This document discusses imaging and characterization of anterior and middle mediastinal masses. It begins by outlining objectives of presenting an updated mediastinal compartment classification based on CT landmarks, showing signs to characterize masses on CT/MR, and describing common masses. It then discusses localization of masses using the center method and structure displacement tool. Key points covered include appearance and examples of fat-containing lesions, cysts/cystic lesions, vascular masses, soft tissue masses in the anterior mediastinum, and lymphomas. Common anterior mediastinal masses like thymoma and teratomas are described in detail.

1. Imaging of anterior
and middle mediastinal
masses
G Ferretti
S Lantuejoul
Radiologie Centrale et Imagerie Médicale
Anatomopathologie
CHU Grenoble

2. Objectives
n To present the last version of mediastinal
compartments
n To show the useful signs to characterize
mediastinal masses on CT or MR
n To describe the more common masses
based on density or signal and location

3. Detection of mediastinal masses: CXR
n displaced
n enlarged
n abnormal contours
• lines
• bands
• interfaces
Based on:
n Mass effect
n Abnormal contours of the mediastinum

4. Mediastinal lines: limites
Les lignes médiastinales ne sont pas
constamment visibles (Proto JTI 1987; 2: 47) :
1. Ligne médiastinale postérieure 15%
2. Ligne médiastinale antérieure 60%
3. Interface aortique descendant 100%
4. Ligne paravertébrale gauche 65%
5. Ligne paravertébrale droite 40%
6. Bande para trachéale droite 97%
7. Bouton azygos 98%
8. Bande para oesophagienne 90%

5. n Several traditional mediastinal division schemes exist
based upon arbitrary landmarks on the lateral chest
radiograph (anatomy, surgical, radiology)
n However, CT has replaced CXR and this group proposed
a new division of the mediastinum based on CT
landmarks
n Localization of a tumor within one of the compartments of
the mediastinum
n Narrows the differential diagnosis
n Gives a probability of malignancy of the tumor
n Assist in planning histological sampling
n Assist in planning surgery
International thymic malignancy interest group

6. Number of Compartments
n This clinical classification defines
1. a prevascular (anterior) compartment
2. a visceral (middle) compartment
3. a paravertebral (posterior) compartment
n with anatomic boundaries defined clearly by
CT

7. ITMIG compartiments of mediastinum
n prevascular (anterior)
n visceral (middle)
n paravertebral (posterior)

8. n Posterior limit of the anterior mediastinum is the
anterior aspect of the pericardium as it wraps
around in a curvilinear fashion (thus any vessels
contained within the pericardium are located in the middle
mediastinum)
n contents of the prevascular compartment : the thymus, fat,
lymph nodes, and the left brachiocephalic vein.

9. n Boundaries of visceral mediastinum
n anteriorly—the anterior aspect of the pericardium
n posteriorly—a vertical line connecting a point on the
thoracic vertebral bodies 1 cm posterior to the anterior
margin of the spine

10. Localization of Mediastinal
Abnormalities: CT MRI
two tools are useful:
1. the “center method.” the center of a mediastinal
lesion localizes the abnormality to a specific
compartment.
2. the “structure displacement tool.” Very large
mediastinal masses can displace organs from
other compartments, usually those that abut the
compartment from which the tumor originated.
Carter BW JTO 2014;9:s97-s101

11. Goals imaging
Ø Identification and localization
Ø Description and characterization
Ø Accurate differential diagnosis - short list
Ø Recommendation of a cost effective
imaging and patient management
Ø guiding biopsies
Ø planning surgery
Ø Follow-up
Thacker PG J Thorax Imaging 2015;30:247-264

12. CT
ü Non contrast
ü Arterial phase
ü Venous phase
ü MIP
MRI
ü T1
ü T2 / T2 fat sat
ü T1 Gd
ü MR angiography
ü Cardiac gating
Quality control
US
Nuclear medicine
PET CT
MIBG
CXR
Juanpere S Insight Imaging 2013;4:29-52

13. CT / MRFat or fatty
lesion
Tissue
density
Water
containing
Lymph nodeVascular
origin
Bowel
structure
1-Localization
Center method
Structure displacement tool
2-Characterization

14. Fat containing lesions
1.6–2.3% of all primary mediastinal tumours
Attenuation – 40 to –130 HU
Hyper signal T1
Glazer AJR 1992

15. anterior mediastinum lipomatosis

16. 60 yo man
CXR before aortic surgery.
Middle mediastinum lipoma

17. Giant thymolipoma

18. 18 yo man
3 months coughing

20. Teratoma benign

21. Heterogeneity of teratomas
Common combinations of internal
components of mature teratomas:
n soft tissue, fluid, fat and calcification 39%
n soft tissue, fluid and fat 24%
n soft tissue and fluid 15%
n non-specific cystic lesions 15%
Mature and immature teratomas have the
same presentation
Takahashi K J Magn Reson Imaging 2010; 32:1325–1339

22. Liposarcoma
n Usually symptomatic
n Can range from
predominantly fatty mass
to solid mass with little or
no macroscopic fat
n Differential: lipoma,
thymolipoma, mediastinal
germ cell tumor.

23. Fat containing masses
Anterior mediastinum
• teratoma
• lipoma
• thymolipoma
• hibernoma
Anterior cardiophrenic angle
• fat
• Morgani’s hernia
• teratoma
• lipoma
• thymolipoma
Posterior mediastinum
• fat hernia
All compartments
• lipomatosis
• liposarcoma

24. Cysts and cystic lesions
Mediastinal primary cysts: 15–20% of
all primary mediastinal masses
Water attenuation (not always)
Low signal T1 hyper signal T2
Cyst: no/tiny wall, no
tissue thickening, no
enhancement of the wall,
various density / signal
Cystic tumor
Kim JCAT 2003

25. Bronchogenic cyst

26. 30 yo woman
Esophageal Duplication

27. Foregut duplication cysts (middle
compartment)
n Embryologic origin: Bronchogenic, esophageal,
neurenteric
n 11% of pediatric / 20% of adult mediastinal masses
n only the presence of a vertebral cleft +
mediastinal cyst is specific: neurenteric cyst
n Round / oval smoothly marginated mass
n Tiny / no wall
n 50%: hyperintense T2WI or near 0 HU
n Hemorrhage or infection: higher density /signal
and increase in size

28. 1995 2001
Pericardial cyst

29. Congenital thymic cyst. KYSTE EPITHELIAL thymique bénin de 55 mm de grand axe, développé
sur un parenchyme thymique siège de multiples micro-kystes développés au dépens des
corpuscules de Hassal plus ou moins calcifiés. Pas d'élément suspect de malignité.

30. homme 68 ans 4214
This is not a cyst: the wall is thick and
enhanced
Thymoma with cystic component

31. Thymoma with cystic portion
65 yo man
CT for asbestosis exposure
Thymoma

32. Thymic cyt
n 1% of all mediastinal masses
n Congenital or acquired (inflammation HIV)
n Rare well defined mass with smooth walls, non
enhancing
n CRX: occult
n CT: not always water density: differential solid
mass
n MR > CT: hypo intense on T1 WI and hyper
intense on T2WI; lack of internal enhancement
Ackman JB AJR 2011;197:w15-w20

33. Lympadenopathy central necrosis tuberculosis

34. Cystic masses
True cysts
• Bronchogenic / esophageal
• Thymic
• Pericardial
• Lymphangioma
• Hydatidosis
Masses with cystic component
• Thymoma
• Teratoma
• Lymphoma
• Neurogenic T
• LAP (BK, metastases)
Pseudo-cysts
• pancreatic
Localized
• Pleurisy
• Pericarditis
other
• Meningocele
• lymphocele

35. Vascular masses

36. Aneurism of the descending aorta

37. Oesophageal varices

38. Soft tissue masses of
anterior mediastinum
Strollo Chest 1997
Thacker PG JTO 2014; 30 :247-267

39. 11 ans 17 ans
36 ans 52 ans
Thymus appearance varies with age

40. Normal Thymus on CT
n Detection: frequency
n < 30 yo: 100%
n 30-50 yo: 70%
n > 50 yo: 20%
n Thickness
n < 18 mm if age < 25 y but < 13 mm if age > 25 y
n Smoothly marginated homogeneous gland,
no compression. Convex external borders if >
25 y
n Densité
n Gradual fatty replacement
Nasseri F Radiographics 2010;30:413-428

41. 26 5 2006
13 2 2006
True thymic hyperplasia after stopping chemotherapy.
Diffuse symmetric enlargement of the gland, smooth contour and normal
vessels

42. 32 yo woman myasthenia gravis since 4 years
14 mm thick thymus with contrast enhancemement: Thymoma?
Hyperplasia?
Thymectomy : 28gr thymus with Follicular lymphoid hyperplasia

43. Woman 53 yo (5100)
Thymoma

44. 43 yo man myasthenia gravis (4426)
CT: lesion anterior mediastinum 6 x 3.8 cm
No fat plane between tumor and aorta
Central calcification
thymectomy was possible thymoma B3

45. B3 thymoma with pleural metastases

46. Pericardial extent of a thymoma

47. Thymoma
n Rare in children (1-2% prevascular Tumors)
n Frequent in adults > 40yo
n Thymic epithelial tumor with lymphocytes
n 40% of patients have paraneoplastic syndrome:
myasthenia
n At histology : invasive / non invasive based of the
integrity of the capsule
n CT/MR are not able to precisely define invasive vs.
noninvasive thymoma +++

49. CT and thymoma
n 2 radiological types : presurgical staging
n T1 : well limited mass surrounded of mediastinal fat,
of limited size and various density: encapsulated
thymoma at imaging that may be encapsulated
thymomas or thymomas with limited extracapsular
extension at pathology. Surgery without biopsy
n T II : not well limited mass, large size, heterogeneous
attenuation, with signs of macroscopic extracapsular
extension (medistinum, pleura, pericardial, distant).
Surgery may not be curative. Surgery? TT biopsy?
Inaoka T Radiology 2007 243:869-876

50. Myasthenia and thymus
n At pathology, the thymus of myastenic patients
shows:
n 65% follicular lymphoid hyperplasia
n 15% thymoma
n 20% normal thymus
n 30-50% of thymomas are linked with myasthenia
n Synchronous ou asynchronous
n 25% of patients (woman) are better after thymectomy
Harvard CWH Drugs 1983;26:174-84
Mizuno T Surg Today 1997;27:275-77

51. MRI
n After CT in some cases
n Not > to CT for local extension or for
prognostic value

52. Thymic carcinoma
5691
Man 69 yo
Paralysie diaphragmatique droite

53. 24 yo man. Mass + AFP : 75000 (Yolk Sac Tumor)

54. Nonteratomatous germ cell T (NTGCT)
n Seminomatous T of anterior M
n Large homogenous, lobulated, tumors
n compression of mediastinum
n Nonseminomatous T of anterior M
n Large heterogeneous tumors
n Invasion of adjacent structures, ADP
n Accuracy of CT MRI is not good for histology
n Role +++ of biology
n Elevation of α-fetoprotein (AFP) and/or human chorionic gonadotropin
(HCG) support the diagnosis
Oldenburg J Ann Oncol 2013;24:125-132

56. Ectopic goiter

57. Mediastinal goiter
n direct contiguous growth of a goitre into
the anterior or superior mediastinum.
n encapsulated and lobulated mass with
inhomogeneous appearance (cystic,
calcifications, contrast enhancement)
n Intrathoracic thyroid mass from
heterotopic thyroid tissue without any
connection to the thyroid in the neck is
extremely rare

58. Lymphoma
2-10% of anterior masses in patients >40 yo
n Hodgkin disease (Reed Sternberg cells) ~70%
n mediastinal 60%, young patients,
n NHL T- or B-lymphocytes ~30%
n Large prevascular mass
n Separate/confluent lymphadenopathy or large mass
displacing adjacent structures. No calcification before
treatment
n Role of PET CT > CT / MRI except for DWI MRI
Mayerhoefer ME Clin Cancer Res 2014;20:2984-93

59. 38 yo woman Hodgkin disease

60. 20yo w
NHL

61. Tumor of anterior mediastinum
n Thymus
n Epithelial T
n Thymoma
n Carcinoma
n Germ cell T
n Lymphoma
n Thymic Carcinoid
n Thymolipoma
n Cysts
n other
n Para thyroid
Adenoma
n Lymphangioma
n Endothoracic Goiter
OMS 2004

62. Conclusion
n New anatomic classification
n Role of CT
n Fat within tumor ?
n Cyts vs. cystic tumors
n Surgical vs. non surgical tumors
n Role of biology
n Choice of appropriate biopsy technique