Diagnostic Cytology
Table 27.10 Tumors of the Retroperitoneum
Mesodermally derived
Smooth muscle
Blood vessels
Nerve sheath
nervous system
Arising from tissue remnants and heterotopic tissue
Embryonal carcinoma
endodermal sinus
Renal blastoma
Wilms' tumor
adrenal tissue
Lymph nodes
Metastatic neoplasms
cells w ith hyp erchrom atic nuclei, o r lipocytes show ing greater
v a ria b ility in size com pared w ith n orm al. These w e ll-d iffe re n -
tiated liposarcom as are so cytolog ically b lan d th a t th ey were
p reviously called atypical lip o m a to u s tu m o rs by Evans,159 b u t
because o f the inexorab le fatal outcom e in the retro p e rito ne um ,
th ey are n o w designated as w e ll-d iffere ntia te d liposarcom as.
D ed ifferentiated liposarcom as are recognized b y the coexist-
ence o f a w e ll-d iffere ntia te d lip osarcom atous c om p onent w ith
a dedifferentiated cellular com p onent th a t resembles p le o m o r-
phic M F H (Fig. 2 7.6 2 C ).159
By histology, w e ll-d iffere ntia te d liposarcom a m ay have a
fib rosclerotic and spindle cell c om p onent together w ith focal
atypical p leo m o rp hic nuclei.
P leo m o rp hic liposarcom a resembles M F H cytolog ically b u t
can be diagnosed o n the basis o f the d e m o nstra tio n o f lipoblasts
in smears. Lipoblasts m ay resem ble signet rin g cells o r m ay be
large vacuolated cells w ith hyp erchrom atic scalloped n uclei.160
The d iffe re n tia l diagnosis o f liposarcom a, depending o n the
subtype, includes m yxo id fibrosarcom a, M F H o f m yxo id type
and high-grade M FH , extraskeletal m yxo id chondrosarcom a,
and chord om a.166
Leiom yosarcom a is second in frequency to liposarcom a and fre-
q u en tly arises fro m the uterus, g row ing retrop eritoneally. The
smears are characterized by single cells and clusters o f cells w ith
ab und ant e osin o p hilic cytoplasm and in d istin c t cell borders.
The nuclei are p re d o m in a n tly cigar-shaped and contain fin e ly
granular c hrom a tin and in d istin c t nucleoli. T he cytoplasm is
u su a lly abund ant and syncytial. Leiom yosarcom as also occur
in tra -a b d o m in a lly in the mesentery. The d iffe re n tia l diagnosis
includes neurogenic sarcoma, and the high-grade tu m o rs m ay
resem ble M FH . S m o o th m uscle actin is detected b y im m u n o h is -
tochem istry. U ltrastructure o f d ifferentiated leiom yosarcom as
shows th in m yo fila m e n ts w ith dense bodies.
Malignant Fibrous Histiocytoma
M a lig n a n t fib rous h istio c yto m a is the m ost c om m o n sarcoma
o f late life, occurring p re d o m in a n tly in the muscles o f the
extrem ities fo llo w e d b y the re tro p e rito n e u m . P leom orp hic,
m yxoid , g iant cell, inflam m ato ry, and a ng iom atoid subtypes
have been described.161 In fla m m a to ry M FH s occur m ost com -
m o n ly in th e retro p e rito ne um and are com posed o f sheets o f
h istioc ytic and in fla m m a to ry cells. The histiocytes appear to be
xan th om atou s because o f p ro m in e n t cytoplasm ic lip id . These
tu m o rs are m ost o fte n confused w ith lym phocytic-depleted
H od g kin's disease. H istolog ically, m ost M FH s are cellular, w ith
a m ixtu re o f s to rifo rm and p leo m o rp hic areas. FN A o f lo w -
grade m yxo id M F H is com posed o f a m ixtu re o f fibroblast-
and h istioc yte-like cells in a m yxo id background. High-grade
M F H shows m arked nuclear atypia occurring in a m ixtu re o f
fib rob last- and h istioc yte-like cells w ith m u ltin u clea te d g iant
cells. T his m ay be im p ossib le to d ifferentiate fro m p leom orp hic
liposarcom a (Fig. 27.6 3 ).
Round cell Sarcomas
In the retrop eritoneum , the d iffe re n tia l diagnosis o f a sm all rou nd
cell tu m o r includes em bryonal rhabdom yosarcom a, extraskeletal
Ewing's sarcoma, neuroblastom a, and sm all-cell und ifferentiated
cell carcinom a and lym p h o m a (see C hapter 29).
Embryonal Rhabdomyosarcomas
E m b ryonal rhabdom ysarcom as are tu m o rs o f c h ild h o o d and
adolescence and occur m ost fre q u e n tly in the head and neck
region, fo llo w e d b y the urog enital tract and the retrop erito-
n eu m .145 By FNA, the cells m ay be sm all and ro u n d o r m ore oval
and spindled in a m yxo id background (Fig. 27.6 4 ). R habdom yo-
blasts, w h ic h are cells show ing an eccentric nucleus and m ore
ab und ant e o sin o p h ilic cytoplasm , m ay be fo un d . These m ay
be tadpole- o r racquet-shaped. Im m unop eroxid ase stains fo r
desm in and m yo g lob in are u su a lly positive, the m ore sensitive
stain being desm in, w h ic h m ay dem onstrate p ositive staining
even in th e m ost p o o rly d ifferentiated tum ors. By ultrastructure,
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