Muller hermelink – well differentiated SCC ; B3 thymoma
IHC : CK 3 and aberrant expression of CD 20
SFT – CD 99, CD 34, bcl-2 positive and CK neg Synovial sarcoma - CK is weakly and focally positive , CD 20 neg and CD 5 pos Malignant melanoma : S100 , HMB-45 pos and CK neg Most of benign mesothelial clusters are calretinin positive ( ovoid nuclei nuclear folding +/-, fine chromatin, delicate nuclear membrane, moderate amount of amorphophilic cytoplasm and window bwn cells.
Small eosinophilic nucleoli are seen especially in B2 type of thymoma. Thymoma with cortical predominant architecture is very difficult to distinguish from reactive lymphnode. In type B1 or B2 thymoma tingible body macrophages are also seen.
Fig A &C are of B2 thymoma Fig F is B1 thymoma – cell block – CK 3 staining dendritic cell type.
No associated MG or hypogammaglobulinemia.
Cohesive sheets of malignant cells with areas of coagulative necrosis, and aberrant expression of CD 5 in cell block preparation.
1 st MC mediastinal germ cell tumor is teratoma.
Tigroid Background is seen in glycogen-containing tumors: Ewing’s sarcoma, Seminoma, SCC , clear cell carcinoma , Primary large B cell lymphoma Fig shows loose aggregates of maononuclear cells with stipled nuclei and necrotic background. Higher power shows round to ovid cells with delicate nuclear membrane, prominent nucleoli, and fragile cytoplsm. CD117 positive and histopathology shows associated granulomatous inflammation
Mature teratoma shows : squamous epithelium, hair shaft, respiratory epithelium, chondromyxoid stroma which is better demonstrated with diff stick ( MGG ) stain- Metachromatic colour.
R/O mixed germ cell tumor with teratomatous component : especially when there is immature component.
Occur either as mixed or pure form. AFP levels are elevated in all cases.
Poorly cohesive clusters of pleomarphic cells, mot like those cells seen in poorly differentiated carcinoma H/P shows marked nuclear pleomorphism of nucleus with nuclear overlapping and crowding , vesicular nucleus, prominent nucleoli, illdefined basophillic cytoplasm.
S-D bodies are formedd due to invagination of tumor cells and capillaries in to cystic space.
Pleomorphic tumor cells associated with Ribbon like basal lamina like substance H/P shows Schiller duvel bodies and AFP positive in cytoplsm
Haematogenous spread , pt present with features of gynacomastia. Practically speaking – the ability of FNAC in separating various non semonomatous germ cell tumors, specially between embryonal carcinoma, yolk sac tumor, and choriocarcinoma are rather limited. There is often morphological overlap and its not uncommon to find mixture of various germ cell tumor components with in single lesion.
Nuclear membrane irregularities noted
Widely dispersed atypical lymphoid cells of various morphology “ hallmark cells “ – ecentric kidney shaped or embyo-like nuclei, with several rod like or angulated basophilic nucleoli and abundunt amorphophillic cytoplsm “ Doughnut “ cells – tumor cells with multilobated nuclei, and multinucleated giant cells with “ wreath –like “ arrangement.
No atypical lymphoid cells “
IHC : TdT pos
both neurilemmnoma and neurofibroma yeilds spindle cells.
MG : myasthenia grevis , HSM : haepato-spleenomegaly. Taking the anatomic location of the lesion and age of the patient in to consideration, a narrow list of DD can be produced even before FNAC. clinical H/o of MG associated with thymoma . past H/o of malignancy . lymphadenopathy, HSM, others .
Classification and diagnostic approach to fnac of mediastinal
DR. INDIRA SHASTRY.K
KASTURBA MEDICAL COLLEGE
MANIPAL UNIVERSITY, MANIPAL.
Classification and diagnostic
approach to FNAC of
• 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
• Epithelial tumors
• 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
• 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:
• Lipoma of mediastinum
• Liposarcoma of mediastimum
• Solitary fibrous tumors
• Synovial sarcomas
• Vascular neoplasms
• 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
• 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 :
• Type A ( spindle cell; medullary)
• Type AB ( mixed )
• Type B1 ( lymphocyte rich; lymphocyte predominantly cortical;
• Type B2 ( cortical )
• Type B3 ( epithelial ; atypical; squamoid ; well differentiated
squamous cell carcinoma)
• Micronodualr thymoma
• Metaplastic thymoma
• microscopic thymoma
• Scerosing lipoma
• Dual population of epithelial cells and lymphocytes in
• Cytological appearance depends on relative population of
• Epithelial V/S lymphoid cells
• Medullary V/S cortical component
Key diagnostic features of thymoma on FNAC
• 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
• Small no of extremely
elongated “ fibroblast like “
spindle cells may be seen.
• Hassall corpuscles are absent.
• Ck (+) , CD 20 (+) – epithelial
• Background lymphoid cells
• Thymic medullary cells CD
57 (+) neoplastic cells CD5(-)
• 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
• Soft tissue tumors ( solitary fibrous tumors and synovial
sarcoma ) – IHC
• Spindle cell carcinoid
• Benign mesothelial cell clusters
• 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
Thymoma with predominance of cortical
• 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
lymphoid cells are TdT, CD1a
and CD99 positive
Differential diagnosis :
• Reactive lymphoid hyperplasia : polymorphous population of
lymphoid cells along with tingible body macrophages, and
• Cytological distinction between thymus and thymoma are
• 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.
• 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.
• Abundant malignant cells
with varying degree of
tumor necrosis +/-
• Nuclear pleomorphism ,
prominent nucleoli, coarse
• IHC : CK , CD-5, CD-117,
positive and CD-57
• Squamous cell carcinoma – 90% in asia.
• Basaloid carcinoma
• Mucoepidermoid carcinoma
• Lymphoepithelioma like carcinoma
• Sarcomatoid carcinoma
• Clear cell carcinoma
• Papillary adenocarcinoma
• Well – differentiated neuroendocrine neoplasm ( typical and
• Poorly differentiated neuroendocrine carcinomas ( large cell
and small cell )
• Undifferentiated carcinoma
• Combined thymic epithelial tumors ; including neuroendocrine
• 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 :
• Often occur in anterior mediastinum : 2-4 % of thymic
• May be associated with Cushing's syndrome, 25 % associated
with MEN I.
• Further divided in to:
• Well differentiated neuroendocrine carcinoma( typical and
• Poorly differentiated neuroendocrine carcinoma ( large cell and
small cell type )
Thymic neuroendocrine tumors
• 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
• Smears : abundunt cellularity.
• Dispersed or in loosly
• Necrotic cellular debris,
lymphoid cells, and histioid
cells in “ tigroid “
• Large round ovoid nuclei,
eosinophilic nucleoli and
• Mitosis and apoptosis is
• IHC: CD-117, PLAP pos. CK –
focally / weakly pos.
• Thymic carcinoma : CK , CD-117 and CD-5 pos
• metastatic non-small cell carcinoma – CK pos and
• 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
• 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,
• 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
• Admixture of epithelial and
• 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
• Squamous flakes and
epithelium can be mistaken
• R/O mixed germ cell tumor
• Rare type of non seminomatous germ cell tumor in young
• Often associated with teratoma ( teratocarcinoma ),
Choriocarcinoma, or seminoma.
• Cytologically embryonal carcinoma is indistinguishable
from poorly differentiated carcinoma of non germ cell
• Mitotically active tumor with malignant cells arranged in
poorly cohesive 3 D clusters , with syncitial growth pattern.
• Nuclear overlapping, vesicular
chromatin with prominent
nucleoli, with small to
moderate amount of
cytoplasm and ill defined cell
• IHC : CK, CD- 30 pos,
EMA, vimentin, CD-117 and
• Differential diagnosis:
• Thymic carcinoma.
• Metastatic non-small cell
• Yolk sac tumor.
• 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
• 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
• Small clusters and sheets of
pleomorphic tumor cells
• +/- microglandular and
• 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.
• Embryonal carcinoma.
• Thymic carcinoma
• Metastatic non-small cell
• 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
• Syncytiotrophoblastic giant cells with eosinophilic cytoplasm ,
pleomorphic nuclei, prominent nucleoli,
• Cytotrophoblasts are medium sized cells with vaculated
• Primary mediastinal large B cell lymphoma
• Precursor T lymphoblastic lymphoma/leukemia
• Anaplastic large T cell lymphoma , mature T cell
• MAT lyphoma.
• Hodgkin’s lymphoma.
• Histiocytic and dendritic cell tumors
• Myeloid sarcoma and extra-medullary acute
• 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
Monomorphic population ; centroblast like cells with round nuceli and
several small basophilic nucleoli.
• 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 )
• Children and in young adults.
• Heterogenous population of atypical lymphoid cells and
• 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
Hallmark cell with embryo like nucleus Doughnut cell
Hand mirror Multinucleated Multilobated
• 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
• Cortical type of thymoma : B1 and B2 :a diagnostic
pitfall, demonstration of monoclonality proves
• Reactive lymphoid hyperplasia : TDT neg
• Low grade non-Hodgkin’s lymphoma
• Small cell carcinoma
• 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
• Commonest neurogenic tumor in mediastinum.
• Common in posterior mediastinum : develop from peripheral
nerve, sympathetic and parasympathetic ganglion , neural tube
• 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 ) &
• 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
• Bland looking with indiscriminant small nucleoli, some nuclear
• Vague rosette formation may be seen ( HW )
• Majority of mediastinal neoplasms.
• MC from lung and are small cell type followed by breast, thyroid
SCC AdenocarcinomaSmall cell carcinoma
• 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
• 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.
• Mediatinal germ cell tumors; non seminomatous can be
mistaken for poorly differentiated non small cell carcinoma
of lung – clinical and serological correlation required for
• 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
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
In adults : thymoma represents commonest primary thymic
tumor, followed by mediastinal lymphoma.
Approach to mediadiastinal tumors
Step 1 : clinical history
• 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
History and relevant information for diagnosis
lymphoma , extra
nodal marginal B
small tumor cells
rhabdo, small cell
germ cell tumors
Diffuse large B cell
lymphadenitis , chronic
nodular sclerosis HL, deep
Thymoma ( medullary),
spindle cell thymic
Metastatic MM, diffuse
large B cell lymphoma
with sclerosis, sarcomas,
spindle cell SCC.
• 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.
• WHO pathology and genetics – tumors of lung, pleura, thymus and
• 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.