Diagnostic Imaging of Mediastinal Masses

1. RADIOANATOMY OF
MEDIASTINUM &
APPROACH TO
MEDIASTINUM MASSES
DR.AKANKSHA MALVIYA
RMO , RADIODIAGNOSIS

2. ANATOMY
Mediastinum is situated between the lungs in
the centre of the thorax.
Extends :
-From thoracic inlet above
-Central tendon of diaphragm below
-Sternum anteriorly
-Thoracic spine posteriorly
-Parietal pleura laterally

3. DIVISIONSOF
MEDIASTINUM
It is divided by a horizontal plane
extending from sternal angle to lower
border of 4th thoracic vertebra into:
1. Superior mediastinum: above the
plane
2. Inferior mediastinum: below the
plane, it is subdivided into:
Anterior mediastinum: in front of
pericardium
Middle mediastinum: contains heart &
pericardium
Posterior mediastinum: behind
pericardium

4. The Felson method of division is based on findings at
lateral chest radiography

5. CONTENTS OF SUPERIOR MEDIATINUM

6. CONTENTS OF INFERIOR MEDIATINUM

7. 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?

8. INVESTIGATIONS
 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.
Tissue biopsy is required for definitive diagnosis, and surgical resection for definitive
cure.

9. Clues to locate mediastinal mass

11. For example :

12. Lung mass Mediastinal mass

13. HOW TO LOCATE THE MASS IN CHEST PA XRAY
To localize the lesion PA view we have few signs:
1. cervicothoracic sign
2. thoracoabdominal sign
3. hilum overlay sign
4. hilum convergence sign

14. CERVICO-THORACIC SIGN
Anterior mediastinum stops at the level of clavicle.
A – Cervico-thoracic sign (-) B – Cervico-thoracic sign (+)

16. THORACO-ABDOMINAL SIGN
o Posterior costophrenic sulcus extends more caudally
than the anterior basilar lung.
Lesion extending below the dome
– posterior.
Lesion ending at the dome
– anterior.

18. Convergence of the lower lateral margin of the mass towards the spine - mass is
probably entirely intrathoracic
(negative thoracoabdominal sign)

19. Lack of convergence or divergence of lower border – iceberg configuration i.e. a
segment of lesion is hidden below in the abdomen – i.e. the lesion lies partly in thorax
and partly in abdomen.
(positive thoracoabdominal sign)

20. Hilum overlay sign:
• When a mass arises from the hilum, the pulmonary vessels are in contact with the mass
& 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, & is therefore either anterior or posterior to it.

21. Hilum overlay sign:

22. Hilum convergence sign:
• Distinguishes enlarged hilum due to enlarged pulmonary arteries or due to mass
• If vessels directly converge onto hilar shadow - Then the enlargement is vascular.
• If the vessels appear to converge medial to the lateral aspect of the hilar shadow then
the enlargement is due to mass.

23. INTERFACE LINES AND STRIPES
• The air in the lungs abuts various mediastinal structures.
Where the interface is long and vertical it results in a longitudinal or slightly angled line on
the CXR.
• Mediastinal lines:
are thin (<1mm in width) linear opacities that result from contact between two aerated
structures outlining thin intervening tissue on both sides, such as the anterior and posterior
junction lines, azygoesophageal line.
• Mediastinal stripes:
are bands that result from air outlining thicker intervening mediastinal structure, include
the right and left paratracheal stripes.

24. • The thickness of this stripe
should not exceed 4 mm.

25. Thickening right paratracheal stripe is non-specific but may represent:
•lipoma
•paratracheal lymphadenopathy
•thyroid malignancy
•parathyroid malignancy
•tracheal malignancy
•pleural effusion

26. Left Paratracheal Stripe

27. • Left Paratracheal Stripe
Visible on 21%–31% of
PA chest radiographs
• Seen less frequently
than right.

28. Widening of Left Paratracheal Stripe
Large left-sided
pleural effusions
Left paratracheal
lymphadenopathy
Neoplasm
Mediastinal hematoma

29. Right paraspinal stripe:
The right paraspinal line appears straight and typically extends from T8 – T12.
Its presence on 23% of posteroanterior radiographs.

31. Left paraspinal stripe
• Reported on 41% of PA radiographs
• The left paraspinal line is seen more frequently than the right paraspinal line due to the
presence of the descending thoracic aorta on the left

32. Normal left paravertebral stripe. This is the interface
between the lung and the paravertebral soft tissues.
Note that a right paravertebral stripe is not evident.

33. An abnormal contour of the left paraspinal line

34. Anterior junction line:
• Formed where the two lungs abut each
other anteriorly below the level of the
manubrium.
• The line is made up of four layers of pleura
(i.e. the parietal and visceral layers covering
both lungs).
• oblique line crossing sternum
• Obliteration or abnormal convexity of line
suggest anterior mediastinal disease.

36. Posterior junction line:
• Formed where the two lungs
abut each other posteriorly.
• It extends from above the
clavicles to the level of the
arch of the aorta.
• Extends from T3 to T5
vertebrae.
• This line is also made up of
four layers of pleura.

38. Azygo-esophageal recess
The azygo-esophageal recess (also
known as the line/interface) (AER) is a
prevertebral space formed by the
interface of the posteromedial
segments of the right lower lobe and
the azygos veinand esophagus.
The AER extends from the azygos arch
to the aortic hiatus

41. Differentials for masses in various mediastinal
compartments

42. ANTERIOR MEDIASTINAL MASSES :

43. ANTERIOR MEDIASTINAL MASS
The 5 T’s of Anterior Mediastinal Masses
This mnemonic has been used commonly to recall the five most common anterior
mediastinal masses:
5 T’s
1. T – Thymus – Thymoma
2. T – Thyroid
3. T – Terrible lymphoma
4. T – Teratoma and germ cell tumors
5. T – Thoracic Aorta – Dilated or anuerysm of the ascending aorta
Rest other lesions are very rare….
Before you want to biopsy an anterior mediastinal mass, do not forget thta some of
these lesions can be vascular in origin.

44. 1. THYMUS
• The normal morphology and size of the thymus change
markedly with age.
In newborns, the thymus gland is often larger than the heart.
Thymic size decreases with age as the gland undergoes fatty
infiltration. An atrophied thymus is often visualized on CT in
patients in the fourth decade of life, but it is seen in less than
50% of patients older than 40 years.
• The most useful measurement is the thickness of the lobes,
measured perpendicular to the long axis of the gland.
• The normal maximal thickness before age 20 years is 18 mm;
it is 13 mm in older individuals.

45. On x-ray:
THYMIC SAIL SIGN THYMIC WAVE SIGN

46. On CT : Homogeneous, bilobed structure of soft tissue attenuation

47. ON MRI IMAGING:
• Characteristically, the thymus is homogeneous, with intermediate signal intensity (less than that of fat), on
T1-weighted images.
• On T2-weighted images the thymus has high signal intensity, similar to fat, in all age groups; this can make
identification of the thymus difficult in patients with abundant mediastinal fat.

48. THYMICMASSES
Thymic cyst
Thymic hyperplasia
Thymoma
Thymic carcinoma
 Thymic carcinoid
 Thymolipoma

49. Incidental finding on the chest x-ray - a) Thymic cyst
Anterior mediastinal mass with regular and
smooth contours.
Further evaluation with chest CT was
advised.
CT scan confirms that the mass
corresponds to a cystic lesion.

50. b) Thymoma
• account for approximately 20% of all mediastinal tumors and are the most
common primary tumor of the anterior mediastinum.
•most patients are older than 40 years at presentation.
•Although up to 50% of patients with thymoma have myasthenia gravis, only 10%
to 20% of patients with myasthenia gravis have a thymoma.
•Typically unilateral mass anterior to aortic arch

52. c) Thymyolipoma
• Thymolipoma is a rare, benign, well-encapsulated thymic tumour that accounts for
about 2–9% of thymic neoplasms.
• Tumours occur most frequently in the cardiophrenic angle of asymptomatic young
adults without sex predilection.
•The fat content usually constitutes 50–85% of the lesion but has been reported to
account for as much as 95% of the tumour .

53. 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.

54. CT : - Shows a well-defined encapsulated mass that has
extensive fat content and contains small amounts of
solid areas and fibrous septa of inhomogenous soft
tissue density.

55. d) Thymic Hyperplasia
•Thymic hyperplasia is another cause of thymic enlargement.
•In childhood, thymic hyperplasia is most often 'rebound' hyperplasia
associated with chemotherapy, particularly therapy with corticosteroids.
(3 to 10 months after the start of chemotherapy).
•On CT, hyperplasia appears as diffuse enlargement of the thymus, with
preservation of the normal triangular shape.
•The definition of thymic hyperplasia is a > 50 % increase in volume of the
thymus.
•CT, MRI of PET cannot differentiate rebound hyperplasia from infiltration
of the thymus by tumor.

56. •The absence of other active disease and a gradual decrease in thymus size on serial CT's
supports the diagnosis of rebound hyperplasia.
•The thymus usually returns to its normal size in 3 to 6 months.
•On CT, hyperplasia appears as diffuse enlargement of the thymus, with preservation of the
normal triangular shape.

57. e) Neuroendocrine Tumors of the Thymus
• Thymic carcinoid tumor is the most common of this group of tumors

58. • manifest as large, poorly
marginated anterior
mediastinal masses
frequently associated with
intrathoracic
lymphadenopathy.
f) Thymic carcinoma

59. 2. Germ Cell Tumors
• 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.
• Approximately 90 % are benign germ-cell tumors.
• Germ cell tumors usually occur in young adults (mean age, 27 years)
• Most arise in the thymus.
• Three types
• Teratoma • Seminoma • Nonseminomatous Germ Cell Tumor

60. Mediastinal teratoma
Most common mediastinal germ cell tumor

61. Mediastinal Teratoma
• On CT, a benign teratoma is a
well-defined, thick-wall cystic
mass containing a variable mixture
of water, calcium, fat and soft
tissue.
The soft tissue component in
benign teratoma is minimal.
• Size is not an indicator of
malignancy.

62. • Malignant teratomas make up 10 % of all teratomas.
• They tend to have irregular or nodular walls and a predominance of soft
tissue components.
• They also may show pulmonary or liver metastases and chest wall invasion.

63. 3. Thyroid Masses
•Thyroid masses that extend into the mediastinum :
goiter > adenoma , carcinoma , lymphoma.
•Plain Radiography : -Tracheal displacement is the most common finding by CXR
•On noncontrast scans, thyroid tissue is high in attenuation relative to adjacent soft tissues
because of its high iodine content.
•Following the administration of contrast, thyroid tissue significantly enhances.

65. Substernal Thyroid Goiter.
Contrast-enhanced CT of the chest shows a large, contrast-enhancing
mass in the anterior mediastinum containing calcifications and areas of necrosis.

66. Middle mediastinum

67. Mediastinal Lymphadenopathy:
• Mediastinal lymph node abnormalities can be seen in any part of the mediastinum,
although they most commonly involve middle mediastinal regions.
• Thoracic lymph nodes are usually grouped into parietal and visceral.
• Parietal lymph nodes lie outside the parietal pleura, primarily drain structures of the chest
wall ex.
1. internal mammary,
2. diaphragmatic,
3. paracardiac, and
4. intercostal
• Visceral node groups are located within the mediastinum or are related to the lung hila.
• the generally accepted upper limit of normal for short-axis lymph node diameter is 1 cm

68. Causes of mediastinal lymph node enlargement:
• Primary neoplasms of lymph nodes (lymphoma, leukemia)
• Metastases from intrathoracic or extrathoracic primary malignancies.
• Infection (e.g., tuberculosis, fungal infection)
• Nonlymphomatous lymphoid disorders such as Castleman disease

69. 1 – Supra-clavicular, sternal notch nodes
2 – upper paratracheal
4 – lower paratracheal
5 – sub-aortic
6 – para-aortic
inferior mediastinal node
7 – sub-carinal
8 – paraoesophageal
9 – pulmonary ligament
10 – hilar nodes
Lymph node location

75. Lymph Node calcification
Typically, calcified lymph nodes indicate prior granulomatous disease, including tuberculosis,
histoplasmosis and other fungal infections, and sarcoidosis.
Calcification can be dense, involving the node in a homogeneous fashion, stippled, eggshell
in appearance or faint and hazy.
Fig. Selected images
from thoracic CT scan
calcified hilar node
projecting into bronchus
(red arrows).

76. Low-attenuation or
Necrotic Lymph Nodes:
• After administration of
intravenous contrast agent,
enlarged lymph nodes may
appear to be low in attenuation,
often with an enhancing rim
peripherally.
• They are commonly seen in:
1. Active inflammation:
tuberculosis
2. Metastasis

78. Lymphoma
Lymphomas are common mediastinal
neoplasms.
Two main types:
Hodgkins- has a predilection for thoracic
involvement, and up to 85% of patients with
HD present with mediastinal adenopathy.
Multiple node groups are commonly
involved in patients with HD
Non-Hodgkin’s- thoracic involvement is
less common than HD. Involvement of one
node group is much more common in
patients with NHL

80. Mediastinal lymph node enlargement is very
common with sarcoidosis, occurring in 60% to 90%
of patients at some stage in their disease.
The combination of
( 1) right paratracheal,
(2) right hilar, and
(3) left hilar node enlargement
is termed the 1-2-3 pattern/garland triad and
is typical of sarcoidosis..
SARCOIDOSIS:

81. Mediastinal Cysts:
•Most mediastinal cysts are of congenital origin.
• Cysts account for about 10% of primary mediastinal masses.
•Foregut duplication cysts: arise as a result of maldevelopment of the primitive foregut.
1. Bronchogenic cyst,
2. Esophageal duplication cyst
3. Neurenteric cyst.
•Pericardial cysts are mesothelial in origin

82. • Bronchogenic cysts are most
common, representing about 60%
of foregut duplication cysts.
• They probably result from defective
growth of the lung bud during fetal
development.
• Most bronchogenic cysts occur in
the middle mediastinum, typically in
the subcarinal or right paratracheal
region.
• On plain radiographs, bronchogenic
cysts appear as smooth, sharply
marginated, round or elliptical
masses.
Bronchogenic cyst

83. Pericardial Cyst
On plain radiographs, pericardial
cysts are smooth and sharply
marginated . Approximately 90%
of pericardial cysts contact the
diaphragm, with 65% occurring
in the right cardiophrenic angle
On CT, they appear sharply
marginated and their
attenuation is usually similar to
that of water.

84. EsophagealDuplicationCyst
• These cysts are located in the middle or posterior mediastinum and may be
indistinguishable from bronchogenic cysts.
• Usually paraesophageal in location.
Esophageal Duplication Cyst.
White arrows point to a
middle mediastinal soft tissue
mass with sharp margins on
the conventional frontal
radiograph. On the CT scan,
the white arrow points to a
fluid-filled, cystic mass to the
right of the location of the
esophagus. The mass
measured water density.

85. Posterior mediastinum

86. PARASPINAL ABNORMALITIES
•Most frequently, paraspinal masses are neural in origin, including neurogenic
tumors, anterior or lateral thoracic meningocele.
•Infections: paraspinal abscess
•lymph node enlargement
•Rare:extramedullary hematopoiesis

87. Neurogenic tumours
most common tumours to arise in the posterior mediastinum. These lesions can be classified
as:
1. peripheral nerves & nerve sheath tumours
•neurofibromas,
•schwannomas,
•malignant tumors of nerve sheath origin
2. sympathetic ganglia tumors
•ganglioneuromas,
•ganglioneuroblastomas,
•neuroblastomas
3. parasympathetic ganglia tumors
•paraganglioma,
•pheochromocytoma

88. •Peripheral nerve tumors are more common in adults, and sympathetic ganglia tumors are
more common in children.
•CT is usually performed in the initial evaluation of a suspected neurogenic tumor and is
helpful in identifying intratumoral calcification and assessing associated bone erosion or
destruction.
•MRI is the preferred imaging modality for evaluating neurogenic tumors because it allows
the simultaneous assessment of intraspinal extension, spinal cord abnormalities,
longitudinal extent of tumor, and extradural extension.

89. 1. Peripheral Nerve Tumors:
• slow-growing neoplasms & includes schwannomas & neurofibromas
Schwannomas:
• are encapsulated neoplasms that arise from the nerve sheath and typically have areas of
cystic degeneration, hemorrhage, and small focal areas of calcification.
• Schwannomas grow lateral to the parent nerve and cause symptoms by compressing the
nerve.
Neurofibromas:
• differ from schwannomas in that they are unencapsulated and result from proliferation of
all nerve elements, including Schwann cells, nerve fibers, and fibroblasts.
• They grow by diffusely expanding the parent nerve. This type of neural tumor is found in
neurofibromatosis 1 (von Recklinghausen's disease)

90. • On CT both schwannomas and neurofibromas appear as sharply marginated, unilateral,
spherical or lobular posterior mediastinal masses.
Pressure erosion of adjacent ribs or vertebral bodies or enlargement of the neural foramen
occurs in up to 50% of cases. Punctate intralesional calcification occurs occasionally.
• On CT, schwannomas are often of lower attenuation than skeletal muscle due to their high
lipid content, interstitial fluid, and areas of cystic degeneration.
• While the Neurofibromas are often more homogeneous and of higher attenuation than
schwannomas because they have fewer of these histologic features.
• MRI - Variable T1-weighted signal
- high signal intensity peripherally and low signal intensity centrally (target sign) on T2-W.
- 10% may extend appear as dumb-bell-shaped masses with widening of the affected
neural foramen.

91. Schwannoma. A: PA chest radiograph shows
a well-defined, rounded retrocardiac
mediastinal mass.
B: CT shows a left paravertebral mass with
heterogeneous peripheral enhancement
The mass entends into the left neural
foramen (arrows), which is enlarged in
comparison to
the right.
C: Tl-weighted MRI shows extension into the
neural foramen (arrow) to better advantage.
D: T2-weighted MRI also shows extension
into the neural foramen (arrow). The mass
has heterogenous signal intensity.

93. Dumbbell sign of schwannomas

94. T2 MR image shows homogenous high signal
intensity
Shows contrast enhancement
NEUROFIBROMAS

95. A plexiform neurofibroma represents diffuse involvement of a long nerve segment and
its branches, with a “bag of worms” appearance.

96. 2. Sympathetic Ganglia Tumors:
Neuroblastomas
• The posterior mediastinum is also the most common extra-abdominal location of
neuroblastomas.
• Neuroblastomas are highly malignant tumors that typically occur in children younger
than 5 years.
• A posterior mediastinal mass in this age group should be considered a neuroblastoma
until proved otherwise.
• On CT neuroblastomas manifest as paraspinal masses of heterogeneous, predominantly
soft tissue attenuation. The lesions usually contain areas of hemorrhage, necrosis, cystic
generation, and calcium (30%).
• On MRI the lesions typically demonstrate heterogeneous signal intensity on all pulse
sequences and show heterogeneous enhancement.

97. Neuroblastoma presenting as a mass in the posterior
mediastinum
Neuroblastoma grows over several interspaces and frequently
invades the vertebral canal.
The CT-images show a calcified mass in the posterior
mediastinum extending over several vertebrae, which grows
into the vertebral canal

98. On the MR-images the invasion of the vetebral canal is better
seen (arrows).

99. • Mediastinal paraganglioma occur in one
of two locations:
1. aorticopulmonary paraganglioma
2. paravertebral paraganglioma
On CT
- Heterogeneous
- enhance intensely
- hypervascular nature.
3.Parasympathetic Ganglia Tumors:

100. • A characteristic MRI finding of paraganglioma is the presence of multiple
curvilinear and punctate signal voids, which reflect high velocity flow in the
intratumoral vessels

101. • X-ray: sharply marginated, well-circumscribed
paravertebral soft-tissue mass associated with
scoliosis at the same level .usually occur on the
convex side of a scoliosis.
Lateral Thoracic Meningocele
• Are pulsion diverticula & represents
anomalous herniation of the spinal meninges
through an intervertebral foramen or a
defect in the vertebral body.
• most commonly in patients with
neurofibromatosis type 1.

102. • On MRI: diagnosis is established by demonstrating communication with the subarachnoid space. can also be helpful
in differentiating meningoceles from neurofibromas.
T1W- hypointense T2W-hyperintense
on contrast: no enhancement while the neurofibromas shows enhancement on contrast scan.

103. • Vertebral osteomyelitis can result in a paraspinal abscess.
Paraspinal Inflammation
• On CT, a paraspinal abscess
appears as a mass of
heterogeneous attenuation.
• Rim enhancement following
the administration of
intravenous contrast is
characteristic.
• narrowing of the adjacent
intervertebral disc and
destruction of two or more
contiguous vertebral bodies.

104. EXTRAMEDULLARY HEMATOPOIESIS
• Extramedullary hematopoiesis is usually seen in patients with
chronic hemolytic disorders such as thalassemia, hereditary
spherocytosis, sickle cell disease.
• The masses are usually bilateral, contain no calcification, and
cause no rib destruction.
• On CT: heterogeneous mass or masses, often with focal areas
of fat within the lesion.
• On MRI: T1- and T2-weighted MR images typically show
bilateral heterogeneous masses with increased signal intensity
on T1-weighted images because of fat within the masses.

105. THORACIC AORTIC ANEURYSM
• Aortic diameter exceeding 4 cm is called dilatation, and a diameter over 5 cm is termed an aneurysm. most
commonly involve ascending aorta.
• Atherosclerosis is the most common cause of aneurysm.
Fusiform
dilatation of
descending
aorta with
calcification in
its wall.

107. THANK YOU 