This document discusses the classification and diagnostic approach to fine needle aspiration cytology (FNAC) of mediastinal tumors. It describes the various tumor types that can occur in the mediastinum, including thymic tumors, germ cell tumors, lymphomas, and others. For each tumor type, it provides details on cytological features, differential diagnoses, immunohistochemistry findings, and other diagnostic information useful for FNAC-based diagnosis of mediastinal masses. The goal is to simplify the classification and provide guidance on distinguishing between benign and malignant mediastinal tumors using cytology samples.

1. DR. INDIRA SHASTRY.K
KASTURBA MEDICAL COLLEGE
MANIPAL UNIVERSITY, MANIPAL.
Classification and diagnostic
approach to FNAC of
mediastinal tumours

2. Mediastinum

4. • CT : locating small lesion in thoracic inlet, hilum and
middle mediastinum , via supraclavicular, suprasternal
and parasternal approach. But continues real time
monitoring is not possible without radiation exposure.
• USG :
• via percutaneous route ; it provides both spatial
orientation as well as real time monitoring with out
exposure to radiation
• Via bronchoscopy / endoscopy via oesophagus.
Approach to mediastinum

5. • Epithelial tumors
• Thymoma
• Thymic carcinoma
• Germ cell tumors
• Pure GCT’s : GCT’s with only one histological type
• Mixed GCT : GCT with more than one histological type
• GCT’s with somatic type malignancy
• GCT’s with associated malignancy
WHO Classification of thymic tumors
and mediastinal tumors

6. • Mediastinal lymphomas and haematopoietic neoplasms:
• B-cell lymphoma
• T-cell lymphoma
• Hodgkin’s lymphoma
• Histiocytic and dendritic cell tumors
• Myeloid sarcoma and extra-medullary acute myeloid leukaemia
• Mesenchymal tumors of mediastinum:
• Thymolipoma
• Lipoma of mediastinum
• Liposarcoma of mediastimum
• Solitary fibrous tumors
• Synovial sarcomas

7. • Vascular neoplasms
• Rhabdomyosrcoma
• Leiomyomatous tumors
• Peripheral nerve sheeth tumors
• Ectopic tumors of mediastinum
• Ectopic tumors of thymus
• Ectopic tumors of thyroid
• Ectopic tumors of parathyroid
• Metastasis to thymus and to anterior mediastinum

8. To simplify
Benign Maliganat
Thymoma
Benign teratoma
Neurilemmnoma
Neurofibroma
Paraganglioma
Thymic carcinoama
Lymphoma
Seminoma
Embryona carcinoma
Yolk sac tumor
Choriocarcinoma
Immature teratoma
Neuroblastoma
Metastatic tumors

9. • Located in superior and / or anterior mediastinum.
• Can occur in all age groups but MC seen in in adults and peaks
in 6 th decade.
• 10-80 % have symptoms of MG
• Histological classification of thymoma is confusing. According to
updated WHO, thymoma has been classified in to 3 catagories –
• Thymoma with spindle bland looking neoplastic cells ( type A )
• Thymoma with round to polygonal neoplastic cells ( type B )
• Mixed thymoma ( type AB )
Thymoma

10. • Thymoma :
• Type A ( spindle cell; medullary)
• Type AB ( mixed )
• Type B1 ( lymphocyte rich; lymphocyte predominantly cortical;
organoid )
• Type B2 ( cortical )
• Type B3 ( epithelial ; atypical; squamoid ; well differentiated
squamous cell carcinoma)
• Micronodualr thymoma
• Metaplastic thymoma
• microscopic thymoma
• Scerosing lipoma
• lipofibroadenoma
WHO classification

11. • Dual population of epithelial cells and lymphocytes in
varying proportions.
• Cytological appearance depends on relative population of
• Epithelial V/S lymphoid cells
• Medullary V/S cortical component
Key diagnostic features of thymoma on FNAC

12. • Cohesive sheets – cytologically bland and mitotically inactive
spindle cells , with sprinkling of small lymphoid cells ; pseudo
glandular spaces some times seen.
• Elongated ovoid nuclei, delicate nuclear membrane, fine
chromatin , inconspicuous nucleoli and ill defined cell borders.
• Cyto-architecture : arranged in short fascicles and whorls with
focal storiform architecture.
Thymoma with predominance of medullary
component : type A/ spindle cell/ medullary
thymoma

13. • Small no of extremely
elongated “ fibroblast like “
spindle cells may be seen.
• Hassall corpuscles are absent.
• IHC:
• Ck (+) , CD 20 (+) – epithelial
cells .
• Background lymphoid cells
TDT negative.
• Thymic medullary cells CD
57 (+) neoplastic cells CD5(-)
CK 3
CD 20

14. • Type B3 thymoma ( well differentiated thymic carcinoma ) :
CD 20 – ve, koilocyte like cortical epithelial cells.
• Metastatic spindle cell carcinoma : loosely dispersed single /
dys-cohesive clusters of more pleomorphic tumor cells. ,
• Spindle cell malignant melanoma : prominet nucleoli ; more
cellular dispersion ; melanin pigment +/-
• Basaloid ( CD 20 – ve / CD 5 + ve)/ sarcomatoid type spindle
cell carcinoma
• Soft tissue tumors ( solitary fibrous tumors and synovial
sarcoma ) – IHC
• Spindle cell carcinoid
• Benign mesothelial cell clusters
Differential diagnosis

15. • Small lymphoid cells mimicking lymphoid lesion.
• Small no of loosely cohesive and bland looking large
polygonal cells containing round to ovoid nuclei, fine
chromatin, inconspicuous small nucleoli, ill-defined cell
borders among sea of small lymphoid cells
• Solitary small nucleoli may be seen specially in B2 type;
• In general these cells are 4 times the size of a small
lymphocyte.
Thymoma with predominance of cortical
component

16. • Some times abortive hassall
corpuscles seen – B2 type
• Plasma cells not seen,
lympho-glandular bodies not
apparent – R/O lymph node
( reactive )
• IHC : epithelial cells – Ck
positive , CD 57 focally
positive, background
lymphoid cells are TdT, CD1a
and CD99 positive

17. Differential diagnosis :
• Reactive lymphoid hyperplasia : polymorphous population of
lymphoid cells along with tingible body macrophages, and
lympho-glandular bodies.
• Cytological distinction between thymus and thymoma are
difficult.
• Follicular lymphoma : CK and TdT negative
• Precursor T lymphoblastic lymphoma: CK negative.
• Lympho-epithelioma like thymic carcinoma : EBV
associated, more nuclear pleomorphism, no dendritic
cytokeratin staining pattern.

18. • Well differentiated thymic carcinoma –muller-
hermelink classification ( WHO-B3) is different entity ,
than thymic carcinoma.
• Thymic carcinoma is rare- mainly adults.
• Cytomorohological features of thymic carcinoma
are highly variable and virtually indistinguishable
from non- small cell carcinoma of non thymic origin.
Thymic carcinoma

19. • Abundant malignant cells
with varying degree of
cohesiveness. Coagulative
tumor necrosis +/-
• Nuclear pleomorphism ,
prominent nucleoli, coarse
chromatin,
• IHC : CK , CD-5, CD-117,
positive and CD-57
negative.

20. • Squamous cell carcinoma – 90% in asia.
• Basaloid carcinoma
• Mucoepidermoid carcinoma
• Lymphoepithelioma like carcinoma
• Sarcomatoid carcinoma
• Clear cell carcinoma
• Adenocarcinoma
• Papillary adenocarcinoma
• Well – differentiated neuroendocrine neoplasm ( typical and
atypical )
• Poorly differentiated neuroendocrine carcinomas ( large cell
and small cell )
• Undifferentiated carcinoma
• Combined thymic epithelial tumors ; including neuroendocrine
tumors
WHO classification

21. • Metastatic carcinoma : CD-5 neg
• Thymoma with predominant medullary component : bland
looking, mitotically inactive spindle cells.
• Thymoma with predominant cortical component : bland
looking polygonal cells with TdT positivity.
• Seminoma .
• Primary mediastinal large B cell lymphoma.
Differential diagnosis :

22. • Often occur in anterior mediastinum : 2-4 % of thymic
carcinoma.
• May be associated with Cushing's syndrome, 25 % associated
with MEN I.
• Further divided in to:
• Well differentiated neuroendocrine carcinoma( typical and
atypical )
• Poorly differentiated neuroendocrine carcinoma ( large cell and
small cell type )
Thymic neuroendocrine tumors

23. • Monotonous population.
• Dispersed and in loosely
cohesive pattern.
• “Plasmacytoid “ tumor cells,
ecentrically placed nuclei.
• Finely stippled chromatin
and granular eosinophilic
cytoplasm
• Pseudo inclusions +
• “ comet like phenomenon “
– tumor cell nucleoli
dragging cytoplasm behind.

24. • Seminoma
• Embryonal carcinoma
• Yolk sac tumors
• Choriocarcinoma
• Teratoma ; mature
• Teratoma; immature
Germ cell tumors

25. • K/as primary mediastinal seminoma / germinoma.
• 8% of all extra gondal germ cell tumors and 2nd MC
mediastinal germ cell tumor.
• Males ; > 50% occur in 30-40 yr age.
• Distinction between primary and secondary tumors are
based entirly on clinical background rather cytological
bacground.
Seminoma

26. • Smears : abundunt cellularity.
• Dispersed or in loosly
cohesive clusters.
• Necrotic cellular debris,
lymphoid cells, and histioid
cells in “ tigroid “
background.
• Large round ovoid nuclei,
vesicular chromatin,
prominent solitary
eosinophilic nucleoli and
fragile cytoplasm.
• Mitosis and apoptosis is
common.
• IHC: CD-117, PLAP pos. CK –
focally / weakly pos.

27. • Thymic carcinoma : CK , CD-117 and CD-5 pos
• metastatic non-small cell carcinoma – CK pos and
CD-117 neg
• Primary mediastinal large B cell lymphoma: B cell
markers pos and CD-117 neg
• Anaplastic large cell lymphoma : CD-30 pos and T
cell markers pos
• Metastatic malignant melanoma ; S-100, HMB 45
pos .
Differential Diagnosis

28. • MC mediastinal germ cell tumor ( 50-70 % )
• Mature teratoma : adult type tissue
• Immature teratoma: immature embryonal type of tissue;
exclusively affects males,
• Mostly benign;
• Mixture of somatic tissue ; ectoderm, endoderm,
mesoderm.
• Immature teratoma : biphasic cell pattern ; loose
aggregates of small round cells in fibrillary matrix
represents neuronal component.
• Malignant transformation can occur : MC is SCC or
adenocarcinoma.
Teratoma

29. • Admixture of epithelial and
mesenchymal elements
• Bland looking epithelial (
squamus / coulmnar ) cells
with neural component :
small round cells.
• DD: from bronchogenic cyst
: cystic change in mature
teratoma can immitate.
• Granulomatous response
can be mistaken for
tuberrculosis.
• Squamous flakes and
epithelium can be mistaken
for SCC.
• R/O mixed germ cell tumor
with teratomatous
component

30. • Rare type of non seminomatous germ cell tumor in young
males.
• Often associated with teratoma ( teratocarcinoma ),
Choriocarcinoma, or seminoma.
• Cytologically embryonal carcinoma is indistinguishable
from poorly differentiated carcinoma of non germ cell
origin.
• Mitotically active tumor with malignant cells arranged in
poorly cohesive 3 D clusters , with syncitial growth pattern.
Embryonal carcinoma

31. • Nuclear overlapping, vesicular
chromatin with prominent
nucleoli, with small to
moderate amount of
cytoplasm and ill defined cell
borders.
• IHC : CK, CD- 30 pos,
EMA, vimentin, CD-117 and
CD_5 neg.
• Differential diagnosis:
• Thymic carcinoma.
• Metastatic non-small cell
carcinoma.
• Yolk sac tumor.

32. • Rare mediastinal tumor can occur both in paediatric ( female
predilection ) as well as in adults ( male predilection ).
• Commonly associated with elevated AFP levels.
• Coagulative tumor necrosis is abundant
• Schiller- Duval bodies/ Glomeruloid bodies – diagnostic are
seldom seen.
• Identification of eosinophilic “ basal –lamina like “ substances
and intra-cytoplasmic hyaline globules ( PAS + & diastase
resistant), give clue to diagnosis.
Yolk sac tumor / endodermal sinus tumor

33. • Small clusters and sheets of
pleomorphic tumor cells
• +/- microglandular and
papillary pattern.
• Round to ovid nuclei, small
nucleoli, scanty some times
vacuolated cytoplasm, varying
degree of pleomorphism.
• IHC : CK +, AFP variably +, CD-
30, CD-117, & CD-5 neg.
• DD:
• Embryonal carcinoma.
• Thymic carcinoma
• Metastatic non-small cell
carcinoma.

34. • Pure medastinal choriocarcinoma is extremely rare – virtualy
non existent in children.
• Highly aggresive tumor.
• Elevated S.β HCG level.
• Mixture of syncytiotrophoblasts and cystotrophoblasts against
haemorrhagic background.
• Syncytiotrophoblastic giant cells with eosinophilic cytoplasm ,
pleomorphic nuclei, prominent nucleoli,
• Cytotrophoblasts are medium sized cells with vaculated
basophilic cytoplasm.
Choriocarcinoma

35. • Primary mediastinal large B cell lymphoma
• Precursor T lymphoblastic lymphoma/leukemia
• Anaplastic large T cell lymphoma , mature T cell
lymphoma.
• MAT lyphoma.
• Hodgkin’s lymphoma.
• Histiocytic and dendritic cell tumors
• Myeloid sarcoma and extra-medullary acute
myeloid leukaemia
Lymphomas

36. • Affects young adults of 30-40 yrs
• Slight female predilection, MC present with superior venacaval
syndrome. Generalised lymphadenopathy and HSP is rare.
• Monotonous population of dispersed large lymphoid cells
• Mitotocally active large “ centroblast “ like cells ;
• lymphoglandular bodies +
• IHC : B cell markers + , CD-23 + , CD-10 and CD- 15 negative
Primary mediastinal large B cell lymphoma

37. Monomorphic population ; centroblast like cells with round nuceli and
several small basophilic nucleoli.

38. • DD:
• seminoma ( CD-117 + , CD-20 - ) ,
• poorly differentiated small cell carcinoma ( CK +,
CD 5 + if thymic origin, CD 20 neg ),
• Hodgkin’s lymphoma ( CD-30 and CD-15 pos )
• Anaplastic large cell lymphoma ( CD-30 , T cell
markers pos , EMA sometimes +, CD-20 neg )
• Metastatic malignant melanoma ( S100 and HNB
45 pos )

39. • Children and in young adults.
• Heterogenous population of atypical lymphoid cells and
polymorphs.
• Atypical lymphoid cells of various morphology : “ hallmark
cells” , “ plasmacytoid cells “, “ hand mirror cells “,
multinucleated cells with “ wreath like” arrangement of
nucleus, multilobulated nucleus cells, and non descript
small round cells.
• DD: poorly differentiated non small cell carcinoma, primary
mediastinal large B cell lymphoma, hodgkin’s lymphoma,
metastatic malignant melanoma.
Anaplastic large cell lymphoma

40. Hallmark cell with embryo like nucleus Doughnut cell
Hand mirror Multinucleated Multilobated

41. • Childhood and in adolescence .
• Male predominance
• Typically involves thymus and mediastinal lymphnode;
associated pleural and pericardial effusion, superior
mediastinal syndrome and tracheal compression.
• Cytology : “ sea of small lymphoid cells “
• Monotonus population of mitotically active small lymphoid cells
• “ No atypical lymphoid cells “
• lymphoglandular bodies +
Precursor T lymphoblastic lymphoma

42. • DD:
• Cortical type of thymoma : B1 and B2 :a diagnostic
pitfall, demonstration of monoclonality proves
malignancy .
• Reactive lymphoid hyperplasia : TDT neg
• Low grade non-Hodgkin’s lymphoma
• Neuroblastoma
• Rhabdomyosarcoma
• Small cell carcinoma
TdT

43. • From post-germinal centre activated B cells.
• Female predilection ; late adults / in 30‘s
• MC : nodular sclerosis type
• Cytology : heterogenous population of lymphoid
cells with “ Reed- Sternberg” like cells associated
with lymphocytes plasma cells, eosinophils and
histeocytes in background.
• IHC : CD-30 and CD-15 positive
• DD : primary large B cell lymphoma , anaplastic
large cell lymphoma
Hodgkin’s lymphoma

44. • Commonest neurogenic tumor in mediastinum.
• Common in posterior mediastinum : develop from peripheral
nerve, sympathetic and parasympathetic ganglion , neural tube
embryonic remnants.
• Neurofibroma : small loosely cohesive groups of spindle cells in
disorderly arrangement , non specific.
• Focal pleomorphism of nucleus can be seen.
• Features of Neurilemmnoma are rather specific :
• Spindle cells associated with fibrillary matrix
• Mitotically inactive oval nuclei, sometimes “ fish –hook “ nuclei, with
fine chromatin; occ pseudo-nuclear inclusions.
• Rarely Verocay body formation seen
Neurilemmnoma ( schwannoma ) &
neurofibroma

46. • Tumor of infancy 1-10 yrs
• Occur in posterior mediastinum
• Cytology : loose aggregates of small round cells with various
amount of fibrillary matrix, in loosly cohesive clusters or in
isolation.
• Bland looking with indiscriminant small nucleoli, some nuclear
moulding +
• Vague rosette formation may be seen ( HW )
Neuroblastoma

48. • Ganglioneuroma
• Granular cell tumor
• MPNST
• Ganglioneuroblastoma
• Paraganglioma
• Pigmented neuroectodermal tumor of infancy
Other Neuronal tumors

49. • Majority of mediastinal neoplasms.
• MC from lung and are small cell type followed by breast, thyroid
and prostate.
Metastatic tumors
SCC AdenocarcinomaSmall cell carcinoma

50. • Morphologic heterogeneity with in lesion.
• Stromal sclerosis resulting in low cellularity.
• Poor preservation due to extensive necrosis ; seminoma.
• Sampling error due to cystic change: thymoma, thymic
carcinoma, seminoma, mature teratoma – yield cyst fluid
only.
• Abundant lymphocytes obscuring diagnostic cells : cortical
thymoma – reactive LN and other lymphoma, IHC is
necessary for demonstrating clonal population.
• Thymic carcinoma ( < 30yr ) is indistinguishable from
metastatic carcinoma ( older ) on cyto-morphology.
Diagnostic pitfalls

51. • Mediatinal germ cell tumors; non seminomatous can be
mistaken for poorly differentiated non small cell carcinoma
of lung – clinical and serological correlation required for
diagnosis.
• Stromal sclerosis is seen in some of lymphoid malignancy :
primary mediastinal large B cell lymphoma and nodular
sclerosis type of HL .
• If mediastinal FNAC contain monotonus population of small
round cells the list of DD: T- lymphoblastic lymphoma, low
grade NHL, neuroblastoma, Ewing’s sarcoma/primitive
neuroectodermal tumors, rhbdomyosarcoma, small cell
carcinoma.

52. Diagnosis requires combination of clinical, radiological,
biochemical, and cytomorphological information.
• Age :
In children : commonest thymic tumor is NHL. Thymoma is
extremely rare in childhood.
Adults : mets and benign mediastinal cyst of celomic origin or
GI origin.
In adults : thymoma represents commonest primary thymic
tumor, followed by mediastinal lymphoma.
Approach to mediadiastinal tumors
Step 1 : clinical history

53. • located in which part of mediastinum
• Extremely useful in diagnosis of tumors
• Depending on predominant cell morphology diagnosis
can be approached.
Step 2 : radiological localisation
Step 3 : cytomorphology

54. History and relevant information for diagnosis

56. Small cell
rich lesion
Monotonous
small lymphoid
cells
Precursor T
lymphoblastic
lymphoma , extra
nodal marginal B
zone lymph
Polymorphous
lymphoid cells
Reactive
lymphnode /
Hodgkin’s
Admixed non
lymphoid large
tumor cells
Thymoma with
predominance of
cortical
component
Non lymphoid
small tumor cells
Neuroblastoma,
Ewing’s, PNET,
rhabdo, small cell
Ca

57. Large cell
rich lesions
Cohesive large
tumor cells
Thymic carcinoma,
non seminomatous
germ cell tumors
Loosely
cohesive large
cells
Thymic
neurendocrine
tumor, seminoma,
some metastatic
carcinoma
Widely
dispersed large
tumor cells
Diffuse large B cell
lymphoma,
anaplastic large
cell lymphoma

59. Spindle
cell rich
lesions
Reactive
fibroblast &/
histiocytes
Granulomatous
lymphadenitis , chronic
sclerosing mediastinitis,
nodular sclerosis HL, deep
fibromatosis
Bland looking
spindle cells
Thymoma ( medullary),
spindle cell thymic
carcinoid, neurofibroma,
neurilemmnoma.
Malignant
spindle cells
Metastatic MM, diffuse
large B cell lymphoma
with sclerosis, sarcomas,
spindle cell SCC.

62. Ancillary techniques for mediastinal tumors

63. • Establish primary pathologic diagnosis, or separating
surgical from non-surgical cases.
• Staging of primary lung cancer.
• Detecting residual disease or recurrent tumor after therapy.
• Rapid diagnosis of mediastinal neoplasm.
• When definitive diagnosis not possible : guide clinician in
planning subsequent management approach.
conclusion

64. • WHO pathology and genetics – tumors of lung, pleura, thymus and
heart. 2004.
• Comprehensive cytopathology . M.Bibbo, 3rd ed.
• Surgical pathology. Rosai and Ackerman’s. 10th ed.
• Pranab dey. Diagnostic dilema: diagnostic algorthem in fine needle
aspiration cytology of mediastinal tumors. Indian journal of
pathology and microbiology. 2010. 53. 395-402.
References :