1. Discussion Diagnostic approach of mediastinal masses on image
Thymoma v.s. Bronchogenic cyst
Other methods of diagnostic radiology
Thoracic Radiology THE REQUISITES Ch 15~16
Eur. Radiol. 8, (1998)

2. Diagnostic approach of mediastinal masses on image

3. The 4 D’s of mediastinal masses
Detection: mediastinal landmarks
Lines
Stripes
Interfaces
Descriptive features of mediastinal masses
Intimate effect on mediastinal structures
Smooth, sharp margins
Obtuse angles with adjacent lung
Division of the mediastinum
Differential diagnosis

4. Detection: mediastinal landmarks
Lines
Anterior junction line
Posterior junction line
Right and left paraspinal lines
Stripes
Right paratracheal stripe
Interfaces
Azygoesophageal interface
Descending aortic interface

5. Anterior and posterior junction lines
Detection of a displaced junction line allows both identification of a mediastinal abnormality and localization as either anterior or posterior

6. Anterior and posterior junction lines

7. Right and left paraspinal lines
Displacement of the left paraspinal line lateral to the descending aortic interface signals the presence of a posterior mediastinal abnormality
An ectatic aorta may displace the left paraspinal line laterally
Lymphoma

8. Right paratracheal stripe
Lymphadenopathy
It is seen as a smooth stripe of uniform width (<3mm)
Widening of the right paratracheal stripe is a sign of middle mediastinal pathology

9. Right paratracheal stripe

10. Azygoesophageal interface
Bronchogenic cyst
A focal convexity of the azygoesophageal interface signals the presence of a mediastinal abnormality

11. Descending aortic interface
Abnormalities in the descending aortic interface imply pathology within the posterior mediastinum
Descending thoracic aortic aneuryam

12. Descriptive features of mediastinal masses
Lung mass
Intimate effect on mediastinal structures
Dose not usually produce an intimate effect
Smooth sharp margins
Usually irregular margins
Obtuse angles
Acute angles

13. Descriptive features of mediastinal masses
Thyroid adenoma

14. Division of the mediastinum
Anterior mediastinum
Boundaries
Anteriorly by the sternum
Posteriorly by the anterior margins of the pericardium, aorta, and brachiocephalic vessels
Normal structures
Thymus gland, lymph nodes, fat, internal mammary vessels

15. Division of the mediastinum
Middle mediastinum
Boundaries
Posterior margin of anterior division and anterior margin of posterior
Normal structures
Heart and pericardium, ascending and transverse aorta, brachiocephalic vessels, SVC and IVC, main pulmonary vessels, trachea and main bronchi, lymph nodes, fat
Posterior mediastinum
Boundaries
Anteriorly by the posterior margins of the pericardium and great vessels
Posteriorly by the thoracic vertebral bodies
Normal structures
Descending thoracic aorta, esophagus, thoracic duct, azygous/hemiazygous, autonomic nerves, lymph nodes, fat

16. Differential diagnosis
Anterior mediastinum
Thymoma, lymphoma, germ cell neoplasms, thyroid abnormalities
Middle mediastinum
Lymphadenopathy, bronchogenic cyst, vascular abnormalities, pericardial cyst, tracheal tumor
Posterior mediastinum
Neurogenic tumors, paravertebral abnormalities, vascular abnormalities, esophageal abnormalities, lymphadenopathy, neurenteric cyst, Bochdalek hernia, extramedullary hematopoeisis

18. Thymoma v.s. Bronchogenic cyst

19. Thymoma
Thymomas are tumors composed of an admixture of thymic epithelial cells and reactive lymphocytes
Account for the majority of anterior mediastinal masses in adults and typically occur as incidental findings
Associations
Myasthenia gravis, hypogammaglobulinemia, red cell aplasia
Age
Usually 40~60; unusual in patients < 30
Gender
Male and females, equally

20. Non-invasive thymoma Descriptive features
Round or oval well-circumscribed, soft-tissue density mass growing asymmetrically to one side of the anterior mediastinum
Slightly increases with administration of contrast material
Calcifications at the periphery of the lesion or throughout its substance, hemorrhage, or necrosis can also be seen
Areas of cystic degeneration are common
Usually located anterior to the junction of the heart and great vessels
Magnetic resonance imaging has a limited role in the
evaluation of thymomas
vascular
and cardiac extension of invasive thymoma is well identified
by MRI

21. Invasive thymoma Descriptive features
Appears on CT as an irregular ill-defined mass
Additional findings of invasion of adjacent mediastinal structures, chest wall invasion, or contiguous spread along pleural surfaces
Direct contact and absence of cleavage planes are not strictly reliable criteria to predict invasion
Clear delineation of fat planes surrounding a tumor should be interpreted as indicating an absence of extensive local invasion

22. Thymoma

23. Bronchogenic cyst
Bronchogenic cysts are the result of an abnormality in primitive foregut development
Have a fibrous capsule, often contain cartilage, smooth muscle, are lined by respiratory epithelium, and contain mucoid material
Occur in all three mediastinal compartments, but the middle mediastinum is the most common site
Age
Often seen in younger patients, but may be detected at any age

24. Bronchogenic cyst Gender
Male and females equally
Usually occur as an incidental finding, but they occasionally cause symptoms secondary to compression of adjacent structures
Infrequently, they may cause symptoms secondary to infection

25. Bronchogenic cyst Descriptive features
Subcarinal or right paratracheal locations
Well-defined, homogeneous mass with imperceptible wall
Fluid or soft-tissue attenuation on CT
On rare occasions they show an extremely high density related to a milk of calcium content
Curvilinear calcification of the wall is possible
At MRI they frequently show a signal intensity higher than that of muscle on T1-weighted images due to their high proteinaceous content
The signal intensity on T2-weighted images is very high, suggesting a cystic lesion

26. Bronchogenic cyst

27. Other methods of diagnostic radiology

28. Ultrasonography
Transthoracic US is not currently used in mediastinal mass evaluation
The major limitation is an inadequate window
Useful information can be obtained especially in children in masses abutting the chest wall and in vascular abnormalities
May be used to differentiate cystic from solid masses and relate them to surrounding structures
Helpful in the evaluation of masses in close proximity to the heart and pericardium, a setting in which an assessment of extracardiac and intracardiac structures may be helpful

29. Biopsy
A preoperative histological diagnosis is unnecessary if the mass seems reasonably resectable
If the mass is clearly invasive and looks unresectable, then a biopsy, either guided by imaging or surgical, is indicated
Small, encapsulated, "typical" thymomas are excised for diagnosis and treatment. Large, invasive, "atypical" thymomas are best managed by biopsy to learn the histology of the tumor and to assess its invasive potential

30. Thanks for your attention !!