29
Pediatric Tumors
com m a-shaped nuclei arranged in the m id d le o f lax strom a
fragm ents and m yxoid. Cells are im m un ore ac tive fo r v im e n tin ,
S-100 p rotein, and Leu7.37
Key features of neurofibroma
• Few sp in d le cells;
• E lon g ated com m a -sh a p ed n u c le i; and
• Frag m ents o f m y x o id strom a .
M alignant N eurogenic Tumors
T he m ost freq uent m a lig n a n t neurogenic tu m o r is P N E T-E W S .
M a lig n a n t peripheral nerve sheath tu m o r is rare. P N E T -E W S is
one o f the m ost freq uent soft tissue sarcomas in children, and
ab out 15% o f them produce a soft tissue tu m o r w ith o u t bone
in vo lve m e n t.35,36 FN A o f these lesions is described w ith bone
tu m o rs.37
Fibroblastic and Myofibroblastic Tumors
Fibroblastic and m yofib rob lastic tu m o rs fo rm an im p o rta n t
group o f soft tissue tu m o rs in children. Som e o f them are benign,
such
as
fib rom atosis
(in fa n tile
m yofib rom atosis,
desm oid
fib rom atosis, and fib rom atosis c o lli), and som e are m alig nant,
such as fibrosarcom a (Fig. 29.10C ).35,36 Fine-needle aspirates
in fib rom atosis are o fte n slig htly cellular and show n o rm o -
typic spindle cells, w h ic h are isolated o r in three-d im ensional
fragm ents w ith collagenous strom a (Fig. 29.10D ). Fine-needle
aspirates o f fibrosarcom as show atypical spindle cells w ith large
hyp erchrom atic nuclei, num erous m itoses, and a necrotic back-
g round .37
Key features of fibromatosis
• S lig h tly c e llu la r aspirates;
• N o rm o ty p ic sp in d le cells; and
• C le a n b ackg round .
Myogenic Tumors
Skeletal m uscle tu m o rs in child ren are m uch m ore freq uent
th an those o f sm o oth muscle. They account fo r about 13% o f
soft tissue tum ors, and the m a jo rity are m a lig n a n t (9 8 % ).35,36
Rhabdomyom a
R hab d om yom a is an infre q u e n t benign m uscle tu m o r, often the
fetal type, and is m ore freq uent in child ren young er th a n 3 years;
it is fo u n d in the head and neck, derm is, o r subcutaneous tissue.
Fine-needle aspirates show im m a tu re m uscle fibers w ith m u l-
tip le nuclei and transverse s tria tio n and arranged in lob ulated
bundles. The presence o f cellu la r atypias and h yp e rce llu la rity
suggests a rhabdom yosarcom a.35,36
Rhabdomyosarcom a
Sarcom a w ith a striated m uscle phenotype is often associated
w ith developm ental and hered itary diseases such as L i-F ra u m e n i
syndrom e, retinob lastom a, and von Recklinghausen's n e u ro fi-
brom atosis. It is the m ost freq uent soft tissue sarcom a in children
(~ 50% ); it arises often in the head and neck (38% ), u rin a ry tract
(26% ), extrem ities, and tru n k (17 % ) o f patients less th a n 5 years
old. The in te rn a tio n a l classification o f rhabdom yosarcom as
subdivides these tu m o rs in to five types w ith d iffe re n t b iolog ic
behaviors: em bryonary, n o t otherw ise specified; em b ryonary
b o tryo id ; fusocellular; alveolar; and und ifferentiated .
E m b ryonary rhabdom yosarcom a accounts fo r m ore than
h a lf o f cases; its frequency varies am ong age groups, and it is the
m ost freq uent subtype in child ren less th an 10 years. It is form ed
b y blastem ic cells fro m u n d iffe ren tia te d to w e ll-d iffere ntia te d
m uscular ones. C e llu la rity varies fro m one tu m o r to the next
and fro m one region o f the tu m o r to the next. S trom a is often
m yxoid , and there is condensation o f tu m o ra l cells in a few
cellular zones. Fine-needle aspirates o f em b ryonary rhab d o-
m yosarcom as show m an y oval o r spindle rhab d om yob lastic cells,
som e o f w h ic h present cross-striations, and less-differentiated
stellate cells w ith scanty cytoplasm and few und iffe ren tia te d
spindle cells (Fig. 29.10E).
B otryo id rhabdom yosarcom a requires the presence o f cam -
b iu m layer (the overlying e p ith e liu m m ust be intact and subepi-
th e lia l condensation o f tu m o r cells present).
Fusoc e llular rhab d om yosarcom a shows scarce cells a lm o s t
exclusively sp ind led and arranged in a s to rifo rm p attern
(Fig. 2 9.1 0 F). A lv e o la r rhab d om yosarcom a is th e m o st fre -
q u e n t in adolescents and shows fib ro u s septa anastom osed
and covered by neop lastic ro u n d cells w ith scarce e o s in o p h ilic
cytoplasm and occasionally g ia n t m u ltin u c le a te d cells.35,36
Fine-need le aspirates sho w iso la te d ro u n d cells th a t are sm a ll
o r m id sized (w ith o u t rosettes), w ith scarce o r a b un d an t cyto-
plasm and elongated and ro u n d n uclei w ith th in c h ro m a tin
and g ra n u la r and som etim es p ro m in e n t n u c le o li.37,38 Elec-
tro n m icroscopy can reveal skeletal m uscle d iffe re n tia tio n in
rhabdom yosarcom as.
R hab d om yosarcom a is
im m un ore ac -
tive fo r v im e n tin , m yogenic m yo D 1, m uscle-specific actin,
d esm in, and m yo g lo b in .
Cytogenetics and m olecular genetics have diagnostic and
prognostic im portance. Tw o m a in translocations have been
id en tifie d in the alveolar rhabdom yosarcom a— 1(2;13)
and
t(1 ;1 3 )— w h ic h can be detected b y cytogenetics, conventional
reverse transcriptase polym erase chain reaction, and fluorescence
in situ h yb rid iza tio n (FISH ). D iffe re n tia l diagnosis w ith other
ro u n d cell m alig n an t tum ors, such as lym p h om a, leukem ia,
neuroblastom a, P N E T-E W S , sin ovial sarcoma, soft tissue alveo-
la r sarcoma, and m alig n an t rhab d oid tu m o r, m ust be made, fo r
w h ic h im m un oc yto ch em istry is essential.35,36
Key features of embryonary rhabdomyosarcoma
• M a n y s m a ll cohesive cells;
• O v a l o r sp in d le rh a b d o m y o b la stic cells; and
• S om e cells w ith cross-striations.
Fibrohistiocytic Tumors
F ib ro histio cytic tu m o rs fo rm an im p o rta n t and heterogeneous
group o f soft tissue tu m o rs th a t are capable o f d iffe re n tia tio n
in to fibroblastic, histiocytic, and m yofib rob lastic tu m o rs.35,36
Benign Fibrohistiocytic Tum ors
Benign Fibrous Histiocytoma
Benign fib rous h istio c yto m a is the m ost freq uent fib roh istioc ytic
tu m o r in child ren and shows im p o rta n t c lin ic a l-p a th o lo g ic d if-
ferences depending o n depth o r superficiality.
Benign fib rous histiocytom as are congenital in 18% o f
cases and m ore freq uent in child ren young er th a n 10 years.
They locate m ostly in the head, neck, and tru n k, except fo r
d erm atofib rom as (derm al fo rm ), w h ic h locate p refere ntially in
the extrem ities.35,36
939
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