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The histological appearance ranges from pure epithelial to the pure
mesenchymal forms. A combination of above patterns may be present.
It is important for the pathologist to be aware of these patterns to
make a histologic differentiation between DMM and other neoplasms.
Image Link1
;
Image Link2 ;
Image Link3;
Image Link4 .
The three broad
histological types:
i) Epithelial ; ii) Sarcomatous/Fibrous ; & iii)
Biphasic or mixed.
50% - Pleural
and 75% - Peritoneal mesothelioma.
30% are
biphasic. 15% - 20%- Pure sarcomatous subtype.
Recognition of histopathologic patterns
of diffuse malignant mesothelioma in differential diagnosis of pleural
biopsies.Arch
Pathol Lab Med.
2005 Nov;129(11):1415-20.
EPITHELIAL
MESOTHELIOMA:
Image Link
In diffuse
mesothelioma epithelial DMM are the most commonly diagnosed histologic
type.
1. Tubulopapillary Pattern:
Mixture of small
tubules and papillary structures with fibrovascular cores, often with
clefts and trabeculae.
In Well
differentiated tumours the fibrohyaline papillae are lined by
neoplastic mesothelial cells -(uniformly cuboidal cells with large
vesicular nuclei and prominent nucleoli ). Psammoma bodies may
be present.
Image Link
D/D:
Adenocarcinoma metastatic to the pleura.
2. Acinar Pattern:
Characterized by
acinar or glandlike structures.
D/D: Metastatic
adenocarcinoma.
3. Adenomatoid
Pattern (also
termed microglandular):
Small
gland-like structures lined by bland flat to cuboidal cells.
D/D:
Metastatic
adenocarcinoma.
4. Small cell
pattern : Sheets of monotonous small hyperchromatic uniform cells
with a high nucleocytoplasmic ratio.
D/D: This variant may mimic small cell
carcinoma or lymphoma. Nuclear karyorrhexis and haematoxyphilic
vessels are not a feature in mesothelioma . Lymphoma is distinguished
from small cell variant of mesothelioma by immunohistochemical
examination.
5. Deciduoid
Pattern:
Identified in the pleura of elderly patients.
Histologically the tumour is characterized by proliferation of large,
round to polygonal cells with sharp cell borders, abundant glassy
eosinophilic cytoplasm, and round vesicular nuclei with prominent
nucleoli.
D/D:
Squamous
cell carcinoma, trophoblastic neoplasia , gastrointestinal
autonomic nerve tumour , anaplastic large cell lymphoma, oxyphilic
variant of ovarian clear cell carcinoma .
6. Signet
Ring (Lipid-Rich) Pattern: Tumour cells exhibiting secretory
change with cytoplasmic vacuolation.
D/D:
Metastatic Signet ring cell adenocarcinoma.
7. Clear
Cell Pattern: There are tumor
cells with clear cytoplasm. Other patterns may be present in the
tumour.
D/D:
Clear cell tumours that are
metastatic to the pleura - Eg. Renal cell carcinoma, clear cell
carcinomas of the lung, clear cell melanoma.
8. Adenoid
Cystic:
Cribriform
and tubular growth patterns set in a fibrous stroma.
D/D:
Metastatic adenoid cystic carcinoma and adenocarcinoma.
9.
Solid Pattern: Well differentiated &
Poorly
differentiated-
Well
differentiated-
Nests and sheets
of round cells with abundant cytoplasm and round, vesicular nuclei
with prominent nucleoli. Mitoses are usually not prominent.
D/D: Benign
reactive mesothelial hyperplasia
Poorly
differentiated- Monotonous sheets of cytologically malignant
polygonal cells with abundant glassy eosinophilic cytoplasm with
uniform nuclei.
D/D: Lymphoma
and large cell carcinoma.
SARCOMATOUS
MESOTHELIOMA:
Image Link1 ; Image
Link2
Sarcomatoid
mesothelioma is composed of a fascicular proliferation of spindle
cells with oval nuclei, scanty cytoplasm and occasionally prominent
nucleoli.
Image Link 3
Tumour cells
display a
fibrosarcoma-like appearance with
elongated fascicles showing herringbone formations and abundant
intercellular collagen deposition.
Tumour may
show a prominent storiform appearance indistinguishable from that of
malignant fibrous histiocytoma.
Sarcomatoid
mesothelioma show i) more atypia ii) display mitotic activity
iii) foci of necrosis.
Lymphohistiocytoid mesothelioma: Histologically, the tumour
is characterized by a diffuse discohesive proliferation of
atypical histiocytoid cells intermixed with a marked lymphocytic and
moderate plasmacytic infiltrate.
In
lymphohistiocytoid mesothelioma, the demonstration of cytokeratin
expression by the neoplastic cells is the most useful diagnostic
finding that allows exclusion of other neoplasms with which this
entity may be confused.
Desmoplastic
mesothelioma: This is a rare variant of malignant mesothelioma with a
storiform collagen pattern, collagen necrosis, bland acellular
collagen and focal cytological features of malignancy. Though rare, it
is important to recognise this variant and distinguish it from a
pleural plaque, nonspecific reactive pleural fibrosis, pleurisy,
rheumatoid disease, or, rarely, spindle cell sarcomas.
BIPHASIC (MIXED)
MESOTHELIOMA:
ImageLink1
;
ImageLink2
Characterized by
a combination of epithelial and sarcomatoid patterns. D/D:
Carcinosarcomas, biphasic pulmonary blastoma, and
biphasic synovial sarcoma.
MISCELLANEOUS PATTERN:
Pleomorphic :
Both
epithelial and sarcomatous pattern are present ; There are tumour
giant cells and anaplastic cells .
Transitional :
Tumor
cells with a “transitional” appearance, displaying both epithelial and
sarcomatous features in the same cell. |
