childrn then after 2-3 yrs of age it becomes an inconstant feature

• Three radiographic signs aid identification of normal thymus gland

1. THYMIC NOTCH SIGN

2. SAIL SIGN

3. THYMIC WAVE SIGN

Radiology of thymus gland

Sail sign

• SAIL SIGN-

present only in 5% of infants related to the presence of a triangular opacity of thymictissue that projects to the left or right

Thymus wave sign

• THYMUS WAVE SIGN-

Seen as an undulating or rippled contour of thymus border caused by anterior rib indentation

• THYMUS NOTCH SIGN-

An indentation of thymus contour at the junction of heart and thymus

CT• In children, the normal thymus fills the prevascular space, draping itself over the

great vessels and cardiac margins .• Cephalad, the thymus extends above the innominate vein .• In infancy, the thymus is commonly seen to the level of the pulmonary arteries or

below, but its inferior extent decreases with age.• In infants and young children, the thymus appears quadrilateral on CT. As the child

grows, the thymus assumes a more triangular shape, often appearing arrowhead shaped or bilobed, with each of the two thymic lobes contacting the mediastinal pleura.

• Its margins are sharp, smooth, and convex in infants and often become straight in older children.

• Each lobe usually measures 1 to 2 cm in thickness (perpendicular to the pleura), but this is variable.

• On unenhanced CT, the thymus is approximately the same attenuation as muscle. • The mean attenuation of the thymus has been found to be 36 HU; the thymus shows

homogeneous enhancement of 20 to 30 HU after bolus contrast injection.

• Over the age of 25 years, the thymus is no longer recognizable as a soft-tissue structure on CT because of progressive fatty involution

Normal thymus in a 21-year-old patient. The thymus occupies the prevascular space and appears triangular and of soft-tissue attenuation, the left lobe (LL) being larger than the right (RL).

Normal thymus in a 51-year-old patient. The thymus (arrows) appears to be composed primarily of fat, containing islands or wisps of soft tissue. The left thymic lobe extends more posteriorly than the right.

THYMIC LYMPHOID FOLLICULAR HYPERPLASIA

• The term thymic lymphoid follicular hyperplasia (LFH) is used to describe a condition characterized by the presence of hyperplasticlymphoid germinal centers in the thymic medulla, associated with a lymphocytic and plasma cell infiltrate.

• The presence of LFH is commonly associated with myasthenia gravis, connective tissue disease, pure red blood cell hypoplasia, and infection with HIV;

• it may also be seen in some normal young subjects.

• Plain radiographs are usually normal. On CT, patients with LFH can have a normal-appearing thymus (45%), an enlarged thymus with a normal shape (35%), or a focal thymus mass (20%)

Thymic lymphoid follicular hyperplasia. A focal mass (arrow) in the prevascular space represented follicular hyperplasia. Its appearance is nonspecific and cannot be distinguished from thymoma.

THYMIC HYPERPLASIA• Thymic hyperplasia, as distinguished from LFH, is defined by an

increase in size of the thymus associated with an otherwise normal gross and histologic appearance.

• It may be associated with hyperthyroidism (Graves' disease, sarcoidosis, red blood cell aplasia, and other entities.

• It most commonly is seen in association with recovery from chemotherapy, stress, or burns, a phenomenon known as thymicrebound (described below).

• Chest radiographs in adults are usually normal.

• In children, thymic enlargement may be seen.

• CT demonstrates increased thickness of the thymic lobes but an otherwise normal-appearing thymus

Thymic hyperplasia in Graves' disease. A. Chest radiograph in a 40-year-old woman shows mediastinal widening (arrows). B and C. CT shows enlargement of the thymus (T) in the prevascular space. The left thymic lobe is largest

Thymic Rebound

• The thymus involutes during periods of stress (e.g., burns, chemotherapy) and may decrease significantly in size

• the thymus will generally regrow to its original size within several months of the stressful episode

• The presence of lymph node enlargement in association with thymic enlargement should suggest recurrent tumor, while isolated thymic enlargement should suggest thymic rebound

THYMOMA

• Originates from thymic epithelium

• Most common thymic tumor

• 15%-20% of mediastinal masses

• Most common in patients 50-60 years old

• Myasthenia gravis in 30%-50%

• 10%-30% of patients with myasthenia have thymoma

• Invasive (30%) or noninvasive (70%), not benign and malignant

• Metastases outside thorax in 3%-5%

Plain Radiographs

• Most thymomas occur near the junction of the heart and great vessels, although they may be seen superiorly to the level of the clavicles and inferiorly to the level of the costophrenic angles.

• Thymomas typically appear sharply marginated, smooth or lobulatedin contour, and usually project to one side of the mediastinum.

• They usually range in size from 5 to 10 cm in diameter when visible on radiographs, and may obscure the right or left heart border, depending on their location and size.

• Dense calcification may be seen in the periphery of the mass or throughout its substance.

• On lateral radiographs, thymoma often produces a distinct opacity in the inferior aspect of the retrosternal clear space, the relatively lucent triangular region posterior to the sternum and anterior to the aortic arch, main pulmonary artery, and heart

CT

• In nearly all cases, thymomas occur in the prevascular space and displace the great vessels (aorta and its branches, superior vena cava and its branches, and main pulmonary artery) posteriorly

CT shows a cystic (fluid attenuation) mass in the right cardiophrenicangle. The mass shows dense calcification, including calcification of its capsule. A noninvasive cystic thymoma was found at surgery.

• Thymoma or other thymic neoplasm may be distinguished from thymic hyperplasia if enlargement of the thymus is grossly asymmetric, if the thymus has a lobular contour, or if a focal rounded lesion is visible

Invasive thymoma with calcification in a patient with myasthenia gravis. A. CT shows a lobulated mass (T) in the prevascular space, typical of thymoma. Medially, the mass invades mediastinal fat (large arrow). A small pleural nodule (small arrow) is also seen, resulting from pleural invasion. Compression of the superior vena cava is also present. B. At a lower level, calcification is visible.However, follicular thymic hyperplasia can

result in a focal thymic mass up to 5 cm in diameter

• Approximately 80% of thymomas occur at the base of the heart, as shown on CT .

• They usually appear as homogeneous soft-tissue attenuation masses that are sharply demarcated and oval, round, or lobulated and do not conform to the normal shape of the thymus

It is often difficult to distinguish invasive and noninvasivethymoma on CT

• Findings highly suggestive of invasion include

• pericardial thickening contiguous with the tumor, pleural thickening, nodules, or effusion,

• encasement of mediastinal structures,

• fat infiltration• an irregular interface

between the tumor and lung.

Invasive thymoma with calcification. CT shows a lobulated thymoma with multiple calcifications. The presence of pleural effusion strongly suggests invasion

Invasive thymoma with pleural metastases. A. PA chest radiograph shows a mass at the left cardiophrenic angle (arrows). B. CT shows a homogeneous rounded mass (T) representing thymoma. C. At a lower level, CT shows focal pleural thickening or nodules (arrows), typical of pleural metastases. Pleural nodules are usually unassociated with pleural effusion. This finding indicates invasion.

Noninvasive thymoma. A. CT shows a homogeneous thymoma (T) separated from the aorta (A) and pulmonary artery (P) by a layer of fat. B. Oblique sagittal reconstruction shows separation of the thymoma (T) from the ascending aorta (A).

THYMIC CARCINOMA

• Originates from thymic epithelium

• 20% of thymic epithelial tumors

• Average age 50

• Unlike thymoma, appears malignant histologically

• Invasion common, distant metastases in 50%-65%

• Myasthenia rare

• Appearance indistinguishable from thymomaunless metastases are visible

• Thymic carcinoma usually results in a mass 5 to 15 cm in diameter.

• A large mass with or without areas of low attenuation is typical .

• Calcification may be present .• Thymic carcinoma cannot be

distinguished from thymoma on CT unless enlarged lymph nodes are visible in the mediastinum or distant metastases are evident.

• Thymic carcinoma is less likely than thymoma to result in pleural implants.

THYMIC CARCINOID TUMOR

• Originates from neural crest cells.

• Average age 45

• Usually malignant

• Cushing's syndrome in 25%-40%

• MEN in 20%

• Mimics thymomaradiographically

• Dense enhancement possibly seen on CT

• This tumor is more aggressive than thymoma, being malignant in most cases, and superior vena cava obstruction is much more common with thymiccarcinoid than with thymoma.

• The 5-year survival rate is about 65%. Metastases may be visible.

Thymolipoma

• Consists of fat and thymic tissue

• 5% of thymic tumors

• Benign

• Often young patients

• Usually asymptomatic

• Large droopy mediastinal mass containing fat and strands of tissue

• In most cases, thymolipoma is unaccompanied by symptoms and is detected incidentally on chest radiographs.

• It is often large, averaging nearly 20 cm in diameter at diagnosis, and it may project into both hemithoraces.

• Because of its fatty content and pliability, thymolipoma tends to drape over the heart, extending inferiorly into the cardiophrenicangles.

• It can simulate cardiac enlargement, lower lobe collapse, or elevation of a hemidiaphragm .

• There is no known association with myasthenia gravis.

Thymic Cyst

• Thymic cysts are uncommon.

• They can be either congenital or acquired.

• One should be cautious in making the diagnosis of thymic cyst; cystic regions can be seen in a variety of thymic tumors, including thymoma and lymphoma..

• CT can suggest the diagnosis of thymic cyst if the lesion

• (1) appears thin-walled; (2) is unassociated with a mass lesion;

• (3) contains fluid with a density close to that of water; and

• (4) remains unopacifiedfollowing contrast infusion

Thymic Lymphoma and Metastases

• Hodgkin's disease (HD) has a predilection for involvement of the thymus in conjunction with involvement of mediastinal lymph nodes.

• Thymic enlargement may be seen in 30% of patients with intrathoracic HD.

• Non-Hodgkin's lymphoma (NHL) much less commonly involves the thymus.

• Thymic lymphoma usually results in homogeneous thymicenlargement.

• thymic mass with mass or lymph node enlargement in other areas of the mediastinum is suggestive of this diagnosis

GERM CELL TUMORS

• Germ cell tumors account for about 10% of primary mediastinal masses and arise from primitive germ cells that have arrested their embryologic migration in the mediastinum, frequently within the thymus.

• They are more common in the anterior mediastinum

• Germ cell tumors include benign and malignant teratoma, seminoma, embryonal carcinoma, endodermal sinus (yolk sac) tumor, choriocarcinoma, and mixed cell types.

• Overall, more than 80% of germ cell tumors are benign

TERATOMA

• Contains elements of all germinal layers• Mature teratomas (contain mature tissues)

Benign60%-75% of mediastinal germ cell tumorsOccur in children and young adultsDermoid cyst

• Immature teratomas (contain immature tissue)Often have benign course in infants or young childrenOften aggressive and malignant in adults

• Malignant teratoma (contains frankly malignant tissues)Poor prognosis

Usually menAnterior mediastinal mass; posterior in 5%Smooth, rounded, or lobulated mass

• Mature teratoma

• Well defined, smooth, cystic

• Teeth and bone rare

• Fluid in 90%; fat in 75%; calcification in 50%

• Immature or malignant teratoma

• Nodular or poorly defined

• Fat in 40%

• Compression or invasion of mediastinal structures

• Enhancing capsule

Mature mediastinal teratoma. A. PA chest radiograph shows a smooth, sharply marginated left mediastinal mass (arrows). It obscures the left heart border, indicating its anterior location. B. Lateral view shows increased density of the retrosternal clear space (arrow), but a discrete mass is not visible.

• Benign lesions are

• typically well defined, smooth, and cystic, and 90% contain fat.

• Malignant teratomasare nodular or poorly defined, they are more likely to appear solid, and a smaller proportion (40%) contains fat

. Mature mediastinal teratoma. A large mass is compressing right cardiac structures. It contains calcifications, areas of fat (arrow), and cystic or soft-tissue regions.

SEMINOMA

• 30% of germ cell tumors

• Mean age 29

• Large, lobulated, anterior mediastinal mass

• Homogeneous in attenuation

• Good prognosis; 5-year survival rate 50%-75%

Mediastinal seminoma. A. PA radiograph shows a large, lobulated, and poorly marginated mediastinal mass (arrows) obscuring the right heart border. A small right pleural effusion is also visible. B. Lateral view shows a large anterior mediastinal mass (arrows).

NONSEMINOMATOUS GERM CELL TUMOR

• Cell typesEmbryonal carcinomaEndodermal sinus (yolk sac) tumorChoriocarcinomaMixed types

• Large, lobulated, anterior mediastinal mass associated with pleural effusion because of local invasion of lung and pleura. ,

• Inhomogeneous in attenuation, including ill-defined areas of low attenuation secondary to necrosis and hemorrhageor cystic areas

• Poor prognosis

THYROID GLAND AND THYROID ENLARGEMENT

• The thyroid gland is located in close approximation to the thoracic inlet, and thyroid enlargement is commonly associated with extension into the mediastinum.

• Multinodular goiter is the most common condition in which a mediastinal thyroid abnormality is detected; carcinoma and thyroiditis are relatively rare causes.

MEDIASTINAL THYROID MASS

• 10% of mediastinal masses

• Almost always connected to cervical thyroid

• Anterior in 75%-90%; posterior in 10%-25%

• Masses high in attenuation on CT; densely enhance with contrast

• Cystic or inhomogeneous

• Punctate calcifications

• Distinguishing goiter and carcinoma difficult

Mediastinal goiter. A mass in the superior mediastinum (white arrows) is sharply defined inferiorly and poorly defined above the clavicles. The trachea is displaced to the left (black arrow).

Cystic cervical and mediastinal goiter. A. Chest radiograph shows displacement of the trachea to the right (arrow) and poorly defined superior mediastinal widening at the level of the thoracic inlet. B. CT shows an enhancing multicystic mass (arrows) at the level of the thoracic inlet. The trachea (T) is displaced to the right and slightly narrowed.

• Recognizing that a mediastinal mass originates from the thyroid gland depends on

• (1) demonstration of a communication with the cervical portion of the thyroid gland on contiguous slices

• (2) high attenuation of at least a portion of the mass

• (3) marked enhancement after contrast injection • (4) prolonged enhancement (more than 2

minutes).

Hodgkin's Disease• HD has a predilection for thoracic involvement, and up to 85% of

patients with HD present with mediastinal adenopathy.• HD most often involves the superior mediastinal (prevascular,

paratracheal, aortopulmonary) lymph nodes • Multiple node groups are commonly involved in patients with HD • In addition to superior mediastinal node groups, sites of lymph

node enlargement, in order of decreasing frequency, include hilarnodes, subcarinal nodes, cardiophrenic angle (paracardiac) lymph nodes, internal mammary nodes, and posterior mediastinal nodes.

• Enlargement of lymph nodes in a single node group can be seen in some patients with HD, most commonly in the anterior (prevascular) mediastinum.

• This often indicates the presence of nodular sclerosing HD, which accounts for 50% to 80% of adult HD cases.

Superior mediastinal lymph nodes in Hodgkin's disease. A. PA radiograph shows a mass (arrows) in the region of the aortopulmonarywindow. B. An anterior mediastinal mass (arrows) is visible on lateral chest radiograph.

Involvement of multiple lymph node groups in Hodgkin's disease. A and B. Involvement of pretracheal (small arrows) and prevascular(large arrows) nodes is common in Hodgkin's disease. C. At a lower level, paracardiac lymph node enlargement is also seen (arrows).

Non-Hodgkin's Lymphoma

• The term non-Hodgkin's lymphoma refers to a diverse group of diseases, varying in radiologic findings, clinical presentation, course, and prognosis. In comparison to HD, these tumorsare less common as causes of thoracic disease.

Bronchogenic Cysts

• 60% of foregut duplication cysts

• Wall contains respiratory epithelium, smooth muscle, mucous glands, or cartilage

• 50% subcarinal; 20% paratracheal; 10% retrocardiac

• Bronchogenic cysts can be present in any part of the mediastinum but are most commonly located in the middle or posterior mediastinum, near the carina (50%),

• Round, smooth, sharply defined

• Wall thin or invisible on CT; wall may calcify

• Fluid contents variable in attenuation on CT (0-40 HU)

• On plain radiographs, bronchogenic cysts appear as

1) smooth, sharply marginated, round or elliptical masses.

2) They may be large and displace the trachea or bronchi.

3) Subcarinal cysts may result in convexity in the superior aspect of the azygoesophageal recess.

• On CT, bronchogenic cysts usually appear rounded or elliptical, smooth in contour;

• The wall of a bronchogeniccyst appears thin or is imperceptible.

• Half of bronchogenic cysts are of water attenuation

• lack of enhancement on scans obtained following intravenous contrast infusion Bronchogenic cyst. A. A large subcarinal mass (arrows) is visible on

chest radiograph. B. Unenhanced CT shows a large subcarinalbronchogenic cyst (C, white arrows), appearing slightly less dense than soft tissue. Focal calcification of the cyst wall is visible (black arrow) C. Coronal T1-weighted MRI shows a large subcarinal cyst. Signal from the cyst (C) is due to its protein content. D. Transaxial T2-weighted, fat-saturated image shows high signal intensity. This is typical. C, cyst.

Neurogenic Tumors• Neurogenic tumors account for about 10% to 20% of primary mediastinal

masses in adults and 30% to 35% of mediastinal tumors in children. • Seventy-five percent of posterior mediastinal masses are neurogenic

tumors. • Tumors may arise from peripheral nerves and nerve sheath (neurofibroma,

schwannoma, malignant peripheral nerve-sheath tumors) or sympathetic ganglia (ganglioneuroma, ganglioneuroblastoma, neuroblastoma).

• The most common cell types are schwannoma (35%), ganglioneuroma(25%), neuroblastoma (15% to 20%), ganglioneuroblastomas (7% to 15%), and neurofibroma (5% to 10%), but the incidence varies with the patient's age.

• Eighty percent are benign.• Nearly 85% of tumors in children are of ganglionic origin, while in adults

more than 75% are nerve sheath tumors. • Specifically, schwannoma and neurofibroma are more common in adults,

while ganglioneuroblastoma and neuroblastoma are more common in children

PERIPHERAL NERVE SHEATH TUMORS

• Neurilemmoma (schwannoma), neurofibroma, and neurogenic sarcoma

• Most common in adults• Round, elliptical, or lobulated paravertebral mass• Often one or two interspaces in length• Rib or vertebral abnormalities in 50%• Lower attenuation than muscle in 70%• One third of patients with neurofibromas have

neurofibromatosis• Plexiform neurofibroma: extensive fusiform or

infiltrating mass

• On plain radiographs, nerve sheath tumors typically appear as sharply marginated round, elliptical, or lobulatedparavertebral masses, although they may be well seen only on the frontal radiograph

• They tend to be limited to one or two interspaces in length but in some patients can be large.

• Associated rib or vertebral deformity or enlargement of a neural foramen is visible in about 50% of cases Schwannoma. PA chest radiograph shows a

well-defined right mediastinal mass associated with deformity of right-sided ribs.

Schwannoma. A. PA chest radiograph shows a well-defined mass in the superior mediastinum(arrows). B. On the lateral view, the mass is relatively posterior in location (arrow). C. A well-defined homogeneous mass is visible on CT.

• On CT, nerve sheath tumors typically appear as wellmarginated, smooth, rounded or elliptical masses

• Enlargement of neural foramina may be better shown on CT than on plain films .

• In over 70% of cases, peripheral nerve or nerve sheath tumors appear to be lower in attenuation than chest wall muscle; in the remainder, they are of soft-tissue attenuation.

• Low-density areas within nerve sheath tumors can be due to the presence of (1) lipid-rich Schwann cells; (2) adipocytes; (3) perineural adipose tissue entrapped by plexiform neurofibromas; or (4) cystic spaces in the tumor.

• Variable enhancement of the tumor may be seen following contrast infusion

TUMORS DERIVED FROM SYMPATHETIC GANGLIA

• Ganglioneuroma, ganglioneuroblastoma, and neuroblastoma

• 20% of posterior masses in children

• Oblong or sausage-shaped paravertebral mass

• Calcification in 20%

Ganglioneuroma

• Ganglioneuroma, a benign tumor made up of Schwann cells, collagen, and ganglion cells, is a common neoplasm in teenagers and young adults.

• On plain radiographs, this tumor often appear as an oblong or sausage-shaped mass in a paravertebral location; they tend to be longer than nerve sheath tumors occurring in a similar location

• Ganglioneuroma cannot be distinguished from schwannoma or neurofibroma on the basis of its CT appearance.

• Calcification is seen in about 20% of cases, and vertebral abnormalities may be seen.

• On MRI, ganglioneuroma may appear homogenous in intensity on -T1- and

• T2-weighted images or may show a unique whorled appearance of layers of varying intensity

neuroblastoma

• Approximately 15% of neuroblastomas arise in the mediastinum, and almost all are located posteriorly.

• Mediastinal neuroblastoma is seen almost exclusively in young children under the age of 5 years.

• It is malignant

CT

• neuroblastomas appear as soft-tissue attenuation masses, but up to 40% contain speckled or curvilinear calcifications .

• They are most common in the paravertebral regions and may extend superiorly and inferiorly for several centimeters.

• Neuroblastoma often shows inhomogeneous enhancement following contrast injection.

• CT and MR may be used to help determine the presence and extent of mediastinal or vertebral column invasion.

• Invasion of the extradural spinal canal is common, even in the absence of neurologic signs and symptoms

Mediastinal neuroblastoma in a 16-month-old child. PA (A) and lateral (B) chest radiographs show a large superior, posterior mediastinal mass

CT shows a large paravertebral, posterior mediastinal mass containing small areas of calcification (arrows). D. T2-weighted MRI shows a large mass in the posterior mediastinum. The tumor extends into the spinal canal through a neural foramen (white arrow), displacing the spinal cord to the right (black arrow).