2017, Volume 33, Number 1, Page(s) 037-046
Clinicopathological Analysis of Mediastinal Masses: A Mixed Bag of Non-Neoplastic and Neoplastic Etiologies
Preeti SHARMA1, Vidya JHA1, Naveen KUMAR2, Rohit KUMAR3, Ashish MANDAL1
1Department of Pathology, Vardhman Mahavir Medical College & Safdarjung Hospital, New DELHI, INDIA
2Department of Radiodiagnosis, All India Institute of Medical Sciences, NEW DELHI, INDIA
3Department of Cardiology, Medanta Medcity, GURGAON, INDIA
Keywords: Mediastinum, Thymoma, Lymphoma, Seminoma, Neurogenic tumours
The mediastinum is the central portion of the thoracic cavity, housing numerous organs and harbouring a mixed bag of non-neoplastic
and neoplastic lesions. Accurate diagnosis is essential owing to the widely variable therapeutic and prognostic implications.
Material and Method: Cases of mediastinal masses were retrospectively reviewed from January 2011 till January 2016. Clinico-radiological
records of these cases were retrieved. Fine needle aspiration cytology (FNAC) was performed wherever feasible. Histopathological and
immunohistochemical evaluation of the excised specimens was undertaken.
Results: Of the 60 cases included in our study, 22 were anterior, 20 were middle and 18 posterior mediastinal masses. The majority of the
patients were symptomatic (96.8%). The most common pathology was thymoma (12 cases) followed by ten cases of lymphoma, eight cases each
of tubercular lymphadenopathy and schwannoma, six cases of neurofibroma, four cases of extragonadal germ cell tumours, two cases each of
thymic cyst, bronchogenic cyst, retrosternal goitre, ganglioneuroma and neuroblastoma, and one case each of lipoma and thymolipoma. FNAC
was done in 54 cases of which 7 cases yielded inadequate material. Immunohistochemistry was required for classification of lymphoma cases and
confirmation of a mixed component in germ cell tumours.
Conclusion: Mediastinal masses create significant diagnostic dilemma for the clinicians, radiologists and histopathologists. While imaging
studies help in narrowing the differential diagnosis, accurate categorisation is not always possible. FNAC is a useful and cost effective tool.
However, sampling error and complexities in performing the technique are major hurdles in the usefulness of this diagnostic modality.
The mediastinum extends antero-posteriorly from the
sternum to the spine and from the thoracic inlet down to the
diaphragm. The so-called Pandora’s Box has been divided
into four compartments, i.e. superior, anterior, middle and
posterior. While imaging studies suggest the location of
the lesion and help in narrowing the differential diagnosis,
morphological assessment by fine needle aspiration cytology
(FNAC) or histopathological examination is imperative
prior to therapeutic intervention. Although FNAC is a
cost effective tool for the establishment of pre-operative
diagnosis of mediastinal masses, there is a complexity and
technical difficulty associated with this technique owing to
the narrow anatomic space of mediastinum. Also, there are
well known diagnostic pitfalls of this technique that limit
Despite being a well-delineated narrow space, the diversity
of lesions arising in the mediastinum pose an interesting
diagnostic challenge for the clinicians, radiologists and pathologists2. There is limited data regarding the clinical
and pathological features of these enigmatic mediastinal
Our study highlights the clinico-pathological features
in patients presenting with mediastinal masses with
special emphasis on the utility of pre-operative diagnostic
modalities like imaging and FNAC.
The archives of the Department of Histopathology were
retrospectively reviewed over a period of five years
from January 2011 to January 2016. Of the 65,089 cases
received in our department, patients who underwent
surgical excision for mediastinal masses were included
in this study. Patients with bronchogenic, esophageal
and metastatic tumours were excluded. Clinical details
including detailed history, physical examination and
results of routine blood investigations were obtained. Preoperative
chest radiographs were obtained in all patients with suspected mediastinal lesions, following which
computed tomography (CT) was performed for further
characterisation of the lesion. CT-guided fine needle
aspiration (FNAC) was performed wherever possible.
Aspirates were smeared on clean glass slides, air dried and
stained by May-Grünwald-Giemsa (MGG) stain. There
were no cell block preparations studied. Following surgical
excision, the excised specimen was fixed in 10% neutral
buffered formalin and sent for histopathological evaluation.
Diagnosis was confirmed on hematoxylin and eosin
(H&E)-stained formalin-fixed paraffin-embedded sections.
For cases in which final diagnosis could not be made on
routine examination, a detailed immunohistochemical
panel comprising of cytokeratin (CK), cluster of
differentiation 45 (CD 45), CD 20, CD3, CD15, CD 30 and
TdT was applied. Further, OCT-3/4, alpha feto protein
(AFP) and beta-human chorionic gonadotropin (β-HCG)
were applied to rule out a mixed component, if any, in a
germ cell tumour. In brief, sections measuring 3-4 μm thick
were cut, deparaffinized with xylene and brought to water
through graded levels of alcohol. Endogenous peroxidase
activity was blocked by treating the slides with hydrogen
peroxide for 30 min at room temperature. Antigen retrieval
was done by immersing the slides in citrate buffer using the
pressure cooker method. The slides were then incubated
overnight with the primary antibody (rabbit polyclonal)
at 4 ˚C in a humidified chamber. The following day,
secondary antibody was added. The sections were then
incubated with di amino benzidine (DAB) for visualization
of the peroxidase reaction. After being washed in water, the sections were counter stained with haematoxylin,
dehydrated in alcohol, cleared in xylene and mounted.
Immunohistochemistry (IHC) was interpreted in a binary
fashion as positive or negative.
The FNAC smears, H&E stained sections and
immunohistochemistry slides were reviewed by two
pathologists and correlated with the clinical findings
Of the 65,089 cases received in our department, 60 patients
with mediastinal masses were included in the study.
Among these, the majority of the patients presented with a
mass in the anterior mediastinum (36.7%), followed by the
middle mediastinum (33.3%) and posterior mediastinum
(30%). The compartment-wise histopathological diagnosis
of the mediastinal masses is described in Table I
. The mean
patient age at the time of presentation was 37.5 years (range
2-61 years). There were 43 males and 21 females with a
male: female ratio of 2:1.
Retrospective analysis of the clinical and radiological
findings of these patients was done. The most common
presenting complaint was cough, seen in 54 patients
(87.0%), followed by chest pain (50; 80.6%), weight loss (36;
58.0%), dyspnoea (26; 41.9%) and hoarseness (14; 22.5%).
Myasthenic symptoms were seen in four patients with
thymoma (Table II). Two patients each of thymic cyst and
mediastinal lipoma were diagnosed incidentally. Routine
blood investigations including complete hemogram, liver function tests and kidney function tests were normal in
all patients except four cases of tubercular lymphadenitis
with raised erythrocyte sedimentation rate (ESR). Chest
X-ray showed mediastinal widening in 40 patients. CT
scan revealed the presence of mediastinal masses in
their respective compartments in all cases. Mediastinal
lymphadenopathy was noted in 18 cases on CT scan. CT
guided FNAC was performed in 54 patients.
Histopathological examination revealed 73.33% benign
and 26.67% malignant lesions. Among the twelve cases of
thymoma, the most common variant was the AB subtype (9
cases) followed by two cases of B1 subtype and one case of
thymic carcinoma. Thymic tumours were classified as per
the World Health Organisation (WHO) classification. Six
patients with anterior mediastinal masses showed a biphasic
population of spindle-shaped epithelial cells interspersed
with lymphoid cells on FNA smears. A provisional diagnosis
of thymic hyperplasia versus thymoma was considered.
The excision biopsy specimen showed features suggestive
of thymoma, AB subtype. On the other hand, FNA smears
from three patients predominantly showed presence of
haemorrhage along with few scattered lymphoid cells and
were inconclusive. Subsequently they were diagnosed as thymoma, AB subtype on histopathological examination
(Figure 1A-C). Two female patients suffering with
myasthenia gravis, aged 42 years and 46 years respectively,
showed cellular FNA smears consisting of monomorphic
lymphoid cells. A few scattered spindle-shaped epithelial
cells were also seen along with occasional atypical mitosis.
Differential diagnosis of lymphoma versus thymoma was
considered. Histopathology revealed diffuse effacement
of thymic architecture by a monomorphic population
of lymphoid cells intermixed with epithelial cells. On
IHC, the lymphoid cells were positive for TdT and CD3
while the epithelial cells were positive for CK, thereby
excluding lymphoma. A final diagnosis of thymoma, B1
subtype was made in both the cases. On the other hand,
an elderly female presented with a rapidly enlarging
mediastinal mass associated with vague chest pain and
dyspnoea. Histopathological examination revealed an unencapsulated,
poorly circumscribed tumour composed
of large polygonal cells arranged in nests and diffuse
sheets. The individual tumour cells were polygonal with
moderate amount of dense eosinophilic cytoplasm and
central vesicular nucleus with single nucleolus. Numerous
atypical mitoses and tumour necrosis were seen. Foci of
keratinisation were evident. Features were suggestive of
keratinizing squamous cell carcinoma in concordance with
the FNAC findings. A thorough clinico-radiological work
up was done to rule out the possibility of metastasis, and a
final diagnosis of primary thymic carcinoma was rendered.
Mediastinal lymphadenopathy was seen in 18 cases. Among
10 cases of lymphoma, there were 6 cases of Non- Hodgkin
Lymphoma (NHL) and four cases of classical Hodgkin
lymphoma (HL). There was no difficulty in FNAC diagnosis
of these lesions except for three cases predominantly
showing haemorrhage with few scattered lymphoid cells, inconclusive for an opinion. Histologically, most common
type of NHL was diffuse large B cell lymphoma, seen in
5 cases (Figure 2A-D). On IHC the cells were positive
for CD45, CD19, CD20 and negative for CD15, CD30
and EMA. Nodular sclerosis subtype was reported in all
4 cases of Hodgkin’s lymphoma. IHC showed that the
Reed-Sternberg (RS) cells were positive for CD45, CD
15 and CD 30 (Figure 3A-F). In another case, a 45-yearold
man presented with dyspnoea and excision biopsy of
the mediastinal lymph node revealed diffuse effacement
of architecture by clusters of epithelioid histiocytes.
Interspersed in between were small lymphoid cells with scant cytoplasm and round to oval hyperchromatic nuclei
showing mild atypia. Few binucleate RS like cells were also
seen. On IHC, the lymphoid cells were positive for CD45
and CD3. The RS like cells were negative for CD15 and
CD30, thereby excluding Hodgkin’s lymphoma (Figure
4A-F). Thus a final immunomorphological diagnosis of
Lennert’s lymphoma was rendered. On the other hand,
necrotizing granulomatous lymphadenitis was seen on
histopathology of the remaining 8 patients with mediastinal
lymphadenopathy. Stain for acid fast bacilli (AFB) was
positive in these cases and a diagnosis of tubercular
lymphadenitis was given (Figure 5A,B). Of these, seven patients had disseminated tuberculosis while one patient
was diagnosed with isolated tubercular lymphadenopathy
involving the mediastinal lymph nodes only.
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|Figure 1: A) CT scan of a case of thymoma showing symmetrical diffuse enlargement of thymus. B) FNA smear showing biphasic
population of spindle-shaped epithelial cells (arrow) interspersed with lymphoid cells (arrow head) (May Grünwald Giemsa; x200).
C) Presence of lymphocytes (arrow head) admixed with thymocytes (arrow) favouring thymoma- AB sybtype (H&E; x200).
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|Figure 2: A) CT scan shows a large anterior mediastinal mass measuring 16x11 cm with central necrotic area invading into the adjacent
myocardium and involving the pulmonary artery, ascending aorta & left lung upper lobe, suggestive of lymphoma. B-C) Diffuse arrangement
of monomorphic population of immature lymphoid cells in FNA smears (May Grünwald Giemsa; x200). D) Diffuse effacement of lymph
node architecture by large atypical lymphoid cells suggestive of NHL (H&E; x200).
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|Figure 3: A) CT scan shows a homogeneous soft tissue mass in superior and anterior mediastinum encasing the great vessels without
narrowing them. B) FNA smear showing classical RS cells seen in a case of HL (May Grünwald Giemsa; x200). C) Polymorphous
background comprising of lymphocytes, eosinophils and macrophages (H&E; x200). D) Classical RS cell against a polymorphous
background (H&E; x200). E) RS cells are positive for CD15 (CD15; x200). F) RS cells are positive for CD30 (CD30; x200).
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|Figure 4: A) CT scan of a case of Lennert’s lymphoma showing enlarged paratracheal and subcarinal nodes showing homogeneous
enhancement. B) Diffuse effacement of lymph node architecture by clusters of epithelioid histiocytes (arrow) interspersed with lymphoid
cells (H&E; x100). C) Higher magnification shows lymphoid cells with scant cytoplasm and round to oval hyperchromatic nuclei showing
mild atypia. Few binucleate RS like cells are also seen (inset) (H&E ; x200). D) Lymphoid cells are positive for CD3 (CD3; x200). E) RS
like cells are negative for CD 15 (CD15; x200) and F) CD30 (CD30; x200).
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|Figure 5: A) Epithelioid cell granulomas in a lymph node (H&E; x200). B) Stain for acid fast bacilli is positive (inset) diagnostic of
tubercular lymphadenitis (Ziehl-Neelsen; x200)
Germ cell tumours were seen in four cases located in the
anterior mediastinum. Two cases showed moderately
cellular FNA smears against a tigroid background with
presence of scattered lymphocytes. The individual tumour
cells were large with moderate amount of vacuolated
cytoplasm and a large vesicular nucleus with one or
two prominent nucleoli. Provisional diagnosis of germ
cell tumour, possibly seminoma, versus lymphoma
was considered. Histopathological examination and
immunohistochemical positivity for OCT3/4 confirmed the
diagnosis of classical seminoma in both these cases (Figure
6A-C). A single case of mature teratoma (Figure 6D-F) was
diagnosed in a 22-year-old male patient. CT scan revealed a
large mediastinal mass involving the anterior mediastinum
with foci of calcification. FNA smears showed presence of
nucleated and anucleated squamous cells only. Another
case was diagnosed as mixed germ cell tumour showing
histomorphological features of seminoma and yolk sac
tumour confirmed by OCT3/4 and AFP IHC respectively. While there was no difficulty in the FNA diagnosis of
seminoma, the yolk sac component could not be identified
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|Figure 6: A) CT scan of a case of seminoma showing an anterior mediastinal mass with internal calcifications along with multiple
nodular metastases seen in both lungs. B) FNA smear showing large atypical cells against a blood mixed tigroid background. The cells
show vacuolated cytoplasm (arrow) and a vesicular nucleus with prominent 1-2 nucleoli (inset) (May Grünwald Giemsa; x200) C) Large
tumour cells separated by thin fibrous septae infiltrated by lymphocytes. The tumour cells have clear cytoplasm and a central vesicular
nucleus with prominent nucleoli favouring mediastinal seminoma (H&E; x200). D) CT scan of a case of teratoma showing soft tissue
mass in anterior mediastinum with internal calcific foci. E) FNA smear shows anucleated squamous cells (May Grünwald Giemsa;
x400). F) Keratinized stratified squamous epithelium with skin appendages, fat, cartilage and glands lined by tall columnar epithelium
suggestive of mediastinal teratoma (H&E; x200).
Eighteen cases of neurogenic tumours were identified in
the posterior mediastinum. Of these, schwannoma was the
most common and seen in 8 patients (Figure 7A), followed
by six cases of neurofibroma (Figure 7B) and two cases of
ganglioneuroma. FNA smears in the majority of these cases
were moderately cellular with presence of spindle-shaped
cells either in clusters or singly scattered. The individual
cells were spindle-shaped with scant to moderate cytoplasm
and hyperchromatic spindle-shaped nucleus. No Verocay
bodies, nuclear atypia or stromal fragments were seen. A
provisional FNA diagnosis of spindle cell tumour was given
in ten of these cases, while the remaining cases showed
paucicellular smears and were labelled inconclusive for
opinion. Two cases of neuroblastoma (Figure 8A,B) were
seen in a 2- and 4-year-old male child respectively, FNA
smears of which were inadequate for diagnosis.
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|Figure 7: A) Numerous Verocay bodies in a case of schwannoma (H&E; x200). B) Neurofibroma showing spindle-shaped cells arranged
in bundles with cells showing moderate eosinophilic cytoplasm with hyperchromatic wavy spindle-shaped nuclei (H&E; x200).
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|Figure 8: A) CT scan showing large heterogeneous mass with internal calcifications in the right hemithorax replacing the right lung. B)
Diffuse sheets of small round blue cells with formation of rosettes (inset) suggestive of neuroblastoma (H&E; x200).
Cystic lesions of the mediastinum consisted of two cases
each of bronchogenic cyst, thymic cyst and retrosternal
goitre with cystic change respectively, diagnosed on histopathological examination of the excised specimen.
FNAC was not performed in these cases owing to the cystic
nature of the lesion. One case each of mediastinal lipoma
was readily diagnosed on cytology and confirmed on
histopathology. Also, a 22-year-old female patient showed
a large fat-containing anterior mediastinal mass extending
along the right pericardium on CT scan (Figure 9A). FNA
showed features suggestive of lipoma. On histopathology,
a well-encapsulated tumour was seen showing intermixed
thymic tissue within mature adipocytes, suggestive of
thymolipoma (Figure 9B).
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|Figure 9: A) CT scan showing a large fat containing anterior mediastinal mass extending along the right pericardium. B) Thymic tissue
intermixed with mature adipocytes suggestive of thymolipoma (H&E; x200).
Primary mediastinal tumours are rare, accounting for 3%
of tumours occurring within the chest3
. We studied
60 cases of mediastinal lesions received over a period of
5 years. The mean patient age was 37.5 years (range 2-61
years) with a male preponderance. Our findings were in
concordance with the previously published literature2,4
Nearly 50% of all mediastinal masses involve the anterior
compartment, including thymoma, teratoma, lymphoma,
thyroid and parathyroid lesions. Congenital cysts and neurogenic tumours are most commonly observed in the
middle and posterior mediastinum respectively3. In our
study, the anterior compartment (36.7%) was maximally
involved followed by the middle mediastinum (33.3%) and
posterior mediastinum (30%). Thymoma was the most
common tumour of the anterior compartment followed
by germ cell tumours. The middle mediastinum showed
mainly nodal involvement with lymphoma most commonly
followed by tubercular lymphadenitis. Neurogenic tumours
were seen in the posterior mediastinum only. Studies
conducted in the past showed nearly similar trends5-7.
In the present study, 96.8% of the subjects were
symptomatic at presentation. Dubashi et al.5 reported
a similar incidence of 97% with other studies reporting a
range of 60-88%2,4.
In 1987 however, Davis et al.4 reported a much higher
incidence of asymptomatic cases (38%). This difference
may be attributed to the fact that most of the patients in
our setting visit the hospital for their symptoms rather than
for routine examination. The most common symptoms
reported in this study was cough followed by chest
pain, dyspnoea and weight loss which was similar to the
previously reported incidence8,9.
Pre-operative diagnosis of mediastinal masses is a
challenging task owing to the non-specific clinicoradiological
signs and technical difficulty in performing
FNAC. The investigation of choice for the detection of
mediastinal masses is CT scan10. Magnetic resonance
imaging (MRI) is of help in further categorisation of the
lesions11. In our study, CT scan identified mediastinal
masses in all cases but was unable to categorise the lesion
in any. CT scan thus helps in compartment localisation of
the mediastinal mass. This further helps in narrowing the
probable differential diagnosis.
CT‑guided FNAC is a safe, useful and cost-effective
method for the diagnosis of mediastinal masses. However,
close proximity to vital organs can be a hindrance for this
technique. In our study, FNAC was performed in 54 cases.
There were 7 cases which revealed inadequate material.
Thymic lesions often pose a diagnostic challenge for the
reporting cytologist. While the lymphocyte-rich variant
of thymoma (B1 subtype) can easily be misdiagnosed as
lymphoma11, epithelial rich variant (A subtype) on the
other hand is a close mimicker for carcinoma12. Similar
to previous studies, our study also highlights the difficulty
encountered in the FNA diagnosis of thymic lesions
especially two cases of B1 subtype where the possibility of
a lymphoma could not be ruled out and six cases of AB subtype in which thymic hyperplasia versus thymoma
could not be accurately diagnosed on FNAC. Thymic
carcinoma on the other hand was readily diagnosed due to
the frank malignant features.
Apart from the thymic lesions, neurogenic tumours
are difficult to categorise on cytology. Schwannomas
are usually difficult to differentiate from neurofibroma
unless characteristic Verocay bodies are seen, while
ganglioneuroma cannot be diagnosed till ganglion cells are
aspirated. Both these findings were not seen in our cases
and a final diagnosis of spindle cell tumour was rendered on
FNAC. Further, some degree of cellular and nuclear atypia
is commonly seen in neurogenic tumours. This warrants a
careful search for mitotic figures and excision biopsy for
proper histopathological evaluation. Thus characterisation
of benign versus malignant on FNAC is a diagnostic
difficulty which is then overcome on histopathology. On the
other hand, germ cell tumours cannot readily be diagnosed
on FNAC since tigroid background is not entirely specific
for seminoma and when lymphocytes/ lymphoglandular
bodies are present, a confusion with malignant lymphoma
is possible, as seen in two of our cases. Furthermore,
smears showing discohesive pattern on cytology should be
differentiated from poorly differentiated adenocarcinoma,
melanoma and lymphoma. In our study, the component of
yolk sac tumour was missed in a single case of mixed germ
cell tumour. This can be attributed to selective sampling
which is a well-known hurdle in aspiration cytology.
As reported earlier by Chhieng et al. particularly in case
of mixed germ cell tumours may also pose diagnostic
challenge13. Similarly, fat fragments were selectively
sampled from an anterior mediastinal mass in a 22-yearold
female which was diagnosed later as thymolipoma on
A rather rare case encountered in our study which deserves
special mention was Lennert’s lymphoma in a 33-year-old
male patient with mediastinal lymphadenopathy involving
the middle compartment. Lennert’s lymphoma is a variant
of peripheral T-Cell lymphoma, not otherwise specified in
the WHO classification of 200814. Its rarity and the lack
of strict diagnostic criteria explain why only a few reports
on Lennert’s lymphoma have been published so far. Our
case showed presence of RS like cells mimicking Hodgkin’s
lymphoma and posed the same diagnostic dilemma as the
previously published cases. In 2013, Parimal et al.15
reported a series of 5 cases of Lennert’s lymphoma which
constituted 0.71% of all peripheral T-cell lymphomas in
their institution. They concluded that classical Hodgkin’s
lymphoma is a close mimicker of Lennert’s lymphoma and suggested T cell gene rearrangement studies when
distinction cannot be made on morphology and IHC.
To conclude, we evaluated the role of clinico-radiological,
cytological and histopathological findings in the differential
diagnosis of mediastinal masses. Owing to rather nonspecific
clinical and radiological signs, histopathological
examination remains the mainstay of diagnosis. Further,
the proximity of this area to vital visceral organs decreases
the usefulness of FNAC and leads to a failure to adequately
describe cytomorphological characteristics of the mediastinal
CONFLICT OF INTEREST
The authors declared no conflict of interest.
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