Diagnostic Imaging of Mediastinal Masses

ChestMediastinal Masses

Mohamed Zaitoun

Assistant Lecturer-Diagnostic Radiology Department , Zagazig University Hospitals

EgyptFINR (Fellowship of Interventional

Neuroradiology)-Switzerlandzaitoun82@gmail.com

Knowing as much as possible about your enemy precedes successful battle

and learning about the disease process precedes successful management

Mediastinum1-Anterior Mediastinal Masses2-Middle Mediastinal Masses3-Posterior Mediastinal Masses

Mediastinal lines or stripes are interfaces between the soft tissue of mediastinal structures and the lung, the aortopulmonary window is the interface below the aorta and above the pulmonary trunk and is concave or straight laterally

Anterior junction line results from the anterior apposition of the lungs, which lies behind the upper two-thirds of the sternum, the line consists of four layers of pleura and a variable amount of intervening fat, it appears as a thin oblique line projecting over the superior two-thirds of the sternum and runs from the upper right to the lower left, it does not extend above the level of clavicles, posterior junction line results from the apposition of the lungs posterior to the esophagus and anterior to the 3rd to 5th thoracic vertebrae, similarly to anterior junction line, it is formed by four layers of pleura, it appears as a thin straight line projecting through the trachea, unlike anterior junction line, it can be seen above the clavicles

Mediastinal signs, frontal chest film (a) shows the hilum (arrow), which indicates that the mass is either anterior or posterior to the hilum, this is the hilum overlay sign in patient with lymphoma, frontal chest film (b) shows enlargement of the right superior mediastinum, above the level of the clavicles, the margins of the mass are sharp (arrow) due to the interface with adjacent lung, indicating that the mass is located in the posterior mediastinum

1-Anterior Mediastinal Masses (5Ts)a) Thymus Abnormalitiesb) Thyroid Massesc) Terrible Mediastinal Lymphomad) Germ Cell Tumorse) Thoracic Aortic Aneurysmf) Pericardial Cystg) Morgagni Herniah) Sternal Tumorsi) Pericardial Fat Pad

-The anterior mediastinum is that portion of the mediastinum anterior to the pericardium and below the level of the clavicles

-It includes the thymus , lymph nodes and may contain the portions of a retrosternal thyroid

a) Thymus Abnormalities :1-Thymoma2-Thymolipoma3-Benign Thymic Hyperplasia4-Thymic Cyst

-On frontal chest radiographs in infants and young children , the thymus is strikingly large but difficult to discriminate from the cardiac silhouette

-The thymus usually has smooth borders and remains visible on radiographs through the age of 3 years

-The thymic wave sign , a scalloped or wavy contour of the organ is created by the impression of the anterior reflection of the ribs

-The thymic sail sign , a triangular slightly convex right lobe of the thymus with a sharply demarcated base caused by the minor fissure

-Typically , the thymus is visible at CT and fills the perivascular space throughout the first 2 decades of life

-In children younger than 5 years , it typically appears quadrilateral with convex borders

-As children grow , the thymus gradually becomes triangular with straight or concave border

1-Thymoma :a) Incidenceb) Associationsc) Pathologyd) Radiographic Features

a) Incidence :-Thymoma is the most common anterior

mediastinal tumor in the adult (very rare in children)

b) Associations :1-Myasthenia Gravis (35% of thymoma

patients have myasthenia gravis)2-Aplastic Anemia (50% have thymoma)3-Hypogammaglobulinemia4-Red cell Aplasia

c) Pathology :1-Benign Thymoma, 75% :-Common in patients with myasthenia2-Malignant Thymoma , 25% :-Local spread into pleura but no

hematogenous metastases-More common in patients without

myasthenia

d) Radiographic Features :1-Plain Radiography2-CT

1-Plain Radiography :-Presents as an anterior mediastinal mass-Seen as a well defined lobulated soft tissue

density slightly towards one side of the mediastinum

-Can demonstrate associated calcification (commonly amorphous / flocculent)

2-CT :-Anterior mediastinal soft tissue mass :1-Asymmetrical location on one side2-Homogeneous density and signal intensity3-Some have cystic components (40% of the cases and are

mostly focal)4-Contrast medium enhancement5-Invasive thymomas show growth through capsule into

adjacent tissue , drop metastases into pleural space are common

6-Calcification , 20 %

CT shows anterior mediastinal masses with coarse calcifications (A) and a circular peripheral calcification (B)

Cystic thymoma ,  CT+C shows a low attenuation lesion (arrow) in the anterior mediastinum

Invasive thymoma with pleural metastases

Axial contrast-enhanced CT images showing a left anterior mediastinal mass (arrows in a) associated with a left parietal pleural nodule (arrow in b) and left diaphragmatic pleural nodules (arrows in c), apperances are those of invasive thymoma with pleural «drop metastases»

Thymoma with no signs of mediastinal fat invasion (A, arrows) , one year after surgery , pleural metastasis was found (B, arrow)

2-Thymolipoma :a) Incidenceb) Associationsc) Pathologyd) Radiographic Features

a) Incidence :-Is a rare benign anterior mediastinal

mass of thymic origin-Comprises 2-9% of all thymic neoplasms-Mean age of 22 years-Tumors usually grow to large sizes (75%

are >500 g) with few or no symptoms

b) Associations :1-Myasthenia Gravis (in 3 % of thymolipoma)2-Aplastic Anemia3-Hypogammaglobulinemia4-Grave’s Disease

c) Pathology :-Thymolipomas are composed of a mixture mature

adipose tissue with islands of thiymic tissue

d) Radiographic Features :1-Plain Radiography2-CT

1-Plain Radiography :-Typically these tumors appear as

large anterior mediastinal masses-The larger tumors tend to hang down one

or either side of the pericardium and being soft , they mold themselves to the adjacent mediastinum and diaphragm and often mimic cardiomegaly

Thymolipoma : a) Chest radiograph showing a widening of the cardiac silhouette , b) CT confirms the presence of a heterogeneous mass with fatty components growing in caudal direction

2-CT :-On CT thymolipomas typically appears

almost entirely fatty with some areas of inhomogeneous soft tissue density that represent thymic tissue

CT show a large and well defined mass (arrows) that has extensive fat content and contains small amounts of thin fibrous septa

3-Benign Thymic Hyperplasia :a) Pathologyb) Causesc) Radiographic Features

a) Pathology :-It can be subdivided into two forms :1-True Thymic Hyperplasia2-Lymphoid Hyperplasia

b) Causes :1-True Thymic Hyperplasia :a) Rebound hyperplasia to chemotherapy ,

thymic rebound hyperplasia (3 to 10 months after the start of chemotherapy)

b) Radiation Therapyc) Burnsd) Other Severe Systemic Stresses (e.g.

pneumonia)

2-Lymphoid Hyperplasia :a) Myaesthenia Gravisb) SLEc) Rheumatoid Arthritisd) Sclerodermae) Graves Disease

c) Radiographic Features :-Diffuse symmetric enlargement of the gland is

the key morphologic feature of hyperplasia (neoplasm tends to manifest as a focal mass)

-Size and morphology of normal thymus : >20 years of age : <13 mm>30 years of age : Convex margins are abnormal-No increase in size over time

Thymic rebound hyperplasia in an 18 month old girl recovering from pneumonia(a) Frontal chest radiograph shows air trapping and bilateral perihilar peribronchial infiltrates (arrows) ,

findings consistent with viral pneumonia(b) Follow-up radiograph shows thymic rebound hyperplasia (arrowheads) and resolution of the pneumonic

infiltrates (arrows)

Thymic rebound hyperplasia in an 11 year old girl with Hodgkin lymphoma(a) CTC shows right sided mediastinal adenopathy (arrow) , Arrowhead = thymus(b) CT scan obtained after completion of chemotherapy shows regression of the

adenopathy (arrow) , there is early thymic rebound hyperplasia (arrowhead)(c) CT scan obtained 1 month after chemotherapy shows that the nodal mass has almost

resolved (arrow) and the thymic rebound hyperplasia is nearly complete (arrowhead)

Dramatic thymic rebound hyperplasia in a 14 year old boy who completed chemotherapy for primary mediastinal T-cell lymphoma 6 months earlier

4-Thymic Cyst :a) Causesb) Radiographic Features

a) Causes :1-Congenital :-Contains thymic tissue in wall : often unilocular2-Acquired : often multiloculara) Secondary to thoracotomyb) Following chemotherapy or radiotherapy for

mediastinal malignancyc) Inflammatory

b) Radiographic Features :1-Plain Radiography2-CT

1-Plain Radiography :-Thymic cysts usually appear as

homogeneous circumscribed masses that may have calcified rims

2-CT :-Thin walls and no solid component and

show no contrast enhancement

CT+C shows inhomogenous unilocular low attenuation mass (arrows) in the anterior mediastinum

A well marginated mass with a homogeneous attenuation usually in the range of water attenuation (0–20 HU) and without an enhancement of the wall or infiltrative appearance

Cystic changes of the thymus and lymph nodes at diagnosis in a 19 year old man with Hodgkin lymphoma , CT+C shows a solid (arrow in a) and cystic (arrows in b) thymic mass , by the time the patient completed chemotherapy , the cystic nodes had resolved but the cystic areas in the thymus remained unchanged

Cystic change of the thymus in a 28 year old man with Hodgkin lymphoma treated 3 years earlier , CT+C shows a thymic cyst (arrow) and thymic rebound hyperplasia (arrowhead)

b) Thyroid Masses :1-Incidence2-Radiographic Features

1-Incidence :-Thyroid masses that extend into the

mediastinum : goiter > adenoma , carcinoma , lymphoma

2-Radiographic Features :a) Plain Radiographyb) CT

a) Plain Radiography :-Tracheal displacement is the most common

finding by CXR

CXR of a partial substernal goiter compressing the trachea from the right side

b) CT :-Mass is contiguous with cervical thyroid and is

well defined -Heterogeneous density by CT : calcium , iodine

(70 to 120 HU) , colloid cysts-Marked and prolonged contrast enhancement-They don’t usually project below the arch of the

aorta (differentiating them from thymomas and teratoma)

-Nuclear scan with either 99mTc or 123I confirms the diagnosis

Frontal (a) view of the chest radiograph shows an opacity on the right side of the trachea (arrow), which appears shifted contralaterally and reduced in caliber, unenhanced CT scans (b-d) demostrate a heterogenous mass which goes down into the anterior mediastinum referred to a goiter

Substernal Thyroid Goiter , CT+C of the chest shows a large contrast enhancing mass in the anterior mediastinal containing calcifications and areas of necrosis

CT of a partial substernal goiter compressing the trachea from the left side

c) Mediastinal Lymphoma :1-Incidence2-Pathology3-Radiographic Features

1-Incidence :-Lymphomas are responsible for 45%

of anterior mediastinal masses in children-Only 10% of lymphomas which involve the

mediastinum are primary (i.e. mediastinum involvement not part of systemic disease) and the majority are Hodgkin lymphomas (50-70%)

2-Pathology :a) Hodgkin Lymphoma :1-Lymphocyte Predominant (LP) , <5 %2-Nodular Sclerosing (NS) , 70%3-Mixed Cellularity (MC) , 25%4-Lymphocyte Depleted (LD) , <5% b) B-Cell Neoplasmsc) T-Cell Neoplasms

-Primary mediastinal lymphomas are most frequently of 3 histologic varieties :

1-Nodular Sclerosing Hodgkin lymphoma2-Primary mediastinal large B-cell

lymphoma3-Lymphoblastic Lymphoma (T-cell)

3-Radiographic Features :a) Plain Radiographyb) CT

a) Plain Radiography :-A soft tissue mass may be clearly visible or more

frequently the mediastinum is widened and the retrosternal airspace is obscured

-The hilum overlay sign refers to an appearance on frontal chest radiographs of patients with a mass projected at the level of the hilum which is in fact either anterior or posterior to the hilum , when a mass arises from the hilum, the pulmonary vessels are in contact with the mass and as such their silhouette is obliterated , the ability to see the edges of the vessels through the mass implies that the mass is not contacting the hilum and is therefore either anterior or posterior to it , most of these masses are found to be in the anterior mediastinum

Normal Obliteration of the retrosternal space in mediastinal lymphoma

Hilum Overlay Sign

b) CT :-Soft tissue attenuating mass with smooth or

lobulated margins which conforms to surrounding structures (prevascular , paratracheal) involvement

-Other features include :1-Parenchymal invasion , uncommon2-Pleural effusion3-Pericardial effusion4-Chest wall invasion

-Calcification is usually seen following therapy and can have varying morphology including irregular , diffuse or even egg shell

-Lymphomas have areas of necrosis but they usually do not have cystic areas , thymic cysts can occur after irradiation of mediastinal lymphomas or chemotherapy

Large soft tissue mass in the anterior mediastinum which arises in the thymus , there is associated paratracheal adenopathy (arrow)

Anterior mediastinal mass with bilateral pleural effusion

28 year old woman with Hodgkin disease , chest radiograph shows an anterior mediastinal mass (A, arrow) which on axial CT is irregular and shows areas of necrosis (B, arrows)

d) Germ Cell Tumors :1-Incidence2-Pathology3-Radiographic Features4-Differential Diagnosis

1-Incidence :-Germ cell tumors are the most common

cause of a fat containing lesions in the anterior mediastinum and the second most common cause of an anterior mediastinal mass in children

2-Pathology :-Tumors arise from rests of primitive cells and are

of variable malignant potential (SECTE)a) Seminomab) Embryonal cell carcinomac) Choriocarcinomad) Teratoma (70% of germ cell tumors) ,

teratocarcinomae) Endodermal sinus tumors (yolk sac tumors)

3-Radiographic Features :a) Plain Radiographyb) CT

a) Plain Radiography :-Anterior mediastinal mass +/- areas of

calcifications

Teratoma in a 39 year old man , PA chest film shows an anterior mediastinal mass (A, arrows) , CT shows a large area of fat within the mass (B, arrow)

b) CT :-Benign teratoma (90%) is a well defined thick wall

cystic mass containing a variable mixture of :Calcification , 30%Fat , fat-fluid levelsCystic areasSoft tissue-Mature teratoma can be very large and still be benign-Malignant teratoma (10%) tends to have irregular or

nodular walls and a predominance of soft tissue components , may show pulmonary or liver metastases and chest wall invasion

Extensive mediastinal involvement (A,B, white arrows) , cystic upper mediastinal mass (A,B red arrows) , immature tooth (B, yellow arrow)

42 year old man with a teratoma , note the coarse calcifications (A,B, white arrows) and areas of fat attenuation measuring -103 HU (A,B, red arrows)

CT+C shows large septated anterior mediastinal mass containing fat and bony elements

CT+C shows an anterior mediastinal mass containing calcification (black arrow) , fat (white arrow) and soft tissue components (dotted white arrow)

Benign Teratoma

Benign Teratoma

Malignant Teratoma

4-Differential Diagnosis :-From Mediastinal Masses Containing Fata) Teratodermoidb) Diaphragmatic Herniac) Lipomad) Liposarcomae) Thymolipomaf) Mediastinal Lipomatosisg) Hamartomah) Chylolymphatic Cyst

e) Thoracic Aortic Aneurysm :1-Incidence2-Pathology3-Radiographic Features

1-Incidence :-Are relatively uncommon compared to

abdominal aortic aneurysm

2-Pathology :-Thoracic aortic aneurysms can be divided

pathologically according to their relationship to the aortic wall :

a) True Aneurysm :1-Atherosclerotic aneurysms (most common)2-Inflammatory / Aortitis :-R.A. , Ankylosing Spondylitis , Giant cell Arteritis

& Syphilis

3-Structural : Cystic media necrosis-Marfan disease-Ehlers-Danlos syndromeb) False Aneurysm :-Trauma-Mycotic aneurysm

3-Radiographic Features :a) Plain Radiographyb) CT

a) Plain Radiography :-The thoracic aorta can usually be seen on

both frontal and lateral chest radiographs and aneurysms are often obvious

-Mural calcification is seen both in atherosclerotic disease as well as various causes of aortitis

b) CT :-CTA is the work horse of aneurysm assessment-Typically aneurysms appear as dilatations of the

lumen , the walls may be thin or thickened by presence of mural thrombus (circumferential or more frequently eccentric)

-Calcified atherosclerotic disease is often identified not only in the wall of the aneurysm but in adjacent arteries

-If rupture or leak has occurred hematoma / fluid may be seen adjacent to the aorta , in the left pleural cavity or in the pericardium

Dissecting Aoritc Aneurysm

f) Pericardial Cyst :1-Incidence2-Location3-Radiographic Features4-Differential Diagnosis

1-Incidence :-Uncommon benign congenital anomaly of

the anterior mediastinum -Incidental findings in asymptomatic patients

, usually after age 30

2-Location :-Found in the right anterior cardiophrenic

angle but can be found almost anywhere adjacent to the heart

3-Radiographic Features :a) Plain Radiographyb) CT

a) Plain Radiography :-Well defined round or oval masses located

in the normally clear cardiophrenic angle

b) CT :-Usually appears as a well defined non-

enhancing low (water) attenuating rounded mass next to the pericardium

Typical benign pericardial cyst with serous content in a 46-year-old woman, (a) Coronal T1 shows a round low-signal-intensity cyst with a regular thin wall, (b) T2 shows a homogeneous high-signal-intensity cyst without septation or a mural nodule

4-Differential Diagnosis : From cystic mediastinal mass :1-Congenital :a) Bronchogenic cyst , usually subcarinal or right

paratracheal siteb) Enteric cyst , paraoesophageal sitec) Neuroenteric cyst , associated anomaly of spine2-Pericardial cyst , usually cardiophrenic angle3-Thymic cyst , can develop following radiotherapy for

Hodgkin’s disease4-Cystic tumors :a) Lymphangiomab) Teratomac) Teratodermoid5-Pancreatic pseudocyst , can track up into mediastinum6-Meningocele , 75% association with NF7-Chronic abscess8-Old hematoma

g) Morgagni Hernia :-See Congenital Pulmonary Lesions

Morgagni hernia in a 2 year old child , lateral chest radiograph shows herniation of a bowel loop (arrows) in a classic location through an anteromedial defect

h) Sternal Tumors :-Metastases are the most common (breast ,

bronchus , kidney & thyroid)-Malignant primary tumors (chondrosarcoma

, myeloma , reticulum cell sarcoma and lymphoma) are more common than benign (chondroma , Aneurysmal bone cyst and Giant cell tumor)

i) Pericardial Fat Pad :-Especially in obese people-A triangular opacity in the cardiophrenic

angle on the PA view-It appears less dense than expected

because of the fat content

Epicardial fat pad , (a) PA chest radiograph shows loss of the cardiac silhouette at the border of the right side of the heart and an epicardial fat pad with relatively low density (arrow) , (b) CT scan shows the fat pad (arrow) as an area of homogeneous fat attenuation adjacent to the right border of the heart

-Differential Diagnosis : Cardiophrenic angle lesions

1-Pericardial fat pad2-Pericardial cyst3-Pericardial fat necrosis4-Morgagni’s hernia5-Lymphadenopathy : metastases , lymphoma6-Pericardial lipomatosis

2-Middle Mediastinal Masses : (A+B)1-Adenopathy2-Aortic Aneurysm3-Bronchogenic Cyst4-Carcinoma of the Bronchus

1-Adenopathy :-The paratracheal , bronchopulmonary and / or

subcarinal nodes may be enlarged-This may be due to :a) Neoplasm (Lymphoma , Leukemia & Mets)b) Infection (most commonly T.B. , Histoplasmosis

or coccidiodomycosis)c) Sarcoidosisd) Hyperplasia (Castleman’s disease)

a) Neoplasm (Lymphoma , Leukemia & Mets) :-See Lung neoplasms

b) Infection (most commonly T.B. , Histoplasmosis or coccidiodomycosis) :

-See Pulmonary Infections

c) Sarcoidosis :-See Diffuse Lung Lesions

PA chest radiograph shows the right paratracheal stripe (arrow) , the azygos vein is seen at the inferior margin of the stripe at the tracheobronchial angle (arrowhead) , (b) CT 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 (arrow) , these interfaces create the right paratracheal stripe , note the position of the SVC (arrowhead) which explains why the paratracheal stripe is seen projecting through the SVC at radiography , (c) CT obtained at the level of the azygos arch shows that the azygos vein (arrow) disrupts the lung tracheal wall interface at the tracheobronchial angle

Lymphadenopathy , (a) PA chest radiograph , the right paratracheal stripe is not seen having been obliterated by a right paratracheal mass (arrowheads) , (b) CT shows right paratracheal lymphadenopathy (arrow) which obliterates the air soft tissue interface between the right lung and the tracheal wall , this finding explains the obliteration of the right paratracheal stripe in a

PA chest radiograph , the AP window reflection (arrowhead) extends from the aortic knob to the left pulmonary artery and has a normal concave appearance , the aortic pulmonary reflection (arrow) is a more anterior line and extends from the aortic arch to the level of the left main bronchus

AP window lymphadenopathy , (a) Chest radiograph shows the AP window with an abnormal convex border (arrow) , (b) CT shows lymphadenopathy (arrow) which accounts for the distortion of the AP window in a

Paratracheal lymph node enlargement in metastatic carcinoma

Frontal Chest X-ray (a,b) shows a slightly convex border of the aortopulmonary window (arrow) suspicious for the presence of a mass in the middle mediastinum, CT scan shows enlarged lymphnodes in the aortopulmonary window (arrow), causing the abnormality seen on chest radiography, it was a lymphoma in a 11-year-old-girl

Paratracheal and aortopulmonary window lymph node enlargement

Subcarinal lymph node enlargement in CLL

Frontal (a) and lateral (b) chest X-ray show a bilateral hilar enlargement, more evident on the right, CT+C (c,d) showing bilateral hilar lymph nodes in patient with sarcoidosis

d) Giant Benign Lymph Node Hyperplasia (Castleman’s disease) :

1-Incidence2-Pathology3-Radiographic Features

1-Incidence :-Rare-Age < 30 years -Large benign mediastinal lymph node

masses-Etiology is unknown (nodal hyperplasia vs

benign tumor)

2-Pathology :-Two histologic types :a) Hyaline vascular , 90%b) Plasma cell , 10%

3-Radiographic Features :-Bulky mediastinal mass lesion (3 to 12 cm) :

anterior > middle > posterior mediastinum-Dense homogeneous contrast enhancement is

the key feature (vascular lesions)-On CT, 5% to 10% of Castleman disease showed

intralesional calcifications, typically being discrete in morphology

-Dynamic CT demonstrates early rapid enhancement with washout in the delayed phase

PA chest Radiograph shows widening of upper mediastinum , aortopulmonary and azygos adenopathy and enlargement of hila (arrows) with extension of lesion below right hilum

Unenhanced CT using bone window setting reveals posterior mediastinal mass (arrow) with typical arborizing pattern of intralesional calcifications

CT+C shows matted lymphadenopathy (arrows) formed by confluence of inhomogeneously enhancing enlarged lymph nodes confined to anterior mediastinum

2-Aortic Aneurysm :-See before

Aneurysm of the aortic arch. (a) PA chest radiograph shows the AP window with a convex border (arrow) , (b) CT reveals an aneurysm (arrow) arising laterally from the aortic arch , a finding that accounts for the abnormality seen in a

3-Bronchogenic Cyst :-See Congenital Pulmonary lesions

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

CT+C : well circumscribed unilocular water attenuation cyst in the middle mediastinum , the cyst has smooth imperceptible walls with no enhancement

Bronchogenic cyst , CT shows a subcarinal mass with fluid density

CT Scanogram (a) shows an oval, huge, mass (arrows) that cause a widening and distortion of azygoesophageal recess, coronal (b) and sagittal (c) MPR reconstruction demonstrate a cyst with uniform water attenuation and with an imperceptible wall, this was a bronchogenic cyst

Bronchogenic cyst in a 49-year-old man with a 2-week history of fever and cough, (a) Chest radiograph shows a round mass (arrow) that displaces the right primary bronchus superiorly, as well as pneumonia of the middle lobe and pleural effusion, (b) Contrast material-enhanced CT scan shows a cyst with uniform water attenuation and with an imperceptible wall.

Bronchogenic cyst in a 44-year-old woman with a 3-year history of chest pain, CT scan shows a thin-walled water-attenuation cyst in the posterior mediastinum (arrow)

4-Carcinoma of the Bronchus :-See Pulmonary Tumors

a) A 55 yr old dyspnoeic female , chest radiograph shows widened mediastinum particularly on the right with reduced vascularity of the right lung

b) CT+C shows central mediastinal mass invading the right pulmonary artery , small cell carcinoma was confirmed on percutaneous biopsy

3-Posterior Mediastinal Masses (ACTH)1-Posterior Mediastinal Neural Tumors2-Extrameduallary Hematopoiesis3-Paraspinal Abscess4-Descending Aortic Aneurysm5-Oesophageal Duplication Cyst6-Neuroenteric Cyst7-Pancreatic Pseudocyst8-Bochdalek Hernia9-Hiatus Hernia10-Lateral Meningocele

1-Posterior Mediastinal Neural Tumors :a) Incidenceb) Peripheral Nerve Sheath Tumorc) Sympathetic Ganglia Tumorsd) Paraganglioma

a) Incidence :-Neurogenic tumors are the cause ofapproximately 90% of posterior mediastinalmasses-They can be subdivided into three groups by theirlocation and involvement of peripheral nerves or sympathetic chain :1-Peripheral Nerve Sheath Tumors2-Sympathetic Ganglia Tumors3-Paraganglioma-Peripheral nerve sheath tumors and paragangliomas

are far more common in adults while the sympathetic ganglia tumors are commoner in children

b) Peripheral Nerve Sheath Tumor :1-Incidence2-Schwannoma3-Neurofibroma4-Malignant Peripheral Nerve Sheath

Tumors

1-Incidence :-These tumors manifest as round paravertebral

masses that span one or two vertebral bodies-They are homogenous soft tissue attenuation

masses at CT and the commonest cause of posterior mediastinal and paravertebral masses

-They may cause widening of the neural foramen and thickening of the adjacent posterior rib

2-Schwannoma :a) Incidenceb) Locationc) Radiographic Features

a) Incidence :-Are benign tumors of schwann cell origin

and are the most common tumor of peripheral nerves

-Peak presentation is in the 5th-6th decades-When they occur in patients with

neurofibromatosis type 2 (NF2) schwannomas usually present by the 3rd decade

b) Location :-Arise posteriorly , frequently in neural

foramina

1-Vertebral Body2-Neural Foramen3-Articular Pillar4-Lamina5-Spinous Process

c) Radiographic Features :1-Plain Radiography2-CT3-MRI

1-Plain Radiography :-Both benign and malignant tumors may erode ribs-They may enlarge the neural foramina (dumbbell

shaped lesion)-Scalloping of posterior vertebral bodies may occur-They may produce a scoliosis-Pleural effusion may occur with benign as well

as malignant neural tumor

There is an opacity in the left posterior mediastinum , there is associated widening of the 4th intercostal space posteriorly with scalloping of the inferior margin of the 4th rib , there is also some coarse calcification within the lesion

Cervical X-Ray (a-b) demonstrate a marginated and round opacity (white arrows), with disrupting of left paravertebral stripe, CT scan (c) confirms a left hypodense and homogeneous paravertebral mass, this mass revealed features consistent with schwannoma

2-CT :-Isodense round or oval mass , <2 vertebral

bodies long-Dense contrast enhancement :Small tumors show homogeneous

enhancementLarger tumors may show heterogeneous

enhancement

CT+C

3-MRI :*T1 : 70% hypointense , 30% isointense*T2 : Very hyperintense , may show small

internal low signal foci (calcification) and areas of necrosis

*T1+C : Dense enhancement : -Homogeneous if small-Heterogeneous if large

T1

T2

Coronal T2 shows well defined paravertebral mass with peripheral high signal intensity and relatively low signal intensity centrally , mass has peripheral low signal intensity rim (arrows) that reflects tumor capsule

Axial T2 shows well defined mass with heterogeneous high signal intensity in right paravertebral region , mass protrudes toward adjacent right neural foramen (arrow) and shows “dumbbell” configuration , mass has low signal intensity rim (arrowhead) in periphery

Axial T1+C shows heterogeneous enhancement that is relatively strong in center of mass

T1+C

T1

T2

T1+C

A, Coronal T2 shows well-defined mass in right paravertebral region , mass has very high signal intensity area (arrow) in center and low signal intensity rim (arrowhead) in periphery

B, Coronal T1+C fat-suppressed shows no enhancement of central area (arrow) which reflects cystic change in mass

3-Neurofibroma :a) Incidenceb) Locationc) Radiographic Features

a) Incidence :-Are benign peripheral nerve sheath tumors -Peak presentation is between 20 and 30

years of age-The majority of neurofibromas are solitary

and sporadic , however there is an association with NF1

b) Location :-Arise posteriorly , frequently in neural

foramina

c) Radiographic Features :1-Plain Radiography2-CT3-MRI

1-Plain Radiography :-Both benign and malignant tumors may erode ribs-They may enlarge the neural foramina (dumbbell

shaped lesion)-Scalloping of posterior vertebral bodies may occur-They may produce a scoliosis-Pleural effusion may occur with benign as well

as malignant neural tumor

Neurofibroma (red arrow) , multiple subcutaneous neurofibromas (yellow arrows)

Posterior scalloping of lumbar vertebral bodies in NF

2-CT :-Well defined hypodense mass-Minimal or no contrast enhancement

Rib notching with Dumbbell-shaped Neurofibroma

3-MRI :*T1 :-Hypointense*T2 :-Hyperintense-A hyperintense rim and central area of low signal

resulting in a target sign may be seen due to a dense central area of collagenous stroma

*T1+C :-Heterogenous enhancement

T1+C , dumbbell shaped neurofibroma with intra and extraspinal extension , note the displacement of the adjacent thoracic cord (arrow)

Axial T2 shows well defined mass with homogeneous high signal intensity in left paravertebral region , mass has thin low signal intensity rim (arrows) in periphery

Target sign in Neurofibroma

4-Malignant Peripheral Nerve Sheath Tumors (MPNST) :

-Are malignant forms of neurofibromas and schwannomas 

-Associated with NF1-Imaging criteria are generally considered

unreliable in differentiating from a more benign neurofibroma or schwannoma

c) Sympathetic Ganglia Tumors :1-Incidence2-Neuroblastoma3-Ganglioneuroma4-Ganglioneuroblastoma

1-Incidence :-These tumors tend to present as elongated paraspinal

masses that span multiple vertebral levels-Intratumoural calcification is common-They are :a) Neuroblastoma : young childrenb) Ganglioneuroma : children and adultsc) Ganglioneuroblastoma : older children-Neuroblastoma and ganglioneuroblastoma are most

commonly seen in children and in a child they comprise the commonest neurogenic tumor

2-Neuroblastoma :a) Incidenceb) Locationc) Radiographic Features

a) Incidence :-Is a tumor of neuroblastic origin and the most

common extracranial solid childhood malignancies and the third commonest childhood tumor after leukemia and brain malignancies

-The tumors typically occur in infants and very young children (mean age of presentation being 22 months) with 95% of cases diagnosed before the age of 10 years

b) Location :-Neuroblastomas arise from the sympathetic

nervous system-Posterior mediastinum : 20%

c) Radiographic Features :1-Plain Radiography2-CT3-MRI

1-Plain Radiography :-Appearances are non-specific , typically

shows an intrathoracic soft tissue mass-Pressure on adjacent bones may cause

remodeling of ribs , vertebral bodies or pedicle thinning

-Up to 30% may have evidence of calcification on the plain film

Homogenous opacity lesion in the right upper and mid zone with broad base towards mediastinum , the lesion is causing shift of mediastinum and trachea to the contralateral side and compressing the trachea just above the carina (arrow head) , the lesion is extending above the clavicle (cervico-thoracic sign) and erosion of posterior end of third and fourth ribs (Long arrow)

*N.B. : Cervico-thoracic sign-A variant of the silhouette sign-It helps to discern the anterior or posterior location of mass

in the superior mediastinum on frontal chest radiographs-As the anterior mediastinum ends at the level of

the clavicles and as such the upper border an anterior mediastinal lesions cannot be visualized extending above the clavicles

-Any lesions with a discernible upper border above that level must be located posteriorly in the chest ; i.e. apical segments of upper lobes , pleura or posterior mediastinum

2-CT :-The tumor typically is heterogeneous with calcifications

seen in 80 - 90% of cases-Areas of necrosis are of low attenuation-The morphology of is often most helpful with the mass

seen insinuating itself beneath the aorta and lifting it off the vertebral column , it tends to encase vessels and may lead to compression , adjacent organs are usually displaced

-Lymph node enlargement is often present -Calcification in a posterior mediastinal mass points to a

neural tumor in a kid rather than a met from somewhere else

Heterogeneously enhancing mass lesion in the right posterior mediastinum extending to middle mediastinum causing compression of the trachea , the lesion is showing multiple small foci of calcification (black arrows)

3-MRI :*T1 :- Heterogeneous and iso to hypointense*T2 :-Heterogeneous and hyperintense-cystic / necrotic areas very high intensity*T1+C :-Variable and heterogeneous enhancement

1 month old boy with mediastinal neuroblastoma , coronal T2 shows long vertically oriented mass with homogeneous high signal intensity and tapering appearance in left paravertebral region , invasion of vertebrae is not seen

Axial T2 in a patient with a thoracic neuroblastoma shows a large right posterior mediastinal mass extending into the spinal canal and displacing the cord laterally to the left , the mass is hyperintense on T2

T1+C shows inhomogeneous enhancement of the mass which appears to have a component arising from the neural foramen (white arrow)

3-Ganglioneuroma :a) Incidenceb) Locationc) Radiographic Features

a) Incidence :-They tend to occur in the pediatric

population and are often asymptomatic-Usually , patients are older than 10 years

old , compared to neuroblastoma which occurs in patient younger than 3 years old

b) Location :-Can potentially occur anywhere along the

peripheral autonomic ganglion sites , the posterior mediastinum one of the commonest locations (40%)

c) Radiographic Features :1-Plain Radiography2-CT3-MRI

1-Plain Radiography :-All neuroblastic tumors (i.e.

ganglioneuroblastomas , ganglioneuromas and neuroblastomas) look similar

-See Neuroblastoma

Chest radiograph shows a right paraspinal well-defined density in the retrocardiac region , the right cardiophrenic angle appears normal

2-CT :-Typically seen as well circumscribed solid

encapsulated masses-Tend to be iso to hypoattenuating to muscle-May demonstrate calcifications (40%)-Delayed heterogeneous uptake of contrast 

Paraspinal Ganglioneuroma, non-enhanced Axial CT scan reveals a paraspinal homogeneous low attenuation fusiform mass which after resection proved to be a ganglioneuroma

3-MRI :*T1 :-Homogeneously low or intermediate signal*T2 :-Heterogenously intermediate or high signal*T1+C :-Ranging from none to heterogenous

enhancement

(a) Chest radiography shows an oblong mass in the right paraspinal region , the lateral margins of the mass are indistinct & there is RT lower lobe pneumonia , (b) CT+C shows that the mass is heterogenous and contains calcifications (c) T2 shows that the mass is of high signal intensity

Coronal T2 shows long vertically oriented mass with heterogeneous high signal intensity and tapering appearance in left paravertebral region

, Coronal T1+C shows heterogeneous enhancement in mass.

T1+C of a ganglioneuroma shows homogeneous enhancement of the lesion , the lesion is extending from the right paraspinal region into the epidural space through the neural foramina causing cord compression

T1 of a ganglioneuroma , the sagittal views shows a well-defined solid mass located slightly anterior to the midthoracic vertebral bodies , the mass extends into and widening multiple neural foramina , flow voids within the lesion represents vascularity

4-Ganglioneuroblastoma :a) Incidenceb) Locationc) Radiographic Features

a) Incidence :-Uncommon peripheral neuroblastic tumor- Most commonly in babies and in young

children -Ganglioneuroblastoma have intermediate

malignant potential between that of neuroblastomas and ganglioneuromas

b) Location :-Can potentially occur anywhere along the

peripheral autonomic ganglion sites , the posterior mediastinum one of the commonest locations

c) Radiographic Features :1-Plain Radiography2-CT3-MRI

1-Plain Radiography :-See Neuroblastoma

2-CT :-See Ganglioneuroma + areas of bleeding

and necrosis may be as large as 4 cm and appear to be of lower attenuation

CT without contrast of a ganglioneuroblastoma demonstrates a large left heterogeneous paraspinal lesion with speckled calcifications that are predominantly peripheral , the mass is displacing the mediastinum to the right

3-MRI :-See Ganglioneuroma + areas of hemorrhage

have a high T1 signal intensity and cystic areas have a high T2 signal intensity

-Ganglioneuroblastomas , like neuroblastomas and other malignant tumors have an enhancing pattern of early enhancement followed by a partial washout , early enhancement is indicative of high vascularity

Axial T1 shows high signal intensity areas (arrowheads) that suggest hemorrhage in center of mass

Axial T1+C shows heterogeneous enhancement in mass , enhancement is not seen in center of mass (arrowheads) and tumor necrosis is suspected

MRI scan showing homogenous soft tissue density mass in the posterior mediastinum

d) Paraganglioma :1-Incidence2-Location3-Radiographic Features

1-Incidence :-Rare tumors derived from chromaffin cells

(neuroectodermal cells) associated with sympathetic ganglion of the autonomic nervous system

-Paraganglioma (= chemodectoma , histologically similar to pheochromocytoma) : functional tumors , may secrete catecholamines

2-Location :-They can arise from two major cluster of

sympathetic ganglion cells :a) Paraaortic (aorticopulmonary)b) Paravetebral(aorticosympathetic) location

-Normal anatomy of mediastinal nervous tissues

-Most peripheral nerve tumors originate from spinal or proximal intercostal nerve in posterior mediastinum

-Thoracic sympathetic trunks and their associated ganglia are located on side of vertebral bodies

-Aortosympathetic paraganglia are adjacent to sympathetic chain in posterior mediastinum whereas aortopulmonary paraganglia are located along great vessels

3-Radiographic Features :a) Plain Radiographyb) CTc) MRI

a) Plain Radiography :-Well circumscribed rounded mediastinal

mass

29 year old man with posterior mediastinal paraganglioma , chest radiograph shows large lobulated mass in left paraspinal area (arrow)

b) CT :-Mediastinal paragangliomas are seen in as a

mass in a characteristic location in the paraaortic region of the middle mediastinum or paravetebral region of the posterior mediastinum corresponding to major cluster of sympathetic ganglion cells

-Uncomplicated mediastinal paragangliomas demonstrate intense contrast enhancement

29 year old man with posterior mediastinal paraganglioma , CT+C shows hyperenhancing mass with cystic change (arrowhead) in left posterior mediastinum

29 year old man with posterior mediastinal paraganglioma , CT shows  linear and punctate foci of calcification (arrow) within tumor mass

Axial CT+C shows heterogeneous mass between ascending aorta and pulmonary trunk , there are intratumoral vessels (arrows), which suggest hypervascularity of tumor , pulmonary trunk is compressed by mass and invasion is suspected

c) MRI :-Mediastinal paraganglioma shows

enhancement on T1+C with conspicuity of the lesion hightlighted by flow avoid in the adjacent mediastinal vessels on spin-echo sequences

Axial T2 fat-suppressed shows heterogeneous high signal intensity in mass and flow voids (arrows) that reflect high flow in intratumoral vessels

2-Extrameduallary Hematopoiesis :a) Causesb) Radiographic Features

a) Causes :-Is a response to erythropoiesis failure in bone

marrow :1-Myeloproliferative Disorders :-CML-Polycythemia Vera2-Haemoglobinopathies :-Sickle cell disease3-Thalassemia

b) Radiographic Features :-Posterior mediastinal masses , these are

paraspinal masses that may be unilateral or bilateral and have smooth sharply delineated often lobulated margins

-Suspect diagnosis if :1-Multiple bilateral posterior mediastinal masses2-Cortical bone changes by CT3-Clinical history of anemia4-Marked contrast enhancement

Left : There are large paraspinal masses (white arrows) with smoothly marginated lobulated contours , all of the ribs (red arrow) are expanded and the overall bone density is increased

Right : Large paraspinal masses are seen (white arrows)

Large lobulated retrocardiac masses

Frontal chest film (a) and scout view (b) show a bulging of the right paraspinal line, CT scans (c-f) show bilateral soft-tissue paraspinal masses, representing extramedullary hematopoiesis, in a young thalassaemic patient

3-Paraspinal Abscess :a) Causesb) Radiographic Features

a) Causes :-Infection of the soft tissues surrounding the

spine due to a suppurative bacterial or mycobacterial infection with phlegmon formation

b) Radiographic Features :-High signal intensity fluid collections on T2-Peripheral enhancement in areas of

reactive granulation tissue on post contrast

-May be associated with intervertebral disc space infection

-Tubercular abscesses may eventually calcify

PA chest radiograph , the left paraspinal line (arrow) is seen separate and distinct from the vertebral body (black arrowhead) and the descending thoracic aorta (white arrowhead)

CT 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

PA radiograph shows the right paraspinal line (arrow)

Paraspinal abscess , (a) PA 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) , (b) CT 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 wall

4-Descending Aortic Aneurysm :-See before

Descending aortic aneurysm , (a) PA chest radiograph shows lateral displacement of the lateral margin of the descending thoracic aorta due to an aortic aneurysm (arrowheads) , (b) CT also demonstrates the aneurysm (arrow)

5-Esophageal Duplication Cyst :-See Congenital Pulmonary Lesions

6-Neuroenteric Cyst :-See Congenital Pulmonary Lesions

Duplication cyst in a 10-year-old girl with cough, (a) Chest radiograph shows a round area of increased opacity that deforms the azygoesophageal recess (arrow), (b) CT+C shows a thin-walled water-attenuation cyst adjacent to the esophagus (arrow)

Esophageal duplication cyst

Esophageal duplication cyst

Neurenteric cyst in a 30 year old female with flank pain , (a) Chest radiograph shows a well defined round mass (arrow) in the lower thoracic region , (b- c) Both axial T1 and coronal T2 show a large mass that is of homogenous high signal intensity in the right paravertebral region (arrow) , the cyst presumably contains proteinaceous fluid

7-Pancreatic Pseudocyst :a) Incidenceb) Radiographic Features

a) Incidence :-This follows extension of a pancreatic

pseudocyst in the posterior mediastinum-This occurs via the esophageal or aortic

hiatus and therefore lies adjacent to the esophagus

-Most case are seen in adults with clinical features of a chronic pancreatitis (it can also occur in children following trauma)

b) Radiographic Features :1-Plain Radiography2-CT

1-Plain Radiography :-A space occupying mass in the posterior or

middle mediastinum

Initial examination showed an intrathoracic mass overlying the left margin of the heart (arrowheads) , no interstitial pulmonary edema was noted ,small pleural effusions are shown

2-CT :-A thin walled cyst continuous with the

pancreas -Left sided or bilateral effusions

Pancreatic pseudocyst in a 40 year old male with a 3 week history of chest and epigastric pain , CT+C shows bilateral pleural effusion and periaortic fluid collection (arrow) displacing the esophagus (arrow)

Pancreatic pseudocyst in a 45-year-old woman with a 2-week history of dysphagia and chest pain, (a) CT+C shows bilateral pleural effusion and a thin-walled periaortic cystic lesion that displaces the esophagus (arrow) anteriorly, (b) Axial T1 shows a low-signal-intensity cyst (arrow)

CT+C , a large cystic lesion is compressing the heart , predominantly the left ventricle (arrowheads)

8-Bochdalek Hernia :-See Congenital Pulmonary Lesions

9-Hiatus Hernia :-See Esophagus

Bochdalek Hernia: Axial CT of the lung bases shows abnormal herniation of abdominal fat contents into the lower posterior left hemithorax through the left hemidiaphragm (arrows)

On a frontal chest radiograph (a), the distal third of the azygoesophageal recess demonstrates an abnormal contour and bilateral convexity, lateral chest X-ray (b) demonstrates a retrocardiac hyperlucency mass consistent with hiatal hernia

10-Lateral Meningocele : a) Incidenceb) Radiographic Features

a) Incidence :-A rare lesion due to protrusion of the spinal

meninges through an intervertebral foramen

-Usually asymptomatic-It is commonly associated with

neurofibromatosis (as neurofibroma)

b) Radiographic Features :1-Plain Radiography2-CT

1-Plain Radiography :-A posterior mediastinal mass (often with

pressure deformity on the adjacent bone)-It is indistinguishable from neurofibroma

X‑Ray of the chest showing meningocele as a mass lesion

2-CT :-A fluid filled mass (rather than solid) -Intrathecal contrast medium shows flow into

the lesion

Lateral thoracic meningocele in a 37-year-old man with neurofibromatosis, CT scan shows a low-attenuation mass protruding from the enlarged left intervertebral foramen

Lateral Meningocele in NF

MR demonstrates signal intensity identical to CSF